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LibTLS: Add Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) support

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This adds support for the Elliptic Curve Diffie-Hellman Ephemeral key
exchange, using the X25519 elliptic curve. This means that the
ECDHE_RSA_WITH_AES_128_GCM_SHA256 and ECDHE_RSA_WITH_AES_256_GCM_SHA384
cipher suites are now supported.

Currently, only the X25519 elliptic curve is supported in combination
with the uncompressed elliptic curve point format. However, since the
X25519 is the recommended curve, basically every server supports this.
Furthermore, the uncompressed point format is required by the TLS
specification, which means any server with EC support will support the
uncompressed format.

Like the implementation of the normal Diffie-Hellman Ephemeral key
exchange, this implementation does not currently validate the signature
of the public key sent by the server.
This commit is contained in:
Michiel Visser 2022-02-17 19:43:42 +01:00 • committed by Ali Mohammad Pur
parent be07892fea
commit 7ab4337721
5 changed files with 176 additions and 10 deletions
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25
Userland/Libraries/LibTLS/Handshake.cpp
View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2020, Ali Mohammad Pur <mpfard@serenityos.org>
* Copyright (c) 2022, Michiel Visser <opensource@webmichiel.nl>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -71,12 +72,20 @@ ByteBuffer TLSv12::build_hello()
if (!m_context.extensions.SNI.is_null() && m_context.options.use_sni)
sni_length = m_context.extensions.SNI.length();
auto elliptic_curves_length = 2 * m_context.options.elliptic_curves.size();
auto supported_ec_point_formats_length = m_context.options.supported_ec_point_formats.size();
bool supports_elliptic_curves = elliptic_curves_length && supported_ec_point_formats_length;
// signature_algorithms: 2b extension ID, 2b extension length, 2b vector length, 2xN signatures and hashes
extension_length += 2 + 2 + 2 + 2 * m_context.options.supported_signature_algorithms.size();
if (sni_length)
extension_length += sni_length + 9;
// Only send elliptic_curves and ec_point_formats extensions if both are supported
if (supports_elliptic_curves)
extension_length += 6 + elliptic_curves_length + 5 + supported_ec_point_formats_length;
builder.append((u16)extension_length);
if (sni_length) {
@ -105,6 +114,22 @@ ByteBuffer TLSv12::build_hello()
builder.append((u8)entry.signature);
}
if (supports_elliptic_curves) {
// elliptic_curves extension
builder.append((u16)HandshakeExtension::EllipticCurves);
builder.append((u16)(2 + elliptic_curves_length));
builder.append((u16)elliptic_curves_length);
for (auto& curve : m_context.options.elliptic_curves)
builder.append((u16)curve);
// ec_point_formats extension
builder.append((u16)HandshakeExtension::ECPointFormats);
builder.append((u16)(1 + supported_ec_point_formats_length));
builder.append((u8)supported_ec_point_formats_length);
for (auto& format : m_context.options.supported_ec_point_formats)
builder.append((u8)format);
}
if (alpn_length) {
// TODO
VERIFY_NOT_REACHED();