select post-quantum KEX sntrup761x25519-sha512@openssh.com as the
default; ok markus@

add the sntrup761x25519-sha512@openssh.com hybrid ECDH/x25519 +
Streamlined NTRU Prime post-quantum KEX to the default KEXAlgorithms
list (after the ECDH methods but before the prime-group DH ones).

ok markus@

After years of forewarning, disable the RSA/SHA-1 signature algorithm
by default. It is feasible to create colliding SHA1 hashes, so we
need to deprecate its use.

RSA/SHA-256/512 remains available and will be transparently selected
instead of RSA/SHA1 for most SSH servers released in the last five+
years. There is no need to regenerate RSA keys.

The use of RSA/SHA1 can be re-enabled by adding "ssh-rsa" to the
PubkeyAcceptedAlgorithms directives on the client and server.

ok dtucker deraadt

prefer ed25519 signature algorithm variants to ECDSA; ok markus@

remove ssh-rsa (SHA1) from the list of allowed CA signature algorithms
ok markus

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY

branches: 1.18.2; 1.18.4;
add a new compression method that delays compression until the user
has been authenticated successfully and set compression to 'delayed'
for sshd.

this breaks older openssh clients (< 3.5) if they insist on
compression, so you have to re-enable compression in sshd_config.
ok djm@

add support for draft-harris-ssh-arcfour-fixes-02 improved arcfour modes;
ok markus@

branches: 1.16.2; 1.16.4;
implement diffie-hellman-group14-sha1 kex method (trivial extension to
existing diffie-hellman-group1-sha1); ok markus@

branches: 1.15.2; 1.15.4;
experimental support for aes-ctr modes from
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-00.txt
ok djm@

branches: 1.14.4; 1.14.6;
re-add rijndael-cbc@lysator.liu.se for MacSSH; ash@lab.poc.net

remove "rijndael-*", just use "aes-" since this how rijndael is called
in the drafts; ok stevesk@

branches: 1.12.2; 1.12.4;
switch to aes128-cbc/hmac-md5 by default in SSH2 -- faster; provos & markus ok

1) clean up the MAC support for SSH-2
2) allow you to specify the MAC with 'ssh -m'
3) or the 'MACs' keyword in ssh(d)_config
4) add hmac-{md5,sha1}-96
ok stevesk@, provos@

$OpenBSD$

add support for RSA to SSH2. please test.

there are now 3 types of keys: RSA1 is used by ssh-1 only,
RSA and DSA are used by SSH2.

you can use 'ssh-keygen -t rsa -f ssh2_rsa_file' to generate RSA
keys for SSH2 and use the RSA keys for hostkeys or for user keys.

SSH2 RSA or DSA keys are added to .ssh/authorised_keys2 as before.

IdentityFile2, HostDsaKey and DSAAuthentication are obsolete.
you can use multiple IdentityFile and HostKey for all types of keys.

the option DSAAuthentication is replaced by PubkeyAuthetication.

branches: 1.8.2;
prefer no compression

rijndael/aes support

new cipher framework

First rough implementation of the diffie-hellman group exchange. The
client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys. University of Windsor provided network, T the company.

cleanup copyright notices on all files. I have attempted to be accurate with
the details. everything is now under Tatu's licence (which I copied from his
readme), and/or the core-sdi bsd-ish thing for deattack, or various openbsd
developers under a 2-term bsd licence. We're not changing any rules, just
being accurate.

split kexinit/kexdh, factor out common code

branches: 1.2.2;
complain about invalid ciphers in SSH1 (e.g. arcfour is SSH2 only)

ssh2 client implementation, interops w/ ssh.com and lsh servers.

add the sntrup761x25519-sha512@openssh.com hybrid ECDH/x25519 +
Streamlined NTRU Prime post-quantum KEX to the default KEXAlgorithms
list (after the ECDH methods but before the prime-group DH ones).

ok markus@

After years of forewarning, disable the RSA/SHA-1 signature algorithm
by default. It is feasible to create colliding SHA1 hashes, so we
need to deprecate its use.

RSA/SHA-256/512 remains available and will be transparently selected
instead of RSA/SHA1 for most SSH servers released in the last five+
years. There is no need to regenerate RSA keys.

