[Freeswitch-users] Bug in libs/srtp when OpenSSL is used to provide AES-256?

[Richard Chan]

RFC-6188 violation when FreeSWITCH is compiled with libs/srtp to use
OpenSSL?

The cipher_id_type_t is set to AES_256_ICM, (if OpenSSL is NOT used then
the cipher_id_type_t is set to AES_ICM).

This means that in srtp.c: srtp_protect_rtcp() and srtp_unprotect_rtcp()
the wrong code path will be chosen for the ICM nonce and keystream will be
reused on consecutive RTCP packets.

srtp_protect_rtcp() also srtp_unprotect_rtcp():
  /*
   * if we're using rindael counter mode, set nonce and seq
   */
  if (stream->rtcp_cipher->type->id == AES_ICM) {
    v128_t iv;

    iv.v32[0] = 0;


As a result FS 1.6.15 is generating invalid SRTCP packets when AES-256 is
being used (and libs/srtp is compiled to use OpenSSL).

Note: RTP explicitly checks for AES_ICM and AES_256_ICM so it is not
affected. It will be affected if AES-192 is chosen. This is also seems to
be in upstream.



-- 
Richard Chan
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