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libavformat/mov: add support for 'cens', 'cbc1' and 'cbcs' encryption schemes specified in Common Encryption (CENC) standard

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correct implementation of 'cenc' encryption scheme to support
decryption of partial cipher blocks at the end of subsamples

https://www.iso.org/standard/68042.html

Signed-off-by: Nachiket Tarate <nachiket.programmer@gmail.com>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>
This commit is contained in:
Nachiket Tarate 2021-09-22 00:11:31 +05:30 committed by Steven Liu
parent 343c03c61c
commit ef0f5d1be6
2 changed files with 243 additions and 8 deletions
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2
libavformat/isom.h
View File

@ -237,6 +237,8 @@ typedef struct MOVStreamContext {
int has_sidx; // If there is an sidx entry for this stream.
struct {
struct AVAESCTR* aes_ctr;
struct AVAES *aes_ctx;
unsigned int frag_index_entry_base;
unsigned int per_sample_iv_size; // Either 0, 8, or 16.
AVEncryptionInfo *default_encrypted_sample;
MOVEncryptionIndex *encryption_index;

249
libavformat/mov.c
View File

@ -6598,14 +6598,13 @@ static int mov_read_dfla(MOVContext *c, AVIOContext *pb, MOVAtom atom)
return 0;
}
static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
static int cenc_scheme_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
{
int i, ret;
if (sample->scheme != MKBETAG('c','e','n','c') || sample->crypt_byte_block != 0 || sample->skip_byte_block != 0) {
av_log(c->fc, AV_LOG_ERROR, "Only the 'cenc' encryption scheme is supported\n");
return AVERROR_PATCHWELCOME;
}
int bytes_of_protected_data;
int partially_encrypted_block_size;
uint8_t *partially_encrypted_block;
uint8_t block[16];
if (!sc->cenc.aes_ctr) {
/* initialize the cipher */
@ -6628,6 +6627,8 @@ static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *s
return 0;
}
partially_encrypted_block_size = 0;
for (i = 0; i < sample->subsample_count; i++) {
if (sample->subsamples[i].bytes_of_clear_data + sample->subsamples[i].bytes_of_protected_data > size) {
av_log(c->fc, AV_LOG_ERROR, "subsample size exceeds the packet size left\n");
@ -6639,7 +6640,90 @@ static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *s
size -= sample->subsamples[i].bytes_of_clear_data;
/* decrypt the encrypted bytes */
av_aes_ctr_crypt(sc->cenc.aes_ctr, input, input, sample->subsamples[i].bytes_of_protected_data);
if (partially_encrypted_block_size) {
memcpy(block, partially_encrypted_block, partially_encrypted_block_size);
memcpy(block+partially_encrypted_block_size, input, 16-partially_encrypted_block_size);
av_aes_ctr_crypt(sc->cenc.aes_ctr, block, block, 16);
memcpy(partially_encrypted_block, block, partially_encrypted_block_size);
memcpy(input, block+partially_encrypted_block_size, 16-partially_encrypted_block_size);
input += 16-partially_encrypted_block_size;
size -= 16-partially_encrypted_block_size;
bytes_of_protected_data = sample->subsamples[i].bytes_of_protected_data - (16-partially_encrypted_block_size);
} else {
bytes_of_protected_data = sample->subsamples[i].bytes_of_protected_data;
}
if (i < sample->subsample_count-1) {
int num_of_encrypted_blocks = bytes_of_protected_data/16;
partially_encrypted_block_size = bytes_of_protected_data%16;
if (partially_encrypted_block_size)
partially_encrypted_block = input + 16*num_of_encrypted_blocks;
av_aes_ctr_crypt(sc->cenc.aes_ctr, input, input, 16*num_of_encrypted_blocks);
} else {
av_aes_ctr_crypt(sc->cenc.aes_ctr, input, input, bytes_of_protected_data);
