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Code Issues Releases Activity

avutil/aes_ctr: reintroduce the block offset state

Browse Source 
Wrongly removed in fe73b84879, it's required for
calls with a payload smaller than a full block.

Fixes issue #20474.

Signed-off-by: James Almer <jamrial@gmail.com>
This commit is contained in:
James Almer
2025-09-09 11:31:45 -03:00
parent c1dc2e2b7c
commit 335ba4a649
1 changed files with 16 additions and 1 deletions
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17
libavutil/aes_ctr.c
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@@ -34,6 +34,7 @@
typedef struct AVAESCTR {
DECLARE_ALIGNED(8, uint8_t, counter)[AES_BLOCK_SIZE];
DECLARE_ALIGNED(8, uint8_t, encrypted_counter)[AES_BLOCK_SIZE];
int block_offset;
AVAES aes;
} AVAESCTR;
@@ -46,11 +47,13 @@ void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
{
memcpy(a->counter, iv, AES_CTR_IV_SIZE);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv)
{
memcpy(a->counter, iv, sizeof(a->counter));
a->block_offset = 0;
}
const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
@@ -73,6 +76,7 @@ int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
av_aes_init(&a->aes, key, 128, 0);
memset(a->counter, 0, sizeof(a->counter));
a->block_offset = 0;
return 0;
}
@@ -92,10 +96,21 @@ void av_aes_ctr_increment_iv(struct AVAESCTR *a)
{
av_aes_ctr_increment_be64(a->counter);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
{
if (a->block_offset && count > 0) {
int left = FFMIN(count, AES_BLOCK_SIZE - a->block_offset);
for (int len = 0; len < left; len++)
dst[len] = src[len] ^ a->encrypted_counter[a->block_offset++];
a->block_offset &= AES_BLOCK_SIZE - 1;
dst += left;
src += left;
count -= left;
}
while (count >= AES_BLOCK_SIZE) {
av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
@@ -115,6 +130,6 @@ void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int
av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
for (int len = 0; len < count; len++)
dst[len] = src[len] ^ a->encrypted_counter[len];
dst[len] = src[len] ^ a->encrypted_counter[a->block_offset++];
}
}