mirror of https://github.com/kokke/tiny-AES-c
Update aes.c
Kindly accepting corrections and additions from jcallan :)
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kokke
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aes.c
78
aes.c
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@ -18,10 +18,10 @@ ECB-AES128
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2b7e151628aed2a6abf7158809cf4f3c
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resulting cipher
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50fe67cc996d32b6da0937e99bafec60
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d9a4dada0892239f6b8b3d7680e15674
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a78819583f0308e7a6bf36b1386abf23
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c6d3416d29165c6fcb8e51a227ba994e
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3ad77bb40d7a3660a89ecaf32466ef97
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f5d3d58503b9699de785895a96fdbaaf
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43b1cd7f598ece23881b00e3ed030688
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7b0c785e27e8ad3f8223207104725dd4
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NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0)
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@ -29,9 +29,6 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0)
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*/
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#ifndef _AES_C_
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#define _AES_C_
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/*****************************************************************************/
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/* Includes: */
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@ -52,6 +49,10 @@ NOTE: String length must be evenly divisible by 16byte (str_len % 16 == 0)
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// The number of rounds in AES Cipher.
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#define Nr 10
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// jcallan@github points out that declaring Multiply as a function
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// reduces code size considerably with the Keil ARM compiler.
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// See this link for more information: https://github.com/kokke/tiny-AES128-C/pull/3
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#define MULTIPLY_AS_A_FUNCTION 0
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/*****************************************************************************/
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/* Private variables: */
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@ -143,9 +144,8 @@ static uint8_t getSBoxInvert(uint8_t num)
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return rsbox[num];
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}
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// This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states.
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static void KeyExpansion()
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static void KeyExpansion(void)
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{
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uint32_t i, j, k;
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uint8_t tempa[4]; // Used for the column/row operations
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@ -212,10 +212,10 @@ static void KeyExpansion()
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// This function adds the round key to state.
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// The round key is added to the state by an XOR function.
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static void AddRoundKey(uint8_t round)
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static void AddRoundKey(uint8_t round)
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{
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uint8_t i,j;
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for(i=0;i<4;i++)
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for(i=0;i<4;++i)
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{
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for(j = 0; j < 4; ++j)
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{
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@ -226,7 +226,7 @@ static void AddRoundKey(uint8_t round)
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// The SubBytes Function Substitutes the values in the
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// state matrix with values in an S-box.
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static void SubBytes()
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static void SubBytes(void)
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{
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uint8_t i, j;
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for(i = 0; i < 4; ++i)
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@ -241,7 +241,7 @@ static void SubBytes()
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// The ShiftRows() function shifts the rows in the state to the left.
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// Each row is shifted with different offset.
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// Offset = Row number. So the first row is not shifted.
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static void ShiftRows()
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static void ShiftRows(void)
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{
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uint8_t temp;
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@ -275,7 +275,7 @@ static uint8_t xtime(uint8_t x)
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}
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// MixColumns function mixes the columns of the state matrix
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static void MixColumns()
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static void MixColumns(void)
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{
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uint8_t i;
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uint8_t Tmp,Tm,t;
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@ -290,18 +290,36 @@ static void MixColumns()
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}
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}
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// Multiplty is a macro used to multiply numbers in the field GF(2^8)
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#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))))))
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// Multiply is used to multiply numbers in the field GF(2^8)
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#if MULTIPLY_AS_A_FUNCTION
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static uint8_t Multiply(uint8_t x, uint8_t y)
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{
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return (((y & 1) * x) ^
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((y>>1 & 1) * xtime(x)) ^
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((y>>2 & 1) * xtime(xtime(x))) ^
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((y>>3 & 1) * xtime(xtime(xtime(x)))) ^
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((y>>4 & 1) * xtime(xtime(xtime(xtime(x))))));
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}
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#else
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#define Multiply(x, y) \
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( ((y & 1) * x) ^ \
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((y>>1 & 1) * xtime(x)) ^ \
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((y>>2 & 1) * xtime(xtime(x))) ^ \
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((y>>3 & 1) * xtime(xtime(xtime(x)))) ^ \
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((y>>4 & 1) * xtime(xtime(xtime(xtime(x)))))) \
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#endif
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// MixColumns function mixes the columns of the state matrix.
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// The method used to multiply may be difficult to understand for the inexperienced.
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// Please use the references to gain more information.
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static void InvMixColumns()
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static void InvMixColumns(void)
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{
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int i;
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uint8_t a,b,c,d;
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for(i=0;i<4;i++)
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for(i=0;i<4;++i)
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{
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a = state[0][i];
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@ -320,20 +338,19 @@ static void InvMixColumns()
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// The SubBytes Function Substitutes the values in the
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// state matrix with values in an S-box.
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static void InvSubBytes()
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static void InvSubBytes(void)
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{
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uint8_t i,j;
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for(i=0;i<4;i++)
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for(i=0;i<4;++i)
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{
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for(j=0;j<4;j++)
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for(j=0;j<4;++j)
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{
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state[i][j] = getSBoxInvert(state[i][j]);
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}
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}
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}
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static void InvShiftRows()
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static void InvShiftRows(void)
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{
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uint8_t temp;
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@ -363,7 +380,7 @@ static void InvShiftRows()
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// Cipher is the main function that encrypts the PlainText.
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static void Cipher()
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static void Cipher(void)
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{
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uint8_t i, j, round = 0;
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@ -407,14 +424,14 @@ static void Cipher()
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}
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}
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static void InvCipher()
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static void InvCipher(void)
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{
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uint8_t i,j,round=0;
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// Copy the input CipherText to state array.
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for(i=0;i<4;i++)
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for(i=0;i<4;++i)
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{
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for(j=0;j<4;j++)
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for(j=0;j<4;++j)
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{
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state[j][i] = in[i*4 + j];
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}
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@ -442,9 +459,9 @@ static void InvCipher()
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// The decryption process is over.
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// Copy the state array to output array.
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for(i=0;i<4;i++)
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for(i=0;i<4;++i)
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{
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for(j=0;j<4;j++)
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for(j=0;j<4;++j)
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{
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out[i*4+j]=state[j][i];
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}
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@ -481,6 +498,3 @@ void AES128_ECB_decrypt(uint8_t* input, uint8_t* key, uint8_t *output)
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InvCipher();
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}
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#endif //_AES_C_
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