diff options
Diffstat (limited to 'aes.c')
| -rw-r--r-- | aes.c | 128 |
1 files changed, 119 insertions, 9 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 @@ -34,6 +34,7 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0) /* Includes: */ /*****************************************************************************/ #include <stdint.h> +#include <string.h> // CBC mode, for memset #include "aes.h" @@ -45,7 +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 @@ -56,6 +57,7 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0) #define MULTIPLY_AS_A_FUNCTION 0 #endif + /*****************************************************************************/ /* Private variables: */ /*****************************************************************************/ @@ -69,6 +71,9 @@ static uint8_t RoundKey[176]; // The Key input to the AES Program static const uint8_t* Key; +// Initial Vector used for CBC mode etc. +static uint8_t* Iv; + // The lookup-tables are marked const so they can be placed in read-only storage instead of RAM // The numbers below can be computed dynamically trading ROM for RAM - // This can be useful in (embedded) bootloader applications, where ROM is often limited. @@ -333,7 +338,7 @@ static void InvMixColumns(void) } -// The SubBytes function substitutes the values in the +// The SubBytes Function Substitutes the values in the // state matrix with values in an S-box. static void InvSubBytes(void) { @@ -427,11 +432,10 @@ static void InvCipher(void) AddRoundKey(0); } -// This can be replaced with a call to memcpy -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]; } @@ -442,14 +446,15 @@ static void BufferCopy(uint8_t* output, uint8_t* input) /*****************************************************************************/ /* Public functions: */ /*****************************************************************************/ +#if defined(ECB) && ECB + 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; - // The KeyExpansion routine must be called before encryption. Key = key; KeyExpansion(); @@ -460,12 +465,117 @@ 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. Key = key; KeyExpansion(); InvCipher(); } + +#endif // #if defined(ECB) && ECB + + + + + +#if defined(CBC) && CBC + + +static void XorWithIv(uint8_t* buf) +{ + uint8_t i; + for(i = 0; i < KEYLEN; ++i) + { + buf[i] ^= Iv[i]; + } +} + +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 remainders = length % KEYLEN; /* Remaining bytes in the last non-full block */ + + BlockCopy(output, input); + state = (state_t*)output; + + // Skip the key expansion if key is passed as 0 + if(0 != key) + { + Key = key; + KeyExpansion(); + } + + if(iv != 0) + { + Iv = (uint8_t*)iv; + } + + for(i = 0; i < length; i += KEYLEN) + { + XorWithIv(input); + BlockCopy(output, input); + state = (state_t*)output; + Cipher(); + Iv = output; + input += KEYLEN; + output += KEYLEN; + } + + if(remainders) + { + BlockCopy(output, input); + memset(output + remainders, 0, KEYLEN - remainders); /* add 0-padding */ + state = (state_t*)output; + Cipher(); + } +} + +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 % KEYLEN; /* Remaining bytes in the last non-full block */ + + BlockCopy(output, input); + state = (state_t*)output; + + // Skip the key expansion if key is passed as 0 + if(0 != key) + { + Key = key; + KeyExpansion(); + } + + // 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 += KEYLEN) + { + BlockCopy(output, input); + state = (state_t*)output; + InvCipher(); + XorWithIv(output); + Iv = input; + input += KEYLEN; + output += KEYLEN; + } + + if(remainders) + { + BlockCopy(output, input); + memset(output+remainders, 0, KEYLEN - remainders); /* add 0-padding */ + state = (state_t*)output; + InvCipher(); + } +} + + +#endif // #if defined(CBC) && CBC + + |