From 89017afdb2ab9ab7209def7750b793d97a4da3a9 Mon Sep 17 00:00:00 2001
From: Denis Kenzior <denkenz@gmail.com>
Date: Wed, 17 Apr 2019 18:59:27 -0500
Subject: [PATCH] crypto: Skip aes-ctr decryption for in_len = 16

If the input length is 16 bytes, this means aes_siv_decrypt should
only be verifying the 16 byte SIV and not decrypting any data. If
this is the case, we can skip over the whole AES-CTR portion of
AES-SIV and only verify the SIV.
---
 src/crypto.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/crypto.c b/src/crypto.c
index ecf35f7d..85de78f3 100644
--- a/src/crypto.c
+++ b/src/crypto.c
@@ -365,11 +365,17 @@ bool aes_siv_decrypt(const uint8_t *key, size_t key_len, const uint8_t *in,
 	uint8_t iv[16];
 	uint8_t v[16];
 
+	if (in_len < 16)
+		return false;
+
 	memcpy(iov, ad, sizeof(iov) * num_ad);
 	iov[num_ad].iov_base = (void *)out;
 	iov[num_ad].iov_len = in_len - 16;
 	num_ad++;
 
+	if (in_len == 16)
+		goto check_cmac;
+
 	memcpy(iv, in, 16);
 
 	iv[8] &= 0x7f;
@@ -387,6 +393,7 @@ bool aes_siv_decrypt(const uint8_t *key, size_t key_len, const uint8_t *in,
 
 	l_cipher_free(ctr);
 
+check_cmac:
 	cmac = l_checksum_new_cmac_aes(key, key_len / 2);
 	if (!cmac)
 		return false;