The use of RSA/SHA1 can be re-enabled by adding "ssh-rsa" to the
PubkeyAcceptedAlgorithms directives on the client and server.

ok dtucker deraadt

prefer ed25519 signature algorithm variants to ECDSA; ok markus@

remove ssh-rsa (SHA1) from the list of allowed CA signature algorithms
ok markus

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY

branches: 1.18.2; 1.18.4;
add a new compression method that delays compression until the user
has been authenticated successfully and set compression to 'delayed'
for sshd.

this breaks older openssh clients (< 3.5) if they insist on
compression, so you have to re-enable compression in sshd_config.
ok djm@

add support for draft-harris-ssh-arcfour-fixes-02 improved arcfour modes;
ok markus@

branches: 1.16.2; 1.16.4;
implement diffie-hellman-group14-sha1 kex method (trivial extension to
existing diffie-hellman-group1-sha1); ok markus@

branches: 1.15.2; 1.15.4;
experimental support for aes-ctr modes from
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-00.txt
ok djm@

branches: 1.14.4; 1.14.6;
re-add rijndael-cbc@lysator.liu.se for MacSSH; ash@lab.poc.net

remove "rijndael-*", just use "aes-" since this how rijndael is called
in the drafts; ok stevesk@

branches: 1.12.2; 1.12.4;
switch to aes128-cbc/hmac-md5 by default in SSH2 -- faster; provos & markus ok

1) clean up the MAC support for SSH-2
2) allow you to specify the MAC with 'ssh -m'
3) or the 'MACs' keyword in ssh(d)_config
4) add hmac-{md5,sha1}-96
ok stevesk@, provos@

$OpenBSD$

add support for RSA to SSH2. please test.

there are now 3 types of keys: RSA1 is used by ssh-1 only,
RSA and DSA are used by SSH2.

you can use 'ssh-keygen -t rsa -f ssh2_rsa_file' to generate RSA
keys for SSH2 and use the RSA keys for hostkeys or for user keys.

SSH2 RSA or DSA keys are added to .ssh/authorised_keys2 as before.

IdentityFile2, HostDsaKey and DSAAuthentication are obsolete.
you can use multiple IdentityFile and HostKey for all types of keys.

the option DSAAuthentication is replaced by PubkeyAuthetication.

branches: 1.8.2;
prefer no compression

rijndael/aes support

new cipher framework

First rough implementation of the diffie-hellman group exchange. The
client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys. University of Windsor provided network, T the company.

cleanup copyright notices on all files. I have attempted to be accurate with
the details. everything is now under Tatu's licence (which I copied from his
readme), and/or the core-sdi bsd-ish thing for deattack, or various openbsd
developers under a 2-term bsd licence. We're not changing any rules, just
being accurate.

split kexinit/kexdh, factor out common code

branches: 1.2.2;
complain about invalid ciphers in SSH1 (e.g. arcfour is SSH2 only)

ssh2 client implementation, interops w/ ssh.com and lsh servers.

After years of forewarning, disable the RSA/SHA-1 signature algorithm
by default. It is feasible to create colliding SHA1 hashes, so we
need to deprecate its use.

RSA/SHA-256/512 remains available and will be transparently selected
instead of RSA/SHA1 for most SSH servers released in the last five+
years. There is no need to regenerate RSA keys.

The use of RSA/SHA1 can be re-enabled by adding "ssh-rsa" to the
PubkeyAcceptedAlgorithms directives on the client and server.

ok dtucker deraadt

prefer ed25519 signature algorithm variants to ECDSA; ok markus@

remove ssh-rsa (SHA1) from the list of allowed CA signature algorithms
ok markus

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY

branches: 1.18.2; 1.18.4;
add a new compression method that delays compression until the user
has been authenticated successfully and set compression to 'delayed'
for sshd.