}
input += bytes_of_protected_data;
size -= bytes_of_protected_data;
}
if (size > 0) {
av_log(c->fc, AV_LOG_ERROR, "leftover packet bytes after subsample processing\n");
return AVERROR_INVALIDDATA;
}
return 0;
}
static int cbc1_scheme_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
{
int i, ret;
int num_of_encrypted_blocks;
uint8_t iv[16];
if (!sc->cenc.aes_ctx) {
/* initialize the cipher */
sc->cenc.aes_ctx = av_aes_alloc();
if (!sc->cenc.aes_ctx) {
return AVERROR(ENOMEM);
}
ret = av_aes_init(sc->cenc.aes_ctx, c->decryption_key, 16 * 8, 1);
if (ret < 0) {
return ret;
}
}
memcpy(iv, sample->iv, 16);
/* whole-block full sample encryption */
if (!sample->subsample_count) {
/* decrypt the whole packet */
av_aes_crypt(sc->cenc.aes_ctx, input, input, size/16, iv, 1);
return 0;
}
for (i = 0; i < sample->subsample_count; i++) {
if (sample->subsamples[i].bytes_of_clear_data + sample->subsamples[i].bytes_of_protected_data > size) {
av_log(c->fc, AV_LOG_ERROR, "subsample size exceeds the packet size left\n");
return AVERROR_INVALIDDATA;
}
if (sample->subsamples[i].bytes_of_protected_data % 16) {
av_log(c->fc, AV_LOG_ERROR, "subsample BytesOfProtectedData is not a multiple of 16\n");
return AVERROR_INVALIDDATA;
}
/* skip the clear bytes */
input += sample->subsamples[i].bytes_of_clear_data;
size -= sample->subsamples[i].bytes_of_clear_data;
/* decrypt the encrypted bytes */
num_of_encrypted_blocks = sample->subsamples[i].bytes_of_protected_data/16;
if (num_of_encrypted_blocks > 0) {
av_aes_crypt(sc->cenc.aes_ctx, input, input, num_of_encrypted_blocks, iv, 1);
}
input += sample->subsamples[i].bytes_of_protected_data;
size -= sample->subsamples[i].bytes_of_protected_data;
}
@ -6652,6 +6736,153 @@ static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *s
return 0;
}
static int cens_scheme_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
{
int i, ret, rem_bytes;
uint8_t *data;
if (!sc->cenc.aes_ctr) {
/* initialize the cipher */
sc->cenc.aes_ctr = av_aes_ctr_alloc();
if (!sc->cenc.aes_ctr) {
return AVERROR(ENOMEM);
}
ret = av_aes_ctr_init(sc->cenc.aes_ctr, c->decryption_key);
if (ret < 0) {
return ret;
}
}
av_aes_ctr_set_full_iv(sc->cenc.aes_ctr, sample->iv);
/* whole-block full sample encryption */
if (!sample->subsample_count) {
/* decrypt the whole packet */
av_aes_ctr_crypt(sc->cenc.aes_ctr, input, input, size);
return 0;
} else if (!sample->crypt_byte_block && !sample->skip_byte_block) {
av_log(c->fc, AV_LOG_ERROR, "pattern encryption is not present in 'cens' scheme\n");
return AVERROR_INVALIDDATA;
}
for (i = 0; i < sample->subsample_count; i++) {
if (sample->subsamples[i].bytes_of_clear_data + sample->subsamples[i].bytes_of_protected_data > size) {
av_log(c->fc, AV_LOG_ERROR, "subsample size exceeds the packet size left\n");
return AVERROR_INVALIDDATA;
}
/* skip the clear bytes */
input += sample->subsamples[i].bytes_of_clear_data;
size -= sample->subsamples[i].bytes_of_clear_data;
/* decrypt the encrypted bytes */
data = input;
rem_bytes = sample->subsamples[i].bytes_of_protected_data;
while (rem_bytes > 0) {
if (rem_bytes < 16*sample->crypt_byte_block) {
break;
}
av_aes_ctr_crypt(sc->cenc.aes_ctr, data, data, 16*sample->crypt_byte_block);
data += 16*sample->crypt_byte_block;
rem_bytes -= 16*sample->crypt_byte_block;
data += FFMIN(16*sample->skip_byte_block, rem_bytes);
rem_bytes -= FFMIN(16*sample->skip_byte_block, rem_bytes);
}
input += sample->subsamples[i].bytes_of_protected_data;
size -= sample->subsamples[i].bytes_of_protected_data;
}
if (size > 0) {
