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LibTLS: Implement the DHE_RSA key exchange algorithm

Browse source 
This adds two methods, handle_dhe_rsa_server_key_exchange and
build_dhe_rsa_pre_master_secret, to TLSv12 and a struct,
server_diffie_hellman_params, to Context, which are used to implement
the DHE_RSA key exchange algorithm. This grants us the benefits of
forward secrecy and access to sites which support DHE_RSA.

It is worth noting that the signature of the server provided
Diffie-Hellman parameters is not currently validated. This will need to
be addressed to prevent man-in-the-middle attacks.
This commit is contained in:
Samuel Bowman 2021-08-12 15:25:47 -04:00 • committed by Ali Mohammad Pur
parent 020bfc9d93
commit b288016bbc
3 changed files with 75 additions and 5 deletions
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30
Userland/Libraries/LibTLS/HandshakeServer.cpp
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@ -199,7 +199,7 @@ ByteBuffer TLSv12::build_server_key_exchange()
return {};
}
ssize_t TLSv12::handle_server_key_exchange(ReadonlyBytes)
ssize_t TLSv12::handle_server_key_exchange(ReadonlyBytes buffer)
{
switch (get_key_exchange_algorithm(m_context.cipher)) {
case KeyExchangeAlgorithm::RSA:
@ -214,8 +214,7 @@ ssize_t TLSv12::handle_server_key_exchange(ReadonlyBytes)
TODO();
break;
case KeyExchangeAlgorithm::DHE_RSA:
dbgln("Server key exchange for DHE_RSA is not implemented");
TODO();
handle_dhe_rsa_server_key_exchange(buffer);
break;
case KeyExchangeAlgorithm::DH_anon:
dbgln("Server key exchange for DH_anon is not implemented");
@ -237,4 +236,29 @@ ssize_t TLSv12::handle_server_key_exchange(ReadonlyBytes)
return 0;
}
ssize_t TLSv12::handle_dhe_rsa_server_key_exchange(ReadonlyBytes buffer)
{
auto dh_p_length = AK::convert_between_host_and_network_endian(ByteReader::load16(buffer.offset_pointer(3)));
auto dh_p = buffer.slice(5, dh_p_length);
m_context.server_diffie_hellman_params.p = ByteBuffer::copy(dh_p.data(), dh_p.size());
auto dh_g_length = AK::convert_between_host_and_network_endian(ByteReader::load16(buffer.offset_pointer(5 + dh_p_length)));
auto dh_g = buffer.slice(7 + dh_p_length, dh_g_length);
m_context.server_diffie_hellman_params.g = ByteBuffer::copy(dh_g.data(), dh_g.size());
auto dh_Ys_length = AK::convert_between_host_and_network_endian(ByteReader::load16(buffer.offset_pointer(7 + dh_p_length + dh_g_length)));
auto dh_Ys = buffer.slice(9 + dh_p_length + dh_g_length, dh_Ys_length);
m_context.server_diffie_hellman_params.Ys = ByteBuffer::copy(dh_Ys.data(), dh_Ys.size());
if constexpr (TLS_DEBUG) {
dbgln("dh_p: {:hex-dump}", dh_p);
dbgln("dh_g: {:hex-dump}", dh_g);
dbgln("dh_Ys: {:hex-dump}", dh_Ys);
}
// FIXME: Validate signature of Diffie-Hellman parameters as defined in RFC 5246 section 7.4.3.
return 0;
}
}