more consistent signature mismatch error on mac (#167)

source/darwin/securityframework_rsa.c

@@ -56,9 +56,34 @@ static int s_reinterpret_sec_error_as_crt(CFErrorRef error, const char *function
     CFIndex error_code = CFErrorGetCode(error);
     CFStringRef error_message = CFErrorCopyDescription(error); /* This function never returns NULL */
 
-    const char *error_cstr = CFStringGetCStringPtr(error_message, kCFStringEncodingASCII);
+    /*
+     * Note: CFStringGetCStringPtr returns NULL quite often.
+     * Refer to writeup at the start of CFString.h as to why.
+     * To reliably get an error message we need to use the following function
+     * that will copy error string into our buffer.
+     */
+    const char *error_cstr = NULL;
+    char buffer[128];
+    if (CFStringGetCString(error_message, buffer, 128, kCFStringEncodingUTF8)) {
+        error_cstr = buffer;
+    }
+
     int crt_error = AWS_ERROR_CAL_CRYPTO_OPERATION_FAILED;
 
+    /*
+     * Mac seems throws errSecVerifyFailed for any signature verification
+     * failures (based on testing and not review of their code).
+     * Which makes it impossible to distinguish between signature validation
+     * failure and api call failure.
+     * So let errSecVerifyFailed as signature validation failure, rather than a
+     * more generic Crypto Failure as it seems more intuitive to caller that
+     * signature cannot be verified, rather than something wrong with crypto (and
+     * in most cases crypto is working correctly, but returning non-specific error).
+     */
+    if (error_code == errSecVerifyFailed) {
+        crt_error = AWS_ERROR_CAL_SIGNATURE_VALIDATION_FAILED;
+    }
+
     AWS_LOGF_ERROR(
         AWS_LS_CAL_RSA,
         "%s() failed. CFError:%ld(%s) aws_error:%s",

tests/CMakeLists.txt

@@ -85,6 +85,7 @@ add_test_case(rsa_verify_signing_pss_sha256)
 add_test_case(rsa_decrypt_pkcs1)
 add_test_case(rsa_decrypt_oaep256)
 add_test_case(rsa_decrypt_oaep512)
+add_test_case(rsa_signing_mismatch_pkcs1_sha256)
 
 add_test_case(aes_cbc_NIST_CBCGFSbox256_case_1)
 add_test_case(aes_cbc_NIST_CBCVarKey256_case_254)

tests/rsa_test.c

@@ -689,3 +689,53 @@ static int s_rsa_public_pkcs1_der_parsing(struct aws_allocator *allocator, void
     return AWS_OP_SUCCESS;
 }
 AWS_TEST_CASE(rsa_public_pkcs1_der_parsing, s_rsa_public_pkcs1_der_parsing);
+
+static int s_rsa_signing_mismatch_pkcs1_sha256(struct aws_allocator *allocator, void *ctx) {
+    (void)ctx;
+    struct aws_byte_cursor message = aws_byte_cursor_from_c_str(TEST_ENCRYPTION_STRING);
+
+    aws_cal_library_init(allocator);
+
+    struct aws_byte_buf public_key_buf;
+    ASSERT_SUCCESS(s_byte_buf_decoded_from_base64_cur(
+        allocator, aws_byte_cursor_from_c_str(TEST_PKCS1_RSA_PRIVATE_KEY_1024), &public_key_buf));
+    struct aws_rsa_key_pair *key_pair_private =
+        aws_rsa_key_pair_new_from_private_key_pkcs1(allocator, aws_byte_cursor_from_buf(&public_key_buf));
+    ASSERT_NOT_NULL(key_pair_private);
+
+    uint8_t hash[AWS_SHA256_LEN];
+    AWS_ZERO_ARRAY(hash);
+    struct aws_byte_buf hash_value = aws_byte_buf_from_empty_array(hash, sizeof(hash));
+    aws_sha256_compute(allocator, &message, &hash_value, 0);
+    struct aws_byte_cursor hash_cur = aws_byte_cursor_from_buf(&hash_value);
+
+    struct aws_byte_buf signature_buf;
+    ASSERT_SUCCESS(aws_byte_buf_init(&signature_buf, allocator, aws_rsa_key_pair_signature_length(key_pair_private)));
+    ASSERT_SUCCESS(aws_rsa_key_pair_sign_message(
+        key_pair_private, AWS_CAL_RSA_SIGNATURE_PKCS1_5_SHA256, hash_cur, &signature_buf));
+    struct aws_byte_cursor signature_cur = aws_byte_cursor_from_buf(&signature_buf);
+
+    hash[5] += 59; /* modify digest to force signature mismatch */
+
+    ASSERT_ERROR(
+        AWS_ERROR_CAL_SIGNATURE_VALIDATION_FAILED,
+        aws_rsa_key_pair_verify_signature(
+            key_pair_private, AWS_CAL_RSA_SIGNATURE_PKCS1_5_SHA256, hash_cur, signature_cur));
+
+    hash[5] -= 59; /* undo digest modification and corrupt signature */
+    signature_buf.buffer[5] += 59;
+    ASSERT_ERROR(
+        AWS_ERROR_CAL_SIGNATURE_VALIDATION_FAILED,
+        aws_rsa_key_pair_verify_signature(
+            key_pair_private, AWS_CAL_RSA_SIGNATURE_PKCS1_5_SHA256, hash_cur, signature_cur));
+
+    aws_byte_buf_clean_up(&hash_value);
+    aws_byte_buf_clean_up(&signature_buf);
+    aws_byte_buf_clean_up(&public_key_buf);
+    aws_rsa_key_pair_release(key_pair_private);
+
+    aws_cal_library_clean_up();
+
+    return AWS_OP_SUCCESS;
+}
+AWS_TEST_CASE(rsa_signing_mismatch_pkcs1_sha256, s_rsa_signing_mismatch_pkcs1_sha256);