1 files changed, 157 insertions, 4 deletions

diff --git a/aes.c b/aes.c
index fbdad26..000a067 100644
--- a/aes.c
+++ b/aes.c
@@ -18,10 +18,10 @@ ECB-AES128
     2b7e151628aed2a6abf7158809cf4f3c
 
   resulting cipher
-    3ad77bb40d7a3660a89ecaf32466ef97
-    f5d3d58503b9699de785895a96fdbaaf
-    43b1cd7f598ece23881b00e3ed030688
-    7b0c785e27e8ad3f8223207104725dd4
+    50fe67cc996d32b6da0937e99bafec60
+    d9a4dada0892239f6b8b3d7680e15674
+    a78819583f0308e7a6bf36b1386abf23
+    c6d3416d29165c6fcb8e51a227ba994e
 
 
 NOTE:   String length must be evenly divisible by 16byte (str_len % 16 == 0)
@@ -89,6 +89,25 @@ static const uint8_t sbox[256] =   {
   0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
   0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 };
 
+static const uint8_t rsbox[256] =
+{ 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb
+, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb
+, 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e
+, 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25
+, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92
+, 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84
+, 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06
+, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b
+, 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73
+, 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e
+, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b
+, 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4
+, 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f
+, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef
+, 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61
+, 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d };
+
+
 // The round constant word array, Rcon[i], contains the values given by 
 // x to th e power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
 // Note that i starts at 1, not 0).
@@ -119,6 +138,12 @@ static uint8_t getSBoxValue(uint8_t num)
   return sbox[num];
 }
 
+static uint8_t getSBoxInvert(uint8_t num)
+{
+  return rsbox[num];
+}
+
+
 // This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states. 
 static void KeyExpansion()
 {
@@ -265,6 +290,78 @@ 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))))))
+
+
+// MixColumns function mixes the columns of the state matrix.
+// The method used to multiply may be difficult to understand for the inexperienced.
+// Please use the references to gain more information.
+static void InvMixColumns()
+{
+  int i;
+  uint8_t a,b,c,d;
+  for(i=0;i<4;i++)
+  { 
+  
+    a = state[0][i];
+    b = state[1][i];
+    c = state[2][i];
+    d = state[3][i];
+
+    
+    state[0][i] = Multiply(a, 0x0e) ^ Multiply(b, 0x0b) ^ Multiply(c, 0x0d) ^ Multiply(d, 0x09);
+    state[1][i] = Multiply(a, 0x09) ^ Multiply(b, 0x0e) ^ Multiply(c, 0x0b) ^ Multiply(d, 0x0d);
+    state[2][i] = Multiply(a, 0x0d) ^ Multiply(b, 0x09) ^ Multiply(c, 0x0e) ^ Multiply(d, 0x0b);
+    state[3][i] = Multiply(a, 0x0b) ^ Multiply(b, 0x0d) ^ Multiply(c, 0x09) ^ Multiply(d, 0x0e);
+  }
+}
+
+
+// The SubBytes Function Substitutes the values in the
+// state matrix with values in an S-box.
+static void InvSubBytes()
+{
+  uint8_t i,j;
+  for(i=0;i<4;i++)
+  {
+    for(j=0;j<4;j++)
+    {
+      state[i][j] = getSBoxInvert(state[i][j]);
+    }
+  }
+}
+
+
+static void InvShiftRows()
+{
+  uint8_t temp;
+
+  // Rotate first row 1 columns to right  
+  temp=state[1][3];
+  state[1][3]=state[1][2];
+  state[1][2]=state[1][1];
+  state[1][1]=state[1][0];
+  state[1][0]=temp;
+
+  // Rotate second row 2 columns to right 
+  temp=state[2][0];
+  state[2][0]=state[2][2];
+  state[2][2]=temp;
+
+  temp=state[2][1];
+  state[2][1]=state[2][3];
+  state[2][3]=temp;
+
+  // Rotate third row 3 columns to right
+  temp=state[3][0];
+  state[3][0]=state[3][1];
+  state[3][1]=state[3][2];
+  state[3][2]=state[3][3];
+  state[3][3]=temp;
+}
+
+
 // Cipher is the main function that encrypts the PlainText.
 static void Cipher()
 {
@@ -310,6 +407,50 @@ static void Cipher()
   }
 }
 
+static void InvCipher()
+{
+  uint8_t i,j,round=0;
+
+  //Copy the input CipherText to state array.
+  for(i=0;i<4;i++)
+  {
+    for(j=0;j<4;j++)
+    {
+      state[j][i] = in[i*4 + j];
+    }
+  }
+
+  // Add the First round key to the state before starting the rounds.
+  AddRoundKey(Nr); 
+
+  // There will be Nr rounds.
+  // The first Nr-1 rounds are identical.
+  // These Nr-1 rounds are executed in the loop below.
+  for(round=Nr-1;round>0;round--)
+  {
+    InvShiftRows();
+    InvSubBytes();
+    AddRoundKey(round);
+    InvMixColumns();
+  }
+  
+  // The last round is given below.
+  // The MixColumns function is not here in the last round.
+  InvShiftRows();
+  InvSubBytes();
+  AddRoundKey(0);
+
+  // The decryption process is over.
+  // Copy the state array to output array.
+  for(i=0;i<4;i++)
+  {
+    for(j=0;j<4;j++)
+    {
+      out[i*4+j]=state[j][i];
+    }
+  }
+}
+
 
 /*****************************************************************************/
 /* Public functions:                                                         */
@@ -329,5 +470,17 @@ 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)
+{
+  Key = key;
+  in = input;
+  out = output;
+
+  KeyExpansion();
+
+  InvCipher();
+}
 
 #endif //_AES_C_
+
+