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Implement decryption handler for SRTP

This commit is contained in:
Aaro Altonen 2020-08-12 16:48:55 +03:00
parent 359e84076c
commit 0bbe6966f1
2 changed files with 61 additions and 0 deletions
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3
include/srtp.hh
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@ -156,6 +156,9 @@ namespace uvg_rtp {
/* Get reference to the SRTP context (including session keys) */
srtp_ctx_t& get_ctx();
/* Decrypt the payload and verify authentication tag (if enabled) */
static rtp_error_t recv_packet_handler(void *arg, int flags, frame::rtp_frame **out);
/* Encrypt the payload and add authentication tag (if enabled) */
static rtp_error_t send_packet_handler_buf(void *arg, ssize_t len, void *buf);
static rtp_error_t send_packet_handler_vec(void *arg, std::vector<std::pair<size_t, uint8_t *>>& buffers);

58
src/srtp.cc
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@ -207,6 +207,64 @@ rtp_error_t uvg_rtp::srtp::init_user(int type, int flags, uint8_t *key, uint8_t
return __init(type, flags);
}
rtp_error_t uvg_rtp::srtp::recv_packet_handler(void *arg, int flags, frame::rtp_frame **out)
{
uvg_rtp::srtp *srtp = (uvg_rtp::srtp *)arg;
uvg_rtp::srtp_ctx_t ctx = srtp->get_ctx();
uvg_rtp::frame::rtp_frame *frame = *out;
if (srtp->use_null_cipher())
return RTP_PKT_NOT_HANDLED;
uint8_t iv[16] = { 0 };
uint16_t seq = frame->header.seq;
uint32_t ssrc = frame->header.ssrc;
uint64_t index = (((uint64_t)ctx.roc) << 16) + seq;
uint64_t digest = 0;
/* Sequence number has wrapped around, update Roll-over Counter */
if (seq == 0xffff)
ctx.roc++;
if (srtp->create_iv(iv, frame->header.ssrc, index, ctx.key_ctx.remote.salt_key) != RTP_OK) {
LOG_ERROR("Failed to create IV, unable to encrypt the RTP packet!");
return RTP_INVALID_VALUE;
}
uvg_rtp::crypto::aes::ctr ctr(ctx.key_ctx.remote.enc_key, sizeof(ctx.key_ctx.remote.enc_key), iv);
/* exit early if RTP packet authentication is disabled... */
if (!srtp->authenticate_rtp()) {
ctr.decrypt(frame->payload, frame->payload, frame->payload_len);
return RTP_OK;
}
/* ... otherwise calculate authentication tag for the packet
* and compare it against the one we received */
auto hmac_sha1 = uvg_rtp::crypto::hmac::sha1(ctx.key_ctx.remote.auth_key, AES_KEY_LENGTH);
hmac_sha1.update((uint8_t *)frame, frame->payload_len - AUTH_TAG_LENGTH);
hmac_sha1.update((uint8_t *)&ctx.roc, sizeof(ctx.roc));
hmac_sha1.final((uint8_t *)&digest);
uint8_t *tmp_buffer = (uint8_t *)frame;
if (memcmp(&digest, &frame[frame->payload_len - AUTH_TAG_LENGTH], AUTH_TAG_LENGTH)) {
LOG_ERROR("Authentication tag mismatch!");
return RTP_AUTH_TAG_MISMATCH;
}
size_t size_ = frame->payload_len - sizeof(uvg_rtp::frame::rtp_header) - 8;
uint8_t *new_buffer = new uint8_t[size_];
ctr.decrypt(new_buffer, frame->payload, size_);
memset(frame->payload, 0, frame->payload_len);
memcpy(frame->payload, new_buffer, size_);
delete[] new_buffer;
return RTP_OK;
}
rtp_error_t uvg_rtp::srtp::send_packet_handler_buf(void *arg, ssize_t len, void *buf)
{
auto srtp = (uvg_rtp::srtp *)arg;