Commits on Jul 14, 2022

1. Resolve aes cmac token generation bug if input data is chunked …

   If the tc_cmac_update() function is called and fills the internal leftover cache completely, the following tc_cmac_final() call will produce a wrong token.
   
   If the tc_cmac_update() is called with a data length which fills up the internal leftover cache completely, the leftover data will be processed instantly and is left empty. This is not the right behavior, because tc_cmac_final() requires that the last block is still in the leftover cache and not processed, because it need special treatment.
   
   Bug reproduction code:
   
   ~~~c
   #include "tinycrypt/cmac_mode.h"
   #include "tinycrypt/aes.h"
   #include "tinycrypt/utils.h"
   #include "tinycrypt/constants.h"
   #include <stdlib.h>
   #include <stdio.h>
   
   #define ASSERT_TRUE(cond) if (!(cond)) {printf("Test failed!\n"); return -1;}
   
   const uint8_t testData[16] =
   {
       0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10
   };
   
   const uint8_t key[TC_AES_KEY_SIZE] =
   {
       0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0x12
   };
   
   uint8_t token1[TC_AES_BLOCK_SIZE];
   uint8_t token2[TC_AES_BLOCK_SIZE];
   
   int main()
   {
       {
           struct tc_cmac_struct ctx;
           struct tc_aes_key_sched_struct sched;
           ASSERT_TRUE(tc_cmac_init(&ctx) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_setup(&ctx, key, &sched) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_update(&ctx, testData, sizeof(testData)) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_final(token1, &ctx) == TC_CRYPTO_SUCCESS);
       }
   
       {
           const size_t splitOffset = 8;
           struct tc_cmac_struct ctx;
           struct tc_aes_key_sched_struct sched;
           ASSERT_TRUE(tc_cmac_init(&ctx) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_setup(&ctx, key, &sched) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_update(&ctx, testData, splitOffset) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_update(&ctx, &testData[splitOffset] , TC_AES_BLOCK_SIZE - splitOffset) == TC_CRYPTO_SUCCESS);
           ASSERT_TRUE(tc_cmac_final(token2, &ctx) == TC_CRYPTO_SUCCESS);
       }
   
       ASSERT_TRUE(memcmp(token1, token2, TC_AES_BLOCK_SIZE) == 0); //will fail, tokens do not match
   
       printf("Test ok!\n");
   }
   ~~~

   

   KonsKr committed Jul 14, 2022
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