av_log(c->fc, AV_LOG_ERROR, "leftover packet bytes after subsample processing\n");
return AVERROR_INVALIDDATA;
}
return 0;
}
static int cbcs_scheme_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
{
int i, ret, rem_bytes;
uint8_t iv[16];
uint8_t *data;
if (!sc->cenc.aes_ctx) {
/* initialize the cipher */
sc->cenc.aes_ctx = av_aes_alloc();
if (!sc->cenc.aes_ctx) {
return AVERROR(ENOMEM);
}
ret = av_aes_init(sc->cenc.aes_ctx, c->decryption_key, 16 * 8, 1);
if (ret < 0) {
return ret;
}
}
/* whole-block full sample encryption */
if (!sample->subsample_count) {
/* decrypt the whole packet */
memcpy(iv, sample->iv, 16);
av_aes_crypt(sc->cenc.aes_ctx, input, input, size/16, iv, 1);
return 0;
} else if (!sample->crypt_byte_block && !sample->skip_byte_block) {
av_log(c->fc, AV_LOG_ERROR, "pattern encryption is not present in 'cbcs' scheme\n");
return AVERROR_INVALIDDATA;
}
for (i = 0; i < sample->subsample_count; i++) {
if (sample->subsamples[i].bytes_of_clear_data + sample->subsamples[i].bytes_of_protected_data > size) {
av_log(c->fc, AV_LOG_ERROR, "subsample size exceeds the packet size left\n");
return AVERROR_INVALIDDATA;
}
/* skip the clear bytes */
input += sample->subsamples[i].bytes_of_clear_data;
size -= sample->subsamples[i].bytes_of_clear_data;
/* decrypt the encrypted bytes */
memcpy(iv, sample->iv, 16);
data = input;
rem_bytes = sample->subsamples[i].bytes_of_protected_data;
while (rem_bytes > 0) {
if (rem_bytes < 16*sample->crypt_byte_block) {
break;
}
av_aes_crypt(sc->cenc.aes_ctx, data, data, sample->crypt_byte_block, iv, 1);
data += 16*sample->crypt_byte_block;
rem_bytes -= 16*sample->crypt_byte_block;
data += FFMIN(16*sample->skip_byte_block, rem_bytes);
rem_bytes -= FFMIN(16*sample->skip_byte_block, rem_bytes);
}
input += sample->subsamples[i].bytes_of_protected_data;
size -= sample->subsamples[i].bytes_of_protected_data;
}
if (size > 0) {
av_log(c->fc, AV_LOG_ERROR, "leftover packet bytes after subsample processing\n");
return AVERROR_INVALIDDATA;
}
return 0;
}
static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *sample, uint8_t *input, int size)
{
if (sample->scheme == MKBETAG('c','e','n','c') && !sample->crypt_byte_block && !sample->skip_byte_block) {
return cenc_scheme_decrypt(c, sc, sample, input, size);
} else if (sample->scheme == MKBETAG('c','b','c','1') && !sample->crypt_byte_block && !sample->skip_byte_block) {
return cbc1_scheme_decrypt(c, sc, sample, input, size);
} else if (sample->scheme == MKBETAG('c','e','n','s')) {
return cens_scheme_decrypt(c, sc, sample, input, size);
} else if (sample->scheme == MKBETAG('c','b','c','s')) {
return cbcs_scheme_decrypt(c, sc, sample, input, size);
} else {
av_log(c->fc, AV_LOG_ERROR, "invalid encryption scheme\n");
return AVERROR_INVALIDDATA;
}
}
static int cenc_filter(MOVContext *mov, AVStream* st, MOVStreamContext *sc, AVPacket *pkt, int current_index)
{
MOVFragmentStreamInfo *frag_stream_info;
@ -6666,7 +6897,9 @@ static int cenc_filter(MOVContext *mov, AVStream* st, MOVStreamContext *sc, AVPa
// Note this only supports encryption info in the first sample descriptor.
if (mov->fragment.stsd_id == 1) {
if (frag_stream_info->encryption_index) {
encrypted_index = current_index - frag_stream_info->index_entry;
if (!current_index && frag_stream_info->index_entry)
sc->cenc.frag_index_entry_base = frag_stream_info->index_entry;
encrypted_index = current_index - (frag_stream_info->index_entry - sc->cenc.frag_index_entry_base);
encryption_index = frag_stream_info->encryption_index;
} else {
encryption_index = sc->cenc.encryption_index;