1[comment {-*- tcl -*- doctools manpage}]
2[manpage_begin aes n 1.0.2]
3[copyright {2005, Pat Thoyts <patthoyts@users.sourceforge.net>}]
4[moddesc {Advanced Encryption Standard (AES)}]
5[titledesc {Implementation of the AES block cipher}]
6[category  {Hashes, checksums, and encryption}]
7[require Tcl 8.2]
8[require aes [opt 1.0.2]]
9[description]
10[para]
11
12This is an implementation in Tcl of the Advanced Encryption Standard
13(AES) as published by the U.S. National Institute of Standards and
14Technology [lb]1[rb]. AES is a 128-bit block cipher with a variable
15key size of 128, 192 or 256 bits. This implementation supports ECB and
16CBC modes.
17
18[section {COMMANDS}]
19
20[list_begin definitions]
21
22[call [cmd "::aes::aes"] \
23        [opt [arg "-mode [lb]ecb|cbc[rb]"]] \
24        [opt [arg "-dir [lb]encrypt|decrypt[rb]"]] \
25        [arg "-key keydata"] \
26        [opt [arg "-iv vector"]] \
27        [opt [arg "-hex"]] \
28        [opt [arg "-out channel"]] \
29        [opt [arg "-chunksize size"]] \
30        [lb] [arg "-in channel"] | \
31        [arg "data"] [rb]]
32
33Perform the [package aes] algorithm on either the data provided
34by the argument or on the data read from the [arg "-in"] channel. If
35an [arg "-out"] channel is given then the result will be written to
36this channel.
37
38[para]
39
40The [arg -key] option must be given. This parameter takes a binary
41string of either 16, 24 or 32 bytes in length and is used to generate the 
42key schedule.
43
44[para]
45
46The [arg -mode] and [arg -dir] options are optional and default to cbc
47mode and encrypt respectively. The initialization vector [arg -iv]
48takes a 16 byte binary argument which defaults to all zeros.
49See [sectref "MODES OF OPERATION"] for more about available modes and
50their uses.
51
52[para]
53
54AES is a 128-bit block cipher. This means that the data must be
55provided in units that are a multiple of 16 bytes.
56
57[list_end]
58
59[section "PROGRAMMING INTERFACE"]
60
61Internal state is maintained in an opaque structure that is returned
62from the [cmd Init] function. In ECB mode the state is not affected by
63the input but for CBC mode some input dependent state is maintained
64and may be reset by calling the [cmd Reset] function with a new
65initialization vector value.
66
67[list_begin definitions]
68
69[call [cmd "::aes::Init"] [arg "mode"] [arg "keydata"] [arg "iv"]]
70
71Construct a new AES key schedule using the specified key data and the
72given initialization vector. The initialization vector is not used
73with ECB mode but is important for CBC mode.
74See [sectref "MODES OF OPERATION"] for details about cipher modes.
75
76[call [cmd "::aes::Encrypt"] [arg "Key"] [arg "data"]]
77
78Use a prepared key acquired by calling [cmd Init] to encrypt the
79provided data. The data argument should be a binary array that is a
80multiple of the AES block size of 16 bytes. The result is a binary
81array the same size as the input of encrypted data.
82
83[call [cmd "::aes::Decrypt"] [arg "Key"] [arg "data"]]
84
85Decipher data using the key. Note that the same key may be used to
86encrypt and decrypt data provided that the initialization vector is
87reset appropriately for CBC mode.
88
89[call [cmd "::aes::Reset"] [arg "Key"] [arg "iv"]]
90
91Reset the initialization vector. This permits the programmer to re-use
92a key and avoid the cost of re-generating the key schedule where the
93same key data is being used multiple times.
94
95[call [cmd "::aes::Final"] [arg "Key"]]
96
97This should be called to clean up resources associated with [arg Key].
98Once this function has been called the key may not be used again.
99
100[list_end]
101
102[section "MODES OF OPERATION"]
103
104[list_begin definitions]
105
106[def "Electronic Code Book (ECB)"]
107ECB is the basic mode of all block ciphers. Each block is encrypted
108independently and so identical plain text will produce identical
109output when encrypted with the same key. Any encryption errors will
110only affect a single block however this is vulnerable to known
111plaintext attacks.
112
113[def "Cipher Block Chaining (CBC)"]
114
115CBC mode uses the output of the last block encryption to affect the
116current block. An initialization vector of the same size as the cipher
117block size is used to handle the first block. The initialization
118vector should be chosen randomly and transmitted as the first block of
119the output. Errors in encryption affect the current block and the next
120block after which the cipher will correct itself. CBC is the most
121commonly used mode in software encryption. This is the default mode
122of operation for this module.
123
124[list_end]
125
126[section "EXAMPLES"]
127
128[example {
129% set nil_block [string repeat \\0 16]
130% aes::aes -hex -mode cbc -dir encrypt -key $nil_block $nil_block
13166e94bd4ef8a2c3b884cfa59ca342b2e
132}]
133
134[example {
135set Key [aes::Init cbc $sixteen_bytes_key_data $sixteen_byte_iv]
136append ciphertext [aes::Encrypt $Key $plaintext]
137append ciphertext [aes::Encrypt $Key $additional_plaintext]
138aes::Final $Key
139}]
140
141[section "REFERENCES"]
142
143[list_begin enumerated]
144
145[enum]
146    "Advanced Encryption Standard",
147    Federal Information Processing Standards Publication 197, 2001
148    ([uri http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf])
149
150[list_end]
151
152[see_also des(n) md5(n) sha1(n) blowfish(n)]
153
154[section AUTHORS]
155Thorsten Schloermann, Pat Thoyts
156
157[section {BUGS, IDEAS, FEEDBACK}]
158
159This document, and the package it describes, will undoubtedly contain
160bugs and other problems.
161
162Please report such in the category [emph aes] of the
163[uri {http://sourceforge.net/tracker/?group_id=12883} {Tcllib SF Trackers}].
164
165Please also report any ideas for enhancements you may have for either
166package and/or documentation.
167
168
169[keywords aes {block cipher} security encryption {data integrity}]
170[manpage_end]
171