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fix(tls): require a verified leaf key for CertificateVerify #10

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fix(tls): require a verified leaf key for CertificateVerify #10

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93 changes: 87 additions & 6 deletions src/quic/tls13.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -1115,11 +1115,7 @@ pub const Tls13Handshake = struct {
if (cert_index == 0) {
// Leaf cert: extract public key for CertificateVerify
const pub_key = parsed.pubKey();
if (pub_key.len <= self.leaf_pub_key_buf.len) {
@memcpy(self.leaf_pub_key_buf[0..pub_key.len], pub_key);
self.leaf_pub_key_len = @intCast(pub_key.len);
self.leaf_pub_key_algo = std.meta.activeTag(parsed.pub_key_algo);
}
try self.storeLeafPublicKey(pub_key, std.meta.activeTag(parsed.pub_key_algo));

// Verify hostname if SNI was set
if (self.config.server_name) |server_name| {
Expand Down Expand Up @@ -1162,6 +1158,8 @@ pub const Tls13Handshake = struct {
cert_index += 1;
}

if (!self.config.skip_cert_verify and cert_index == 0) return error.BadCertificate;

self.transcript.update(msg);
self.state = .client_wait_certificate_verify;
return ._continue;
Expand All @@ -1171,8 +1169,9 @@ pub const Tls13Handshake = struct {
const msg = self.readHandshakeMsg() orelse return .wait_for_data;

if (msg[0] != @intFromEnum(MsgType.certificate_verify)) return error.UnexpectedMessage;
if (!self.config.skip_cert_verify and self.leaf_pub_key_len == 0) return error.BadCertificateVerify;

if (!self.config.skip_cert_verify and self.leaf_pub_key_len > 0) {
if (!self.config.skip_cert_verify) {
// Get transcript hash BEFORE updating with CertificateVerify
const transcript_hash = self.transcript.current();

Expand Down Expand Up @@ -1206,6 +1205,17 @@ pub const Tls13Handshake = struct {
return ._continue;
}

fn storeLeafPublicKey(
self: *Tls13Handshake,
pub_key: []const u8,
pub_key_algo: Certificate.AlgorithmCategory,
) HandshakeError!void {
if (pub_key.len == 0 or pub_key.len > self.leaf_pub_key_buf.len) return error.BadCertificate;
@memcpy(self.leaf_pub_key_buf[0..pub_key.len], pub_key);
self.leaf_pub_key_len = @intCast(pub_key.len);
self.leaf_pub_key_algo = pub_key_algo;
}

fn clientProcessFinished(self: *Tls13Handshake) !Action {
const msg = self.readHandshakeMsg() orelse return .wait_for_data;

Expand Down Expand Up @@ -3104,6 +3114,77 @@ test "loopback PSK resumption: two handshakes with session ticket" {
);
}

test "clientProcessCertificate rejects empty certificate list when verification enabled" {
const tp = transport_params.TransportParams{
.initial_max_data = 1048576,
.initial_max_streams_bidi = 100,
};

const client_config = TlsConfig{
.cert_chain_der = &.{},
.private_key_bytes = &.{},
.alpn = &[_][]const u8{"h3"},
.server_name = "localhost",
.skip_cert_verify = false,
};

var handshake = Tls13Handshake.initClient(client_config, tp);

var buf: [64]u8 = undefined;
const cert_msg = try buildCertificate(&buf, &.{});
handshake.provideData(cert_msg);

try std.testing.expectError(error.BadCertificate, handshake.clientProcessCertificate());
}

test "storeLeafPublicKey rejects oversized verification keys" {
const tp = transport_params.TransportParams{
.initial_max_data = 1048576,
.initial_max_streams_bidi = 100,
};

const client_config = TlsConfig{
.cert_chain_der = &.{},
.private_key_bytes = &.{},
.alpn = &[_][]const u8{"h3"},
.server_name = "localhost",
.skip_cert_verify = false,
};

var handshake = Tls13Handshake.initClient(client_config, tp);
var oversized: [601]u8 = .{0x42} ** 601;

try std.testing.expectError(
error.BadCertificate,
handshake.storeLeafPublicKey(&oversized, .X9_62_id_ecPublicKey),
);
}

test "clientProcessCertificateVerify rejects missing leaf key when verification enabled" {
const tp = transport_params.TransportParams{
.initial_max_data = 1048576,
.initial_max_streams_bidi = 100,
};

const client_config = TlsConfig{
.cert_chain_der = &.{},
.private_key_bytes = &.{},
.alpn = &[_][]const u8{"h3"},
.server_name = "localhost",
.skip_cert_verify = false,
};

var handshake = Tls13Handshake.initClient(client_config, tp);
handshake.provideData(&[_]u8{
@intFromEnum(MsgType.certificate_verify),
0,
0,
0,
});

try std.testing.expectError(error.BadCertificateVerify, handshake.clientProcessCertificateVerify());
}

// NewSessionTicket roundtrip test
test "NewSessionTicket: build and parse roundtrip" {
const psk: [32]u8 = .{0x55} ** 32;
Expand Down
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