1=pod
2
3=head1 NAME
4
5PKCS7_sign - create a PKCS#7 signedData structure
6
7=head1 SYNOPSIS
8
9 #include <openssl/pkcs7.h>
10
11 PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
12
13=head1 DESCRIPTION
14
15PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert>
16is the certificate to sign with, B<pkey> is the corresponsding private key.
17B<certs> is an optional additional set of certificates to include in the
18PKCS#7 structure (for example any intermediate CAs in the chain). 
19
20The data to be signed is read from BIO B<data>.
21
22B<flags> is an optional set of flags.
23
24=head1 NOTES
25
26Any of the following flags (ored together) can be passed in the B<flags> parameter.
27
28Many S/MIME clients expect the signed content to include valid MIME headers. If
29the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
30to the data.
31
32If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
33PKCS7 structure, the signer's certificate must still be supplied in the B<signcert>
34parameter though. This can reduce the size of the signature if the signers certificate
35can be obtained by other means: for example a previously signed message.
36
37The data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED> 
38is set in which case it is omitted. This is used for PKCS7 detached signatures
39which are used in S/MIME plaintext signed messages for example.
40
41Normally the supplied content is translated into MIME canonical format (as required
42by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This
43option should be used if the supplied data is in binary format otherwise the translation
44will corrupt it.
45
46The signedData structure includes several PKCS#7 autenticatedAttributes including
47the signing time, the PKCS#7 content type and the supported list of ciphers in
48an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes
49will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are
50omitted.
51
52If present the SMIMECapabilities attribute indicates support for the following
53algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any
54of these algorithms is disabled then it will not be included.
55
56If the flags B<PKCS7_PARTSIGN> is set then the returned B<PKCS7> structure
57is just initialized ready to perform the signing operation. The signing
58is however B<not> performed and the data to be signed is not read from
59the B<data> parameter. Signing is deferred until after the data has been
60written. In this way data can be signed in a single pass. Currently the
61flag B<PKCS7_DETACHED> B<must> also be set.
62
63=head1 NOTES
64
65Currently the flag B<PKCS7_PARTSIGN> is only supported for detached
66data. If this flag is set the returned B<PKCS7> structure is B<not>
67complete and outputting its contents via a function that does not
68properly finalize the B<PKCS7> structure will give unpredictable 
69results.
70
71At present only the SMIME_write_PKCS7() function properly finalizes the
72structure.
73
74=head1 BUGS
75
76PKCS7_sign() is somewhat limited. It does not support multiple signers, some
77advanced attributes such as counter signatures are not supported.
78
79The SHA1 digest algorithm is currently always used.
80
81When the signed data is not detached it will be stored in memory within the
82B<PKCS7> structure. This effectively limits the size of messages which can be
83signed due to memory restraints. There should be a way to sign data without
84having to hold it all in memory, this would however require fairly major
85revisions of the OpenSSL ASN1 code.
86
87
88=head1 RETURN VALUES
89
90PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred.
91The error can be obtained from ERR_get_error(3).
92
93=head1 SEE ALSO
94
95L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)>
96
97=head1 HISTORY
98
99PKCS7_sign() was added to OpenSSL 0.9.5
100
101The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8
102
103=cut
104