diff options
| -rw-r--r-- | aes_cbc.c | 85 |
1 files changed, 46 insertions, 39 deletions
@@ -1,6 +1,6 @@ /* -This is an implementation of the AES128 algorithm, specifically ECB mode. +This is an implementation of the AES128 algorithm, specifically ECB and CBC mode. The implementation is verified against the test vectors in: National Institute of Standards and Technology Special Publication 800-38A 2001 ED @@ -46,7 +46,7 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0) // The number of 32 bit words in a key. #define Nk 4 // Key length in bytes [128 bit] -#define keyln 16 +#define KEYLEN 16 // The number of rounds in AES Cipher. #define Nr 10 @@ -57,13 +57,6 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0) #define MULTIPLY_AS_A_FUNCTION 0 #endif -#ifndef CBC - #define CBC 1 -#endif - -#ifndef ECB - #define ECB 0 -#endif /*****************************************************************************/ /* Private variables: */ @@ -439,10 +432,10 @@ static void InvCipher(void) AddRoundKey(0); } -static void BufferCopy(uint8_t* output, uint8_t* input) +static void BlockCopy(uint8_t* output, uint8_t* input) { uint8_t i; - for (i=0;i<16;++i) + for (i=0;i<KEYLEN;++i) { output[i] = input[i]; } @@ -459,7 +452,7 @@ static void BufferCopy(uint8_t* output, uint8_t* input) void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t* output) { // Copy input to output, and work in-memory on output - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; Key = key; @@ -472,7 +465,7 @@ void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t* output) void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t *output) { // Copy input to output, and work in-memory on output - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; // The KeyExpansion routine must be called before encryption. @@ -495,74 +488,88 @@ void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t *output) static void XorWithIv(uint8_t* buf) { uint8_t i; - for(i = 0; i < 16; ++i) + for(i = 0; i < KEYLEN; ++i) { buf[i] ^= Iv[i]; } } -void AES128_CBC_encrypt_buffer(uint8_t* input, uint32_t length, const uint8_t* key, uint8_t* output, const uint8_t* iv) +void AES128_CBC_encrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv) { intptr_t i; - uint8_t j; - uint8_t remainders = length % 16; /* Remaining bytes in the last non-full block */ + uint8_t remainders = length % KEYLEN; /* Remaining bytes in the last non-full block */ - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; - Key = key; - KeyExpansion(); + // Skip the key expansion if key is passed as 0 + if(0 != key) + { + Key = key; + KeyExpansion(); + } - Iv = (uint8_t*)iv; + if(iv != 0) + { + Iv = (uint8_t*)iv; + } - for(i = 0; i < length; i += 16) + for(i = 0; i < length; i += KEYLEN) { XorWithIv(input); - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; Cipher(); Iv = output; - input += 16; - output += 16; + input += KEYLEN; + output += KEYLEN; } if(remainders) { - BufferCopy(output, input); - memset(output + remainders, 0, 16 - remainders); /* add 0-padding */ + BlockCopy(output, input); + memset(output + remainders, 0, KEYLEN - remainders); /* add 0-padding */ state = (state_t*)output; Cipher(); } } -void AES128_CBC_decrypt_buffer(uint8_t* input, uint32_t length, const uint8_t* key, uint8_t* output, const uint8_t* iv) +void AES128_CBC_decrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv) { intptr_t i; - uint8_t remainders = length % 16; /* Remaining bytes in the last non-full block */ + uint8_t remainders = length % KEYLEN; /* Remaining bytes in the last non-full block */ - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; - Key = key; - KeyExpansion(); + // Skip the key expansion if key is passed as 0 + if(0 != key) + { + Key = key; + KeyExpansion(); + } - Iv = (uint8_t*)iv; + // If iv is passed as 0, we continue to encrypt without re-setting the Iv + if(iv != 0) + { + Iv = (uint8_t*)iv; + } - for(i = 0; i < length; i += 16) + for(i = 0; i < length; i += KEYLEN) { - BufferCopy(output, input); + BlockCopy(output, input); state = (state_t*)output; InvCipher(); XorWithIv(output); Iv = input; - input += 16; - output += 16; + input += KEYLEN; + output += KEYLEN; } if(remainders) { - BufferCopy(output, input); - memset(output+remainders, 0, 16-remainders); /* add 0-padding */ + BlockCopy(output, input); + memset(output+remainders, 0, KEYLEN - remainders); /* add 0-padding */ state = (state_t*)output; InvCipher(); } |