this breaks older openssh clients (< 3.5) if they insist on
compression, so you have to re-enable compression in sshd_config.
ok djm@

add support for draft-harris-ssh-arcfour-fixes-02 improved arcfour modes;
ok markus@

branches: 1.16.2; 1.16.4;
implement diffie-hellman-group14-sha1 kex method (trivial extension to
existing diffie-hellman-group1-sha1); ok markus@

branches: 1.15.2; 1.15.4;
experimental support for aes-ctr modes from
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-00.txt
ok djm@

branches: 1.14.4; 1.14.6;
re-add rijndael-cbc@lysator.liu.se for MacSSH; ash@lab.poc.net

remove "rijndael-*", just use "aes-" since this how rijndael is called
in the drafts; ok stevesk@

branches: 1.12.2; 1.12.4;
switch to aes128-cbc/hmac-md5 by default in SSH2 -- faster; provos & markus ok

1) clean up the MAC support for SSH-2
2) allow you to specify the MAC with 'ssh -m'
3) or the 'MACs' keyword in ssh(d)_config
4) add hmac-{md5,sha1}-96
ok stevesk@, provos@

$OpenBSD$

add support for RSA to SSH2. please test.

there are now 3 types of keys: RSA1 is used by ssh-1 only,
RSA and DSA are used by SSH2.

you can use 'ssh-keygen -t rsa -f ssh2_rsa_file' to generate RSA
keys for SSH2 and use the RSA keys for hostkeys or for user keys.

SSH2 RSA or DSA keys are added to .ssh/authorised_keys2 as before.

IdentityFile2, HostDsaKey and DSAAuthentication are obsolete.
you can use multiple IdentityFile and HostKey for all types of keys.

the option DSAAuthentication is replaced by PubkeyAuthetication.

branches: 1.8.2;
prefer no compression

rijndael/aes support

new cipher framework

First rough implementation of the diffie-hellman group exchange. The
client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys. University of Windsor provided network, T the company.

cleanup copyright notices on all files. I have attempted to be accurate with
the details. everything is now under Tatu's licence (which I copied from his
readme), and/or the core-sdi bsd-ish thing for deattack, or various openbsd
developers under a 2-term bsd licence. We're not changing any rules, just
being accurate.

split kexinit/kexdh, factor out common code

branches: 1.2.2;
complain about invalid ciphers in SSH1 (e.g. arcfour is SSH2 only)

ssh2 client implementation, interops w/ ssh.com and lsh servers.

prefer ed25519 signature algorithm variants to ECDSA; ok markus@

remove ssh-rsa (SHA1) from the list of allowed CA signature algorithms
ok markus

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY

branches: 1.18.2; 1.18.4;
add a new compression method that delays compression until the user
has been authenticated successfully and set compression to 'delayed'
for sshd.

this breaks older openssh clients (< 3.5) if they insist on
compression, so you have to re-enable compression in sshd_config.
ok djm@

add support for draft-harris-ssh-arcfour-fixes-02 improved arcfour modes;
ok markus@

branches: 1.16.2; 1.16.4;
implement diffie-hellman-group14-sha1 kex method (trivial extension to
existing diffie-hellman-group1-sha1); ok markus@

branches: 1.15.2; 1.15.4;
experimental support for aes-ctr modes from
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-00.txt
ok djm@

branches: 1.14.4; 1.14.6;
re-add rijndael-cbc@lysator.liu.se for MacSSH; ash@lab.poc.net

remove "rijndael-*", just use "aes-" since this how rijndael is called
in the drafts; ok stevesk@

branches: 1.12.2; 1.12.4;
switch to aes128-cbc/hmac-md5 by default in SSH2 -- faster; provos & markus ok

1) clean up the MAC support for SSH-2
2) allow you to specify the MAC with 'ssh -m'
3) or the 'MACs' keyword in ssh(d)_config
4) add hmac-{md5,sha1}-96
ok stevesk@, provos@

$OpenBSD$

add support for RSA to SSH2. please test.

there are now 3 types of keys: RSA1 is used by ssh-1 only,
RSA and DSA are used by SSH2.

you can use 'ssh-keygen -t rsa -f ssh2_rsa_file' to generate RSA
keys for SSH2 and use the RSA keys for hostkeys or for user keys.

SSH2 RSA or DSA keys are added to .ssh/authorised_keys2 as before.

