AES context copy test: clean up

Don't use hexcmp to compare binary data. Improve readability.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_aes.function b/tests/suites/test_suite_aes.function
index d95503a..332b9a7 100644
--- a/tests/suites/test_suite_aes.function
+++ b/tests/suites/test_suite_aes.function
@@ -468,32 +468,38 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void aes_ecb_copy_context(data_t *key_str, data_t *src_str)
+void aes_ecb_copy_context(data_t *key, data_t *src)
 {
     unsigned char output1[16], output2[16], plain[16];
     mbedtls_aes_context ctx1, ctx2, ctx3;
 
+    TEST_EQUAL(src->len, 16);
+
     // Set key and encrypt with original context
     mbedtls_aes_init(&ctx1);
-    TEST_ASSERT(mbedtls_aes_setkey_enc(&ctx1, key_str->x,
-                                       key_str->len * 8) == 0);
+    TEST_ASSERT(mbedtls_aes_setkey_enc(&ctx1, key->x,
+                                       key->len * 8) == 0);
     TEST_ASSERT(mbedtls_aes_crypt_ecb(&ctx1, MBEDTLS_AES_ENCRYPT,
-                                      src_str->x, output1) == 0);
-
+                                      src->x, output1) == 0);
     ctx2 = ctx1;
-    TEST_ASSERT(mbedtls_aes_setkey_dec(&ctx1, key_str->x,
-                                       key_str->len * 8) == 0);
+
+    // Set key for decryption with original context
+    TEST_ASSERT(mbedtls_aes_setkey_dec(&ctx1, key->x,
+                                       key->len * 8) == 0);
     ctx3 = ctx1;
+
+    // Wipe the original context to make sure nothing from it is used
     memset(&ctx1, 0, sizeof(ctx1));
 
-    // Encrypt and decrypt with copied context
+    // Encrypt with copied context
     TEST_ASSERT(mbedtls_aes_crypt_ecb(&ctx2, MBEDTLS_AES_ENCRYPT,
-                                      src_str->x, output2) == 0);
+                                      src->x, output2) == 0);
+    ASSERT_COMPARE(output1, 16, output2, 16);
+
+    // Decrypt with copied context
     TEST_ASSERT(mbedtls_aes_crypt_ecb(&ctx3, MBEDTLS_AES_DECRYPT,
                                       output1, plain) == 0);
-
-    TEST_ASSERT(mbedtls_test_hexcmp(output1, output2, 16, 16) == 0);
-    TEST_ASSERT(mbedtls_test_hexcmp(src_str->x, plain, src_str->len, 16) == 0);
+    ASSERT_COMPARE(src->x, 16, plain, 16);
 }
 /* END_CASE */