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avformat/aadec: Simplify deriving file key

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Don't use different src and dst in av_tea_crypt(); use in-place
modifications instead. Also let av_tea_crypt() encrypt all three
blocks in one call.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2021-12-05 22:47:27 +01:00
parent c9b3099210
commit d27b97b043
1 changed files with 7 additions and 15 deletions
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22
libavformat/aadec.c
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@ -71,10 +71,10 @@ static int get_second_size(char *codec_name)
static int aa_read_header(AVFormatContext *s)
{
int i, j, idx, largest_idx = -1;
int i, idx, largest_idx = -1;
uint32_t toc_size, npairs, header_seed = 0, start;
char codec_name[64] = {0};
uint8_t output[24], dst[8], src[8];
uint8_t buf[24];
int64_t largest_size = -1, current_size = -1, chapter_pos;
struct toc_entry {
uint32_t offset;
@ -156,19 +156,11 @@ static int aa_read_header(AVFormatContext *s)
if (!c->tea_ctx)
return AVERROR(ENOMEM);
av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);
output[0] = output[1] = 0; // purely for padding purposes
memcpy(output + 2, header_key, 16);
idx = 0;
for (i = 0; i < 3; i++) { // TEA CBC with weird mixed endianness
AV_WB32(src, header_seed);
AV_WB32(src + 4, header_seed + 1);
header_seed += 2;
av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 0); // TEA ECB encrypt
for (j = 0; j < TEA_BLOCK_SIZE && idx < 18; j+=1, idx+=1) {
output[idx] = output[idx] ^ dst[j];
}
}
memcpy(c->file_key, output + 2, 16); // skip first 2 bytes of output
for (int i = 0; i < 6; i++)
AV_WB32(buf + 4 * i, header_seed + i);
av_tea_crypt(c->tea_ctx, buf, buf, 3, NULL, 0);
AV_WN64(c->file_key, AV_RN64(buf + 2) ^ AV_RN64(header_key));
AV_WN64(c->file_key + 8, AV_RN64(buf + 10) ^ AV_RN64(header_key + 8));
av_log(s, AV_LOG_DEBUG, "File key is ");
for (i = 0; i < 16; i++)
av_log(s, AV_LOG_DEBUG, "%02x", c->file_key[i]);