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.program...@gmail.com> --- libavformat/isom.h | 2 + libavformat/mov.c | 246 +++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 242 insertions(+), 6 deletions(-) diff --git a/libavformat/isom.h b/libavformat/isom.h index ac1b3f3d56..705813844f 100644 --- a/libavformat/isom.h +++ b/libavformat/isom.h @@ -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; diff --git a/libavformat/mov.c b/libavformat/mov.c index e95d3d2a90..4c55741293 100644 --- a/libavformat/mov.c +++ b/libavformat/mov.c @@ -6578,15 +6578,150 @@ 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; + int bytes_of_protected_data; + int partially_encrypted_block_size; + uint8_t *partially_encrypted_block; + uint8_t block[16]; - 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; + 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); + + if (!sample->subsample_count) { + /* decrypt the whole packet */ + av_aes_ctr_crypt(sc->cenc.aes_ctr, input, input, size); + 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"); + 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 */ + + if (partially_encrypted_block_size != 0) + { + 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 != 0) + 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 != 0) { + 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; + } + + if (size > 0) { + av_log(c->fc, AV_LOG_ERROR, "leftover packet bytes after subsample processing\n"); + return AVERROR_INVALIDDATA; + } + + 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(); @@ -6602,10 +6737,14 @@ static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *s 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 == 0 && sample->skip_byte_block == 0) { + 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++) { @@ -6619,7 +6758,18 @@ 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); + 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; } @@ -6632,6 +6782,88 @@ static int cenc_decrypt(MOVContext *c, MOVStreamContext *sc, AVEncryptionInfo *s 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 == 0 && sample->skip_byte_block == 0) { + 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 == 0 && sample->skip_byte_block == 0) { + return cenc_scheme_decrypt(c, sc, sample, input, size); + } else if (sample->scheme == MKBETAG('c','b','c','1') && sample->crypt_byte_block == 0 && sample->skip_byte_block == 0) { + 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; @@ -6646,7 +6878,9 @@ 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 == 0 && frag_stream_info->index_entry > 0) + 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; -- 2.17.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
