Use PROGMEM for lookup tables on AVR platforms

Author: StarGate01

aes.c

@@ -38,6 +38,10 @@ NOTE:   String length must be evenly divisible by 16byte (str_len % 16 == 0)
 #include <string.h> // CBC mode, for memset
 #include "aes.h"
 
+#ifdef __AVR__
+#include <avr/pgmspace.h> // For PROGMEM
+#endif
+
 /*****************************************************************************/
 /* Defines:                                                                  */
 /*****************************************************************************/
@@ -76,7 +80,11 @@ typedef uint8_t state_t[4][4];
 // 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.
+#ifndef __AVR__
 static const uint8_t sbox[256] = {
+#else 
+static const uint8_t sbox[256] PROGMEM = {
+#endif
   //0     1    2      3     4    5     6     7      8    9     A      B    C     D     E     F
   0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
   0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
@@ -96,7 +104,11 @@ static const uint8_t sbox[256] = {
   0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 };
 
 #if (defined(CBC) && CBC == 1) || (defined(ECB) && ECB == 1)
+#ifndef __AVR__
 static const uint8_t rsbox[256] = {
+#else 
+static const uint8_t rsbox[256] PROGMEM = {
+#endif
   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,
@@ -117,7 +129,11 @@ static const uint8_t rsbox[256] = {
 
 // The round constant word array, Rcon[i], contains the values given by 
 // x to the power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
+#ifndef __AVR__
 static const uint8_t Rcon[11] = {
+#else 
+static const uint8_t Rcon[11] PROGMEM = {
+#endif
   0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36 };
 
 /*
@@ -140,7 +156,11 @@ static uint8_t getSBoxValue(uint8_t num)
   return sbox[num];
 }
 */
+#ifndef __AVR__
 #define getSBoxValue(num) (sbox[(num)])
+#else
+#define getSBoxValue(num) (pgm_read_byte(sbox + (num)))
+#endif
 
 // This function produces Nb(Nr+1) round keys. The round keys are used in each round to decrypt the states. 
 static void KeyExpansion(uint8_t* RoundKey, const uint8_t* Key)
@@ -194,7 +214,11 @@ static void KeyExpansion(uint8_t* RoundKey, const uint8_t* Key)
         tempa[3] = getSBoxValue(tempa[3]);
       }
 
+#ifndef __AVR__
       tempa[0] = tempa[0] ^ Rcon[i/Nk];
+#else
+      tempa[0] = tempa[0] ^ (pgm_read_byte(Rcon + (i/Nk)));
+#endif
     }
 #if defined(AES256) && (AES256 == 1)
     if (i % Nk == 4)
@@ -342,7 +366,11 @@ static uint8_t getSBoxInvert(uint8_t num)
   return rsbox[num];
 }
 */
+#ifndef __AVR__
 #define getSBoxInvert(num) (rsbox[(num)])
+#else
+#define getSBoxInvert(num) (pgm_read_byte(rsbox + (num)))
+#endif
 
 // MixColumns function mixes the columns of the state matrix.
 // The method used to multiply may be difficult to understand for the inexperienced.