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AES.h
1 /* AES - Advanced Encryption Standard
2
3 source version 1.0, June, 2005
4
5 Copyright (C) 2000-2005 Chris Lomont
6
7 This software is provided 'as-is', without any express or implied
8 warranty. In no event will the author be held liable for any damages
9 arising from the use of this software.
10
11 Permission is granted to anyone to use this software for any purpose,
12 including commercial applications, and to alter it and redistribute it
13 freely, subject to the following restrictions:
14
15 1. The origin of this software must not be misrepresented; you must not
16 claim that you wrote the original software. If you use this software
17 in a product, an acknowledgment in the product documentation would be
18 appreciated but is not required.
19 2. Altered source versions must be plainly marked as such, and must not be
20 misrepresented as being the original software.
21 3. This notice may not be removed or altered from any source distribution.
22
23 Chris Lomont
24 chris@lomont.org
25
26 The AES Standard is maintained by NIST
27 http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
28
29 This legalese is patterned after the zlib compression library
30 */
31
32 // headed to implement Advanced Encryption Standard - Rijndael2
33 #ifndef _AES_H
34 #define _AES_H
35
36 /* USAGE:
37 1. Create a AES class (or more as necessary)
38 2. Call class method SetParameters
39 3. To encrypt, call method StartEncryption with the key, and then
40 call method Encrypt with enough space to store the proper size blocks.
41 4. To decrypt, call method StartDecryption with the key, and then
42 call method Decrypt with enough space to store the proper size blocks.
43
44 Alternatively, you can call EncryptBlock and DecryptBlock block to process blocksize
45 (default to 16 bytes) bytes at a time. It is recommended to use the Encrypt function
46 for multiple block encryption since it uses chaining modes that make the overall
47 stream much more secure than the default block based encryption, which by default would
48 be mode ECB.
49
50 EXAMPLE: want to encrypt 37 bytes of data with 192 bit key, which will use 3 16 byte blocks
51 AES aes;
52 aes.SetParameters(192);
53 aes.StartEncryption(key);
54 aes.Encrypt(data,output,3); // note data and output must be at least 48 bytes!
55 */
56
57 // todo - replace all types with u1byte, u4byte, etc
58
59 class GD_API AES
60 {
61 public:
62 // the constructor - makes sure local things are initialized
63 // it if fails, throws the string "Tables failed to initialize"
64 AES(void);
65
66 // multiple block encryption/decryption modes
67 // See http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
68 enum BlockMode {
69 ECB = 0, // Electronic CodeBook - each block independent, weak
70 CBC = 1 // Cipher Block Chaining - most secure
71 // todo - CFB = 2, // Cipher FeedBack - secure
72 // todo - OFB = 3, // Output FeedBack - secure
73 // todo - CTR = 4, // Counter - allows midstream decryption, somewhat secure
74 // todo - EAX = 5, - http://www.cs.berkeley.edu/~daw/papers/eprint-short-ae.pdf
75 // todo - GCM = 6, - http://www.cryptobarn.com/papers/gcm-spec.pdf
76 };
77
78 // block and key size are in bits, legal values are 128, 192, and 256 independently.
79 // NOTE: the AES standard only uses a blocksize of 128, so we default to that
80 void SetParameters(int keylength, int blocklength = 128);
81
82 // call this before any encryption with the key to use
83 void StartEncryption(const unsigned char * key);
84 // encrypt a single block (default 128 bits, or unsigned char[16]) of data
85 void EncryptBlock(const unsigned char * datain, unsigned char * dataout);
86 // Call this to encrypt any length data. Note the size is in BLOCKS, so you must
87 // have enough space in datain and dataout to accomodate this. Pad your data before
88 // calling, preferably using the padding methods listed below.
89 // Decryption must use the same mode as the encryption.
90 void Encrypt(const unsigned char * datain, unsigned char * dataout, unsigned long numBlocks, BlockMode mode = CBC);
91
92 // call this before any decryption with the key to use
93 void StartDecryption(const unsigned char * key);
94 // decrypt a single block (default 128 bits, or unsigned char[16]) of data
95 void DecryptBlock(const unsigned char * datain, unsigned char * dataout);
96 // Call this to decrypt any length data. Note the size is in BLOCKS, so you must
97 // have enough space in datain and dataout to accomodate this. Pad your data before
98 // calling, preferably using the padding methods listed below. You must know the desired
99 // length of the output data, since all the blocks are returned decrypted.
100 // Encryption must use the same mode as the decryption.
101 void Decrypt(const unsigned char * datain, unsigned char * dataout, unsigned long numBlocks, BlockMode mode = CBC);
102
103 private:
104
105 int Nb,Nk; // block and key length / 32, should be 4,6,or 8
106 int Nr; // number of rounds
107
108 unsigned char W[4*8*15]; // the expanded key
109
110 // Key expansion code - makes local copy
111 void KeyExpansion(const unsigned char * key);
112
113 }; // class AES
114
115
116 /* PADDING:
117 The AES (Rijndael) encryption algorithm pads encrypted data to a multiple of 16 bytes by default.
118 Other blocksizes are similar. Methods:
119 1. RFC 1423 padding scheme:
120 Each padding byte is set to the number of padding bytes. If the data is already a multiple
121 of 16 bytes, 16 additional bytes are added, each having the value 0x10.
122 2. FIPS81 (Federal Information Processing Standards 81):
123 The last byte contains the number of padding bytes, including itself,
124 and the other padding bytes are set to random values.
125 3. Each padding byte is set to a random value. The decryptor must know how many bytes are in the original unencrypted data.
126 */
127
128 /* TODO
129 The Encrypt() function is used to encrypt larger blocks of data. The block size has to be a multiple of the method's block size.
130 This function can operate in the following modes: ECB, CBC or CFB. ECB mode is not using chaining. If the same block is encrypted
131 twice with the same key, the resulting ciphertext blocks are the same. In CBC mode, a ciphertext block is obtained by first XORing
132 the plaintext block with the previous ciphertext block, and encrypting the resulting value. In CFB mode, a ciphertext block is
133 obtained by encrypting the previous ciphertext block and XORing the resulting value with the plaintext. The operation mode is
134 specified in the iMode parameter with ECB being the default value.
135
136 */
137
138 #endif // _AES_H
139 // end - AES.h
140