Iterate in 16-byte chunks
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/aes.c b/library/aes.c
index f4b9739..ced8a32 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1441,36 +1441,42 @@
const unsigned char *input,
unsigned char *output)
{
- int c, i;
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
- size_t n;
- n = *nc_off;
+ size_t offset = *nc_off;
- if (n > 0x0F) {
+ if (offset > 0x0F) {
return MBEDTLS_ERR_AES_BAD_INPUT_DATA;
}
- while (length--) {
- if (n == 0) {
+ for (size_t i = 0; i < length;) {
+ size_t n = 16;
+ if (offset == 0) {
ret = mbedtls_aes_crypt_ecb(ctx, MBEDTLS_AES_ENCRYPT, nonce_counter, stream_block);
if (ret != 0) {
goto exit;
}
-
- for (i = 16; i > 0; i--) {
- if (++nonce_counter[i - 1] != 0) {
+ for (int j = 16; j > 0; j--) {
+ if (++nonce_counter[j - 1] != 0) {
break;
}
}
+ } else {
+ n -= offset;
}
- c = *input++;
- *output++ = (unsigned char) (c ^ stream_block[n]);
- n = (n + 1) & 0x0F;
+ if (n > (length - i)) {
+ n = (length - i);
+ }
+ mbedtls_xor(&output[i], &input[i], &stream_block[offset], n);
+ // offset might be non-zero for the last block, but in that case, we don't use it again
+ offset = 0;
+ i += n;
}
- *nc_off = n;
+ // capture offset for future resumption
+ *nc_off = (*nc_off + length) % 16;
+
ret = 0;
exit: