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Made the key const, since it could be in ROM. Made 'Multiply' a function... #3

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Made the key const, since it could be in ROM. Made 'Multiply' a function... #3

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23 changes: 15 additions & 8 deletions aes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,10 @@ ECB-AES128
2b7e151628aed2a6abf7158809cf4f3c

resulting cipher
50fe67cc996d32b6da0937e99bafec60
d9a4dada0892239f6b8b3d7680e15674
a78819583f0308e7a6bf36b1386abf23
c6d3416d29165c6fcb8e51a227ba994e
3ad77bb40d7a3660a89ecaf32466ef97
f5d3d58503b9699de785895a96fdbaaf
43b1cd7f598ece23881b00e3ed030688
7b0c785e27e8ad3f8223207104725dd4


NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0)
Expand Down Expand Up @@ -65,7 +65,7 @@ static uint8_t* in, *out, state[4][4];
static uint8_t RoundKey[176];

// The Key input to the AES Program
static uint8_t* Key;
static const uint8_t* Key;

// 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 -
Expand Down Expand Up @@ -291,7 +291,14 @@ static void MixColumns()
}

// Multiplty is a macro used to multiply numbers in the field GF(2^8)
#define Multiply(x,y) (((y & 1) * x) ^ ((y>>1 & 1) * xtime(x)) ^ ((y>>2 & 1) * xtime(xtime(x))) ^ ((y>>3 & 1) * xtime(xtime(xtime(x)))) ^ ((y>>4 & 1) * xtime(xtime(xtime(xtime(x))))))
static uint8_t Multiply(uint8_t x, uint8_t y)
{
return (((y & 1) * x) ^
((y>>1 & 1) * xtime(x)) ^
((y>>2 & 1) * xtime(xtime(x))) ^
((y>>3 & 1) * xtime(xtime(xtime(x)))) ^
((y>>4 & 1) * xtime(xtime(xtime(xtime(x))))));
}


// MixColumns function mixes the columns of the state matrix.
Expand Down Expand Up @@ -456,7 +463,7 @@ static void InvCipher()
/* Public functions: */
/*****************************************************************************/

void AES128_ECB_encrypt(uint8_t* input, uint8_t* key, uint8_t *output)
void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t *output)
{
// Copy the Key and CipherText
Key = key;
Expand All @@ -470,7 +477,7 @@ void AES128_ECB_encrypt(uint8_t* input, uint8_t* key, uint8_t *output)
Cipher();
}

void AES128_ECB_decrypt(uint8_t* input, uint8_t* key, uint8_t *output)
void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t *output)
{
Key = key;
in = input;
Expand Down
4 changes: 2 additions & 2 deletions aes.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@

#include <stdint.h>

void AES128_ECB_encrypt(uint8_t* input, uint8_t* key, uint8_t *output);
void AES128_ECB_decrypt(uint8_t* input, uint8_t* key, uint8_t *output);
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);

#endif //_AES_H_