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[FCE-3227] Fix DTLS fingerprint not being validated in certain cases #250

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Merged
sgfn merged 2 commits into from
May 4, 2026
Merged

[FCE-3227] Fix DTLS fingerprint not being validated in certain cases #250

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a6ede8c
[FCE-3227] Fix DTLS fingerprint not being validated in certain cases
sgfn Apr 27, 2026
d0c6ca3
fix tests
sgfn Apr 27, 2026
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55 changes: 29 additions & 26 deletions lib/ex_webrtc/dtls_transport.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -481,34 +481,10 @@ defmodule ExWebRTC.DTLSTransport do
{:ok, state}

{:handshake_finished, lkm, rkm, profile, packets} ->
Logger.debug("DTLS handshake finished")
state = update_remote_cert_info(state)
:ok = do_send(state, packets)

peer_fingerprint =
state.dtls
|> ExDTLS.get_peer_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

if peer_fingerprint == state.peer_fingerprint do
:ok = setup_srtp(state, lkm, rkm, profile)
state = update_dtls_state(state, :connected)
state = flush_buffered_remote_rtp_packets(state)
{:ok, state}
else
Logger.debug("Non-matching peer cert fingerprint.")
state = update_dtls_state(state, :failed)
{:ok, state}
end
handle_handshake_finished(state, lkm, rkm, profile, packets)

{:handshake_finished, lkm, rkm, profile} ->
Logger.debug("DTLS handshake finished")
:ok = setup_srtp(state, lkm, rkm, profile)
state = update_dtls_state(state, :connected)
state = flush_buffered_remote_rtp_packets(state)
state = update_remote_cert_info(state)
{:ok, state}
handle_handshake_finished(state, lkm, rkm, profile)

:handshake_want_read ->
{:ok, state}
Expand Down Expand Up @@ -554,6 +530,33 @@ defmodule ExWebRTC.DTLSTransport do
{:ok, state}
end

defp handle_handshake_finished(state, lkm, rkm, profile, packets \\ []) do
Logger.debug("DTLS handshake finished")

if peer_fingerprint_matching?(state) do
:ok = setup_srtp(state, lkm, rkm, profile)
state = update_dtls_state(state, :connected)
state = flush_buffered_remote_rtp_packets(state)
state = update_remote_cert_info(state)
:ok = do_send(state, packets)
{:ok, state}
else
Logger.debug("Non-matching peer cert fingerprint.")
state = update_dtls_state(state, :failed)
{:ok, state}
end
end

defp peer_fingerprint_matching?(%{peer_fingerprint: expected_fp} = state) do
actual_fp =
state.dtls
|> ExDTLS.get_peer_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

expected_fp == actual_fp
end

defp setup_srtp(state, local_keying_material, remote_keying_material, profile) do
{:ok, crypto_profile} =
ExLibSRTP.Policy.crypto_profile_from_dtls_srtp_protection_profile(profile)
Expand Down
41 changes: 36 additions & 5 deletions test/ex_webrtc/dtls_transport_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@

@impl true
def handle_call(:close, _from, state) do
# TODO implement

Check warning on line 97 in test/ex_webrtc/dtls_transport_test.exs

View workflow job for this annotation

GitHub Actions / CI on OTP 27 / Elixir 1.17 

Found a TODO tag in a comment: # TODO implement
{:reply, :ok, state}
end

Expand Down Expand Up @@ -163,8 +163,15 @@
ice_transport: ice_transport,
ice_pid: ice_pid
} do
:ok = DTLSTransport.start_dtls(dtls, :active, @fingerprint)
remote_dtls = ExDTLS.init(mode: :server, dtls_srtp: true)

remote_fingerprint =
remote_dtls
|> ExDTLS.get_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

:ok = DTLSTransport.start_dtls(dtls, :active, remote_fingerprint)
:ok = DTLSTransport.set_ice_connected(dtls)

# perform DTLS-SRTP handshake
Expand Down Expand Up @@ -240,9 +247,15 @@
ice_transport: ice_transport,
ice_pid: ice_pid
} do
:ok = DTLSTransport.start_dtls(dtls, :active, @fingerprint)
remote_dtls = ExDTLS.init(mode: :server, dtls_srtp: true)

remote_fingerprint =
remote_dtls
|> ExDTLS.get_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

:ok = DTLSTransport.start_dtls(dtls, :active, remote_fingerprint)
:ok = DTLSTransport.set_ice_connected(dtls)

assert {:ok, _, _, _} = check_handshake(dtls, ice_transport, ice_pid, remote_dtls)
Expand Down Expand Up @@ -296,9 +309,15 @@
ice_transport: ice_transport,
ice_pid: ice_pid
} do
:ok = DTLSTransport.start_dtls(dtls, :active, @fingerprint)
remote_dtls = ExDTLS.init(mode: :server, dtls_srtp: true)

remote_fingerprint =
remote_dtls
|> ExDTLS.get_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

:ok = DTLSTransport.start_dtls(dtls, :active, remote_fingerprint)
:ok = DTLSTransport.set_ice_connected(dtls)

assert {:ok, _, _, _} = check_handshake(dtls, ice_transport, ice_pid, remote_dtls)
Expand Down Expand Up @@ -328,9 +347,15 @@
ice_transport: ice_transport,
ice_pid: ice_pid
} do
:ok = DTLSTransport.start_dtls(dtls, :active, @fingerprint)
remote_dtls = ExDTLS.init(mode: :server, dtls_srtp: true)

remote_fingerprint =
remote_dtls
|> ExDTLS.get_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

:ok = DTLSTransport.start_dtls(dtls, :active, remote_fingerprint)
:ok = DTLSTransport.set_ice_connected(dtls)

# perform DTLS-SRTP handshake
Expand Down Expand Up @@ -380,9 +405,15 @@
ice_transport: ice_transport,
ice_pid: ice_pid
} do
:ok = DTLSTransport.start_dtls(dtls, :active, @fingerprint)
remote_dtls = ExDTLS.init(mode: :server, dtls_srtp: true)

remote_fingerprint =
remote_dtls
|> ExDTLS.get_cert()
|> ExDTLS.get_cert_fingerprint()
|> Utils.hex_dump()

:ok = DTLSTransport.start_dtls(dtls, :active, remote_fingerprint)
:ok = DTLSTransport.set_ice_connected(dtls)

# perform DTLS-SRTP handshake
Expand Down
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