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