IdentityFile2, HostDsaKey and DSAAuthentication are obsolete.
you can use multiple IdentityFile and HostKey for all types of keys.

the option DSAAuthentication is replaced by PubkeyAuthetication.

branches: 1.8.2;
prefer no compression

rijndael/aes support

new cipher framework

First rough implementation of the diffie-hellman group exchange. The
client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys. University of Windsor provided network, T the company.

cleanup copyright notices on all files. I have attempted to be accurate with
the details. everything is now under Tatu's licence (which I copied from his
readme), and/or the core-sdi bsd-ish thing for deattack, or various openbsd
developers under a 2-term bsd licence. We're not changing any rules, just
being accurate.

split kexinit/kexdh, factor out common code

branches: 1.2.2;
complain about invalid ciphers in SSH1 (e.g. arcfour is SSH2 only)

ssh2 client implementation, interops w/ ssh.com and lsh servers.

remove ssh-rsa (SHA1) from the list of allowed CA signature algorithms
ok markus

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY

branches: 1.18.2; 1.18.4;
add a new compression method that delays compression until the user
has been authenticated successfully and set compression to 'delayed'
for sshd.

this breaks older openssh clients (< 3.5) if they insist on
compression, so you have to re-enable compression in sshd_config.
ok djm@

add support for draft-harris-ssh-arcfour-fixes-02 improved arcfour modes;
ok markus@

branches: 1.16.2; 1.16.4;
implement diffie-hellman-group14-sha1 kex method (trivial extension to
existing diffie-hellman-group1-sha1); ok markus@

branches: 1.15.2; 1.15.4;
experimental support for aes-ctr modes from
http://www.ietf.org/internet-drafts/draft-ietf-secsh-newmodes-00.txt
ok djm@

branches: 1.14.4; 1.14.6;
re-add rijndael-cbc@lysator.liu.se for MacSSH; ash@lab.poc.net

remove "rijndael-*", just use "aes-" since this how rijndael is called
in the drafts; ok stevesk@

branches: 1.12.2; 1.12.4;
switch to aes128-cbc/hmac-md5 by default in SSH2 -- faster; provos & markus ok

1) clean up the MAC support for SSH-2
2) allow you to specify the MAC with 'ssh -m'
3) or the 'MACs' keyword in ssh(d)_config
4) add hmac-{md5,sha1}-96
ok stevesk@, provos@

$OpenBSD$

add support for RSA to SSH2. please test.

there are now 3 types of keys: RSA1 is used by ssh-1 only,
RSA and DSA are used by SSH2.

you can use 'ssh-keygen -t rsa -f ssh2_rsa_file' to generate RSA
keys for SSH2 and use the RSA keys for hostkeys or for user keys.

SSH2 RSA or DSA keys are added to .ssh/authorised_keys2 as before.

IdentityFile2, HostDsaKey and DSAAuthentication are obsolete.
you can use multiple IdentityFile and HostKey for all types of keys.

the option DSAAuthentication is replaced by PubkeyAuthetication.

branches: 1.8.2;
prefer no compression

rijndael/aes support

new cipher framework

First rough implementation of the diffie-hellman group exchange. The
client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys. University of Windsor provided network, T the company.

cleanup copyright notices on all files. I have attempted to be accurate with
the details. everything is now under Tatu's licence (which I copied from his
readme), and/or the core-sdi bsd-ish thing for deattack, or various openbsd
developers under a 2-term bsd licence. We're not changing any rules, just
being accurate.

split kexinit/kexdh, factor out common code

branches: 1.2.2;
complain about invalid ciphers in SSH1 (e.g. arcfour is SSH2 only)

ssh2 client implementation, interops w/ ssh.com and lsh servers.

Remove unsupported algorithms from list of defaults at run time and
remove ifdef and distinct settings for OPENSSL=no case.

This will make things much simpler for -portable where the exact set
of algos depends on the configuration of both OpenSSH and the libcrypto
it's linked against (if any). ok djm@

remove diffie-hellman-group14-sha1 from default kex to see what happens.
general mostly ok

sort sk-* methods behind their plain key methods cousins for now

allow security keys to act as host keys as well as user keys.

