Review corrections

-Guard additional static variables with AES_ONLY_ENCRYPT
-Update config.h description about memory savings
-Update test: fix typo in all.sh and adjust compiler flags

include/mbedtls/config.h

@@ -622,7 +622,10 @@
  *
  * Uncommenting this macro removes support for AES decryption.
  *
- * Tradeoff: Uncommenting this macro reduces ROM footprint by ~2.5 kB.
+ * Tradeoff: Uncommenting this macro reduces the footprint. For
+ * example, when both MBEDTLS_AES_ROM_TABLES and
+ * MBEDTLS_AES_FEWER_TABLES are enabled, enabling this macro
+ * further reduces the ROM footprint by ~2.5kB.
  *
  * Module:  library/aes.c
  *

library/aes.c

@@ -337,7 +337,6 @@ static const unsigned char RSb[256] =
 #define V(a,b,c,d) 0x##a##b##c##d
 static const uint32_t RT0[256] = { RT };
 #undef V
-#endif /* !MBEDTLS_AES_ONLY_ENCRYPT */
 
 #if !defined(MBEDTLS_AES_FEWER_TABLES)
 
@@ -354,6 +353,7 @@ static const uint32_t RT3[256] = { RT };
 #undef V
 
 #endif /* !MBEDTLS_AES_FEWER_TABLES */
+#endif /* !MBEDTLS_AES_ONLY_ENCRYPT */
 
 #undef RT
 
@@ -383,6 +383,7 @@ static uint32_t FT3[256];
 /*
  * Reverse S-box & tables
  */
+#if !defined(MBEDTLS_AES_ONLY_ENCRYPT)
 static unsigned char RSb[256];
 static uint32_t RT0[256];
 #if !defined(MBEDTLS_AES_FEWER_TABLES)
@@ -390,6 +391,7 @@ static uint32_t RT1[256];
 static uint32_t RT2[256];
 static uint32_t RT3[256];
 #endif /* !MBEDTLS_AES_FEWER_TABLES */
+#endif /* !MBEDTLS_AES_ONLY_ENCRYPT */
 
 /*
  * Round constants
@@ -434,7 +436,9 @@ static void aes_gen_tables( void )
      * generate the forward and reverse S-boxes
      */
     FSb[0x00] = 0x63;
+#if !defined(MBEDTLS_AES_ONLY_ENCRYPT)
     RSb[0x63] = 0x00;
+#endif
 
     for( i = 1; i < 256; i++ )
     {
@@ -447,7 +451,9 @@ static void aes_gen_tables( void )
         x ^= y ^ 0x63;
 
         FSb[i] = (unsigned char) x;
+#if !defined(MBEDTLS_AES_ONLY_ENCRYPT)
         RSb[x] = (unsigned char) i;
+#endif
     }
 
     /*
@@ -470,6 +476,7 @@ static void aes_gen_tables( void )
         FT3[i] = ROTL8( FT2[i] );
 #endif /* !MBEDTLS_AES_FEWER_TABLES */
 
+#if !defined(MBEDTLS_AES_ONLY_ENCRYPT)
         x = RSb[i];
 
         RT0[i] = ( (uint32_t) MUL( 0x0E, x )       ) ^
@@ -482,6 +489,7 @@ static void aes_gen_tables( void )
         RT2[i] = ROTL8( RT1[i] );
         RT3[i] = ROTL8( RT2[i] );
 #endif /* !MBEDTLS_AES_FEWER_TABLES */
+#endif /* !MBEDTLS_AES_ONLY_ENCRYPT */
     }
 }
 

tests/scripts/all.sh

@@ -1278,9 +1278,9 @@ component_test_aes_only_128_bit_keys () {
 component_test_aes_only_encrypt () {
     msg "build: default config with MBEDTLS_AES_ONLY_ENCRYPT enabled"
     scripts/config.pl set MBEDTLS_AES_ONLY_ENCRYPT
-    make CC=gcc CFLAGS='-Werror -Wall -Wextra'
+    make CC=gcc CFLAGS='-Werror -O1'
 
-    msg "test: AES_ONLY_128_BIT_KEY_LENGTH"
+    msg "test: AES_ONLY_ENCRYPT"
     make test
 }