[FFmpeg-devel] [PATCH v3] avformat/hlsenc: reimplement randomize of hls use av_get_random_seed

Hendrik Leppkes h.leppkes at gmail.com
Mon Jun 4 13:43:41 EEST 2018


On Mon, Jun 4, 2018 at 12:16 PM, Thomas Volkert <silvo at gmx.net> wrote:
>
> On 04.06.2018 04:55, Steven Liu wrote:
>> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
>> ---
>>  configure            |  1 -
>>  libavformat/hlsenc.c | 27 ++++++++++++---------------
>>  2 files changed, 12 insertions(+), 16 deletions(-)
>>
>> diff --git a/configure b/configure
>> index 22eeca22a5..a3d0f5837a 100755
>> --- a/configure
>> +++ b/configure
>> @@ -3127,7 +3127,6 @@ fifo_muxer_deps="threads"
>>  flac_demuxer_select="flac_parser"
>>  hds_muxer_select="flv_muxer"
>>  hls_muxer_select="mpegts_muxer"
>> -hls_muxer_suggest="gcrypt openssl"
>>  image2_alias_pix_demuxer_select="image2_demuxer"
>>  image2_brender_pix_demuxer_select="image2_demuxer"
>>  ipod_muxer_select="mov_muxer"
>> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
>> index 2268f898b0..c04c561586 100644
>> --- a/libavformat/hlsenc.c
>> +++ b/libavformat/hlsenc.c
>> @@ -27,12 +27,6 @@
>>  #include <unistd.h>
>>  #endif
>>
>> -#if CONFIG_GCRYPT
>> -#include <gcrypt.h>
>> -#elif CONFIG_OPENSSL
>> -#include <openssl/rand.h>
>> -#endif
>> -
>>  #include "libavutil/avassert.h"
>>  #include "libavutil/mathematics.h"
>>  #include "libavutil/parseutils.h"
>> @@ -569,18 +563,21 @@ fail:
>>      return ret;
>>  }
>>
>> +
>>  static int randomize(uint8_t *buf, int len)
>>  {
>> -#if CONFIG_GCRYPT
>> -    gcry_randomize(buf, len, GCRY_VERY_STRONG_RANDOM);
>> +    uint32_t tmp_number[4];
>> +    int i = 0;
>> +
>> +    if (len != 16)
>> +        return AVERROR(EINVAL);
>> +
>> +    for (i = 0; i < 4; i++)
>> +        tmp_number[i] = av_get_random_seed();
>> +
>> +    memcpy(buf, tmp_number, len);
>> +
>>      return 0;
>> -#elif CONFIG_OPENSSL
>> -    if (RAND_bytes(buf, len))
>> -        return 0;
>> -#else
>> -    return AVERROR(ENOSYS);
>> -#endif
>> -    return AVERROR(EINVAL);
>>  }
>>
>>  static int do_encrypt(AVFormatContext *s, VariantStream *vs)
>
> Does av_get_random_seed() provide the same random quality level as
> gcry_randomize() / RAND_bytes() / mbedtls_havege_random() ?
>

I can't really comment on quality, but av_get_random_seed does not use
any cryptographic randomness sources - unless you're on Windows.
On Linux it'll read /dev/urandom or /dev/random or make up its own
seed based on time as a hash, depending on whats available.

If  av_get_random_seed is supposed to be used cryptographically, it
should probably be expanded to use crypto APIs - although it being in
avutil might make that annoying linking-wise.

- Hendrik


More information about the ffmpeg-devel mailing list