Previously we didn't do this because we didn't want to expose
the attack surface presented by USB and FIDO protocol handling,
but now that this is insulated behind ssh-sk-helper there is
less risk.

ok markus@

add security key types to list of keys allowed to act as CAs;
spotted by Ron Frederick

enable ed25519 support; ok djm

remove duplicate PUBKEY_DEFAULT_PK_ALG on !WITH_OPENSSL path

Separate myproposal.h userauth pubkey types

U2F/FIDO keys are not supported for host authentication, so we need
a separate list for user keys.

feedback & ok markus@

openssh-7.9 accidentally reused the server's algorithm lists in the
client for KEX, ciphers and MACs. The ciphers and MACs were
identical between the client and server, but the error accidentially
disabled the diffie-hellman-group-exchange-sha1 KEX method.

This fixes the client code to use the correct method list, but
because nobody complained, it also disables the
diffie-hellman-group-exchange-sha1 KEX method.

Reported by nuxi AT vault24.org via bz#2697; ok dtucker

add SSH_ALLOWED_CA_SIGALGS - the default list of signature algorithms
that are allowed for CA signatures. Notably excludes ssh-dsa.

ok markus@

Improve strictness and control over RSA-SHA2 signature types:

In ssh, when an agent fails to return a RSA-SHA2 signature when
requested and falls back to RSA-SHA1 instead, retry the signature to
ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
matches the one in the signature itself.

In sshd, strictly enforce that the public key algorithm sent in the
SSH_MSG_USERAUTH message matches what appears in the signature.

Make the sshd_config PubkeyAcceptedKeyTypes and
HostbasedAcceptedKeyTypes options control accepted signature algorithms
(previously they selected supported key types). This allows these
options to ban RSA-SHA1 in favour of RSA-SHA2.

Add new signature algorithms "rsa-sha2-256-cert-v01@openssh.com" and
"rsa-sha2-512-cert-v01@openssh.com" to force use of RSA-SHA2 signatures
with certificate keys.

feedback and ok markus@

Don't offer CBC ciphers by default in the client. ok markus@

Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

support plain curve25519-sha256 KEX algorithm now that it is
approaching standardisation (same algorithm is currently supported
as curve25519-sha256@libssh.org)

remove 3des-cbc from the client's default proposal; 64-bit block ciphers
are not safe in 2016 and we don't want to wait until attacks like sweet32
are extended to SSH.

As 3des-cbc was the only mandatory cipher in the SSH RFCs, this may
cause problems connecting to older devices using the defaults, but
it's highly likely that such devices already need explicit
configuration for KEX and hostkeys anyway.

ok deraadt, markus, dtucker

add support for additional fixed DH groups from
draft-ietf-curdle-ssh-kex-sha2-03

diffie-hellman-group14-sha256 (2K group)
diffie-hellman-group16-sha512 (4K group)
diffie-hellman-group18-sha512 (8K group)

based on patch from Mark D. Baushke and Darren Tucker
ok markus@

turn off more old crypto in the client: hmac-md5, ripemd, truncated
HMACs, RC4, blowfish. ok markus@ dtucker@

prefer rsa-sha2-512 over -256 for hostkeys, too; noticed by naddy@

implement SHA2-{256,512} for RSASSA-PKCS1-v1_5 signatures (user and host auth)
based on draft-rsa-dsa-sha2-256-03.txt and draft-ssh-ext-info-04.txt;
with & ok djm@

Turn off DSA by default; add HostKeyAlgorithms to the server and
PubkeyAcceptedKeyTypes to the client side, so it still can be
tested or turned back on; feedback and ok djm@

turn off 1024 bit diffie-hellman-group1-sha1 key exchange method
(already off in server, this turns it off in the client by default too)
ok dtucker@

delete support for legacy v00 certificates; "sure" markus@ dtucker@

Reorder client proposal to prefer diffie-hellman-group-exchange-sha1 over
diffie-hellman-group14-sha1. ok djm@

Add back a backslash removed in rev 1.42 so KEX_SERVER_ENCRYPT will
include aes again.

ok deraadt@

promote chacha20-poly1305@openssh.com to be the default cipher;
ok markus

by popular demand, add back hamc-sha1 to server proposal for better compat
with many clients still in use. ok deraadt

UMAC can use our local fallback implementation of AES when OpenSSL isn't
available. Glue code straight from Ted Krovetz's original umac.c.
ok markus@

make compiling against OpenSSL optional (make OPENSSL=no);
reduces algorithms to curve25519, aes-ctr, chacha, ed25519;
allows us to explore further options; with and ok djm

disable weak proposals in sshd, but keep them in ssh; ok djm@

The current sharing of myproposal[] between both client and server code
makes the previous diff highly unpallatable. We want to go in that
direction for the server, but not for the client. Sigh.
Brought up by naddy.

trimm default proposals.

