Merge pull request #10406 from jcarrano/aes-t-table

sys/crypto: optimize AES footprint (resurrected)

makefiles/pseudomodules.inc.mk

@@ -127,4 +127,9 @@ PSEUDOMODULES += skald_eddystone
 # define optimized read function of DS18 driver as a pseudo module
 PSEUDOMODULES += ds18_optimized
 
+# By using this pseudomodule, T tables will be precalculated.
+PSEUDOMODULES += crypto_aes_precalculated
+# This pseudomodule causes a loop in AES to be unrolled (more flash, less CPU)
+PSEUDOMODULES += crypto_aes_unroll
+
 # Packages may also add modules to PSEUDOMODULES in their `Makefile.include`.

sys/crypto/doc.txt

@@ -47,6 +47,13 @@
  *
  * @endcode
  *
+ * Some aspects of the AES implementation can be fine tuned by pseudo-modules:
+ *  * crypto_aes_precalculated: Use pre-calculated T-tables. This improved
+ *       speed at the expense of increased program size. The default is to
+ *       calculate most tables on the fly.
+ *  * crypto_aes_unroll: enable manually-unrolled loops. The default is to not
+ *       have them unrolled.
+ *
  * If you need to encrypt data of arbitrary size take a look at the different
  * operation modes like: CBC, CTR or CCM.
  *

sys/include/crypto/aes.h

@@ -37,9 +37,6 @@ typedef uint32_t u32;
 typedef uint16_t u16;
 typedef uint8_t u8;
 
-
-/* This controls loop-unrolling in aes_core.c */
-#undef FULL_UNROLL
 # define GETU32(pt) (((u32)(pt)[0] << 24) ^ ((u32)(pt)[1] << 16) ^ \
                      ((u32)(pt)[2] <<  8) ^ ((u32)(pt)[3]))
 # define PUTU32(ct, st) { (ct)[0] = (u8)((st) >> 24); \