1aes(n) Advanced Encryption Standard (AES) aes(n)
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6
8 aes - Implementation of the AES block cipher
9
11 package require Tcl 8.2
12 package require aes ?1.0?
14 ::aes::aes ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv
16 vector? ?-hex? ?-out channel? ?-chunksize size? [ -in channel | data ]
17 ::aes::Init mode keydata iv
19 ::aes::Encrypt Key data
21 ::aes::Decrypt Key data
23 ::aes::Reset Key iv
25 ::aes::Final Key
27_________________________________________________________________
29
31 This is an implementation in Tcl of the Advanced Encryption Standard
32 (AES) as published by the U.S. National Institute of Standards and
33 Technology [1]. AES is a 128-bit block cipher with a variable key size
34 of 128, 192 or 256 bits. This implementation supports ECB and CBC
35 modes.
36
38 ::aes::aes ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv
39 vector? ?-hex? ?-out channel? ?-chunksize size? [ -in channel | data ]
40 Perform the aes algorithm on either the data provided by the
41 argument or on the data read from the -in channel. If an -out
42 channel is given then the result will be written to this chan‐
43 nel.
44 The -key option must be given. This parameter takes a binary
46 string of either 16, 24 or 32 bytes in length and is used to
47 generate the key schedule.
48 The -mode and -dir options are optional and default to cbc mode
50 and encrypt respectively. The initialization vector -iv takes a
51 16 byte binary argument which defaults to all zeros. See MODES
52 OF OPERATION for more about available modes and their uses.
53 AES is a 128-bit block cipher. This means that the data must be
55 provided in units that are a multiple of 16 bytes.
56
58 Internal state is maintained in an opaque structure that is returned
59 from the Init function. In ECB mode the state is not affected by the
60 input but for CBC mode some input dependent state is maintained and may
61 be reset by calling the Reset function with a new initialization vector
62 value.
63 ::aes::Init mode keydata iv
65 Construct a new AES key schedule using the specified key data
66 and the given initialization vector. The initialization vector
67 is not used with ECB mode but is important for CBC mode. See
68 MODES OF OPERATION for details about cipher modes.
69 ::aes::Encrypt Key data
71 Use a prepared key acquired by calling Init to encrypt the pro‐
72 vided data. The data argument should be a binary array that is a
73 multiple of the AES block size of 16 bytes. The result is a
74 binary array the same size as the input of encrypted data.
75 ::aes::Decrypt Key data
77 Decipher data using the key. Note that the same key may be used
78 to encrypt and decrypt data provided that the initialization
79 vector is reset appropriately for CBC mode.
80 ::aes::Reset Key iv
82 Reset the initialization vector. This permits the programmer to
83 re-use a key and avoid the cost of re-generating the key sched‐
84 ule where the same key data is being used multiple times.
85 ::aes::Final Key
87 This should be called to clean up resources associated with Key.
88 Once this function has been called the key may not be used
89 again.
90
92 Electronic Code Book (ECB)
93 ECB is the basic mode of all block ciphers. Each block is
94 encrypted independently and so identical plain text will produce
95 identical output when encrypted with the same key. Any encryp‐
96 tion errors will only affect a single block however this is vul‐
97 nerable to known plaintext attacks.
98 Cipher Block Chaining (CBC)
100 CBC mode uses the output of the last block encryption to affect
101 the current block. An initialization vector of the same size as
102 the cipher block size is used to handle the first block. The
103 initialization vector should be chosen randomly and transmitted
104 as the first block of the output. Errors in encryption affect
105 the current block and the next block after which the cipher will
106 correct itself. CBC is the most commonly used mode in software
107 encryption.
108
110 % set nil_block [string repeat \\0 16]
111 % aes::aes -hex -mode cbc -dir encrypt -key $nil_block $nil_block
112 66e94bd4ef8a2c3b884cfa59ca342b2e
113 set Key [aes::Init cbc $sixteen_bytes_key_data $sixteen_byte_iv]
116 append ciphertext [aes::Encrypt $Key $plaintext]
117 append ciphertext [aes::Encrypt $Key $additional_plaintext]
118 aes::Final $Key
119
122 [1] "Advanced Encryption Standard", Federal Information Processing
123 Standards Publication 197, 2001 (http://csrc.nist.gov/publica‐
124 tions/fips/fips197/fips-197.pdf)
125
127 Thorsten Schloermann, Pat Thoyts
128
130 blowfish(n), des(n), md5(n), sha1(n)
131
133 aes, block cipher, data integrity, encryption, security
134
136 Copyright (c) 2005, Pat Thoyts <patthoyts@users.sourceforge.net>
137aes 1.0 aes(n)