This commit removes the weaker pre-SHA2 hashes, the broken ciphers
(arcfour), and the broken modes (CBC) from the default configuration
(the patch only changes the default, all the modes are still available
for the config files).

ok djm@, reminded by tedu@ & naddy@ and discussed with many

support ed25519 keys (hostkeys and user identities) using the public domain
ed25519 reference code from SUPERCOP, see http://ed25519.cr.yp.to/software.html
feedback, help & ok djm@

Add a new protocol 2 transport cipher "chacha20-poly1305@openssh.com"
that combines Daniel Bernstein's ChaCha20 stream cipher and Poly1305 MAC
to build an authenticated encryption mode.

Inspired by and similar to Adam Langley's proposal for TLS:
http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03
but differs in layout used for the MAC calculation and the use of a
second ChaCha20 instance to separately encrypt packet lengths.
Details are in the PROTOCOL.chacha20poly1305 file.

Feedback markus@, naddy@; manpage bits Loganden Velvindron @ AfriNIC
ok markus@ naddy@

use curve25519 for default key exchange (curve25519-sha256@libssh.org);
initial patch from Aris Adamantiadis; ok djm@

support AES-GCM as defined in RFC 5647 (but with simpler KEX handling)
ok and feedback djm@

add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms
that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

add umac128 variant; ok djm@ at n2k12

Remove hmac-sha2-256-96 and hmac-sha2-512-96 MACs since they were removed
from draft6 of the spec and will not be in the RFC when published. Patch
from mdb at juniper net via bz#2023, ok markus.

Add new SHA256 and SHA512 based HMAC modes from
http://www.ietf.org/id/draft-dbider-sha2-mac-for-ssh-02.txt

feedback and ok markus@

prefer ECDH in a 256 bit curve field; prompted by naddy@

Implement Elliptic Curve Cryptography modes for key exchange (ECDH) and
host/user keys (ECDSA) as specified by RFC5656. ECDH and ECDSA offer
better performance than plain DH and DSA at the same equivalent symmetric
key length, as well as much shorter keys.

Only the mandatory sections of RFC5656 are implemented, specifically the
three REQUIRED curves nistp256, nistp384 and nistp521 and only ECDH and
ECDSA. Point compression (optional in RFC5656 is NOT implemented).

Certificate host and user keys using the new ECDSA key types are supported.

Note that this code has not been tested for interoperability and may be
subject to change.

feedback and ok markus@

revised certificate format ssh-{dss,rsa}-cert-v01@openssh.com with the
following changes:

move the nonce field to the beginning of the certificate where it can
better protect against chosen-prefix attacks on the signature hash

Rename "constraints" field to "critical options"

Add a new non-critical "extensions" field

Add a serial number

The older format is still support for authentication and cert generation
(use "ssh-keygen -t v00 -s ca_key ..." to generate a v00 certificate)

ok markus@

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

prefer CTR modes and revised arcfour (i.e w/ discard) modes to CBC
modes; ok markus@

Add a new MAC algorithm for data integrity, UMAC-64 (not default yet, must
specify umac-64@openssh.com). Provides about 20% end-to-end speedup
compared to hmac-md5. Represents a different approach to message
authentication to that of HMAC that may be beneficial if HMAC based on one
of its underlying hash algorithms is found to be vulnerable to a new attack.
http://www.ietf.org/rfc/rfc4418.txt

in conjunction with and OK djm@

standardise spacing in $OpenBSD$ tags; requested by deraadt@

spacing

Implement the diffie-hellman-group-exchange-sha256 key exchange method
using the SHA256 code in libc (and wrapper to make it into an OpenSSL
EVP), interop tested against CVS PuTTY