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TLS: use distinct ciphersuites and extensions for TLS 1.2 and TLS 1.3 #24316

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TLS: use distinct ciphersuites and extensions for TLS 1.2 and TLS 1.3 #24316

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Use distinct ciphersuites and key exchange mechanisms for TLS 1.2 and…
jedisct1 Jul 1, 2025
a9c9e83
Try with TLS 1.2 if a TLS 1.3 handshake fails
jedisct1 Jul 1, 2025
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103 changes: 68 additions & 35 deletions lib/std/crypto/tls/Client.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -180,11 +180,8 @@ pub fn InitError(comptime Stream: type) type {
};
}

/// Initiates a TLS handshake and establishes a TLSv1.2 or TLSv1.3 session with `stream`, which
/// must conform to `StreamInterface`.
///
/// `host` is only borrowed during this function call.
pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client {
/// Internal function to initiate TLS handshake with specific cipher suites and protocol versions.
fn initWithCipherSuites(stream: anytype, options: Options, cipher_suite_array: anytype, comptime supported_versions: anytype, comptime tls12_only: bool) InitError(@TypeOf(stream))!Client {
const host = switch (options.host) {
.no_verification => "",
.explicit => |host| host,
Expand All @@ -203,10 +200,7 @@ pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client
error.IdentityElement => return error.InsufficientEntropy,
};

const extensions_payload = tls.extension(.supported_versions, array(u8, tls.ProtocolVersion, .{
.tls_1_3,
.tls_1_2,
})) ++ tls.extension(.signature_algorithms, array(u16, tls.SignatureScheme, .{
const signature_algorithms = array(u16, tls.SignatureScheme, .{
.ecdsa_secp256r1_sha256,
.ecdsa_secp384r1_sha384,
.rsa_pkcs1_sha256,
Expand All @@ -220,25 +214,43 @@ pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client
.rsa_pss_pss_sha512,
.rsa_pkcs1_sha1,
.ed25519,
})) ++ tls.extension(.supported_groups, array(u16, tls.NamedGroup, .{
.x25519_ml_kem768,
.secp256r1,
.secp384r1,
.x25519,
})) ++ tls.extension(.psk_key_exchange_modes, array(u8, tls.PskKeyExchangeMode, .{
.psk_dhe_ke,
})) ++ tls.extension(.key_share, array(
u16,
u8,
int(u16, @intFromEnum(tls.NamedGroup.x25519_ml_kem768)) ++
array(u16, u8, key_share.ml_kem768_kp.public_key.toBytes() ++ key_share.x25519_kp.public_key) ++
int(u16, @intFromEnum(tls.NamedGroup.secp256r1)) ++
array(u16, u8, key_share.secp256r1_kp.public_key.toUncompressedSec1()) ++
int(u16, @intFromEnum(tls.NamedGroup.secp384r1)) ++
array(u16, u8, key_share.secp384r1_kp.public_key.toUncompressedSec1()) ++
int(u16, @intFromEnum(tls.NamedGroup.x25519)) ++
array(u16, u8, key_share.x25519_kp.public_key),
));
});

const supported_groups = if (tls12_only)
array(u16, tls.NamedGroup, .{
.secp256r1,
.secp384r1,
})
else
array(u16, tls.NamedGroup, .{
.x25519_ml_kem768,
.secp256r1,
.secp384r1,
.x25519,
});

const base_extensions = tls.extension(.signature_algorithms, signature_algorithms) ++
tls.extension(.supported_groups, supported_groups);

const extensions_payload = if (tls12_only)
base_extensions
else
tls.extension(.supported_versions, array(u8, tls.ProtocolVersion, supported_versions)) ++
base_extensions ++
tls.extension(.psk_key_exchange_modes, array(u8, tls.PskKeyExchangeMode, .{
.psk_dhe_ke,
})) ++ tls.extension(.key_share, array(
u16,
u8,
int(u16, @intFromEnum(tls.NamedGroup.x25519_ml_kem768)) ++
array(u16, u8, key_share.ml_kem768_kp.public_key.toBytes() ++ key_share.x25519_kp.public_key) ++
int(u16, @intFromEnum(tls.NamedGroup.secp256r1)) ++
array(u16, u8, key_share.secp256r1_kp.public_key.toUncompressedSec1()) ++
int(u16, @intFromEnum(tls.NamedGroup.secp384r1)) ++
array(u16, u8, key_share.secp384r1_kp.public_key.toUncompressedSec1()) ++
int(u16, @intFromEnum(tls.NamedGroup.x25519)) ++
array(u16, u8, key_share.x25519_kp.public_key),
));
const server_name_extension = int(u16, @intFromEnum(tls.ExtensionType.server_name)) ++
int(u16, 2 + 1 + 2 + host_len) ++ // byte length of this extension payload
int(u16, 1 + 2 + host_len) ++ // server_name_list byte count
Expand All @@ -258,7 +270,7 @@ pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client
int(u16, @intFromEnum(tls.ProtocolVersion.tls_1_2)) ++
client_hello_rand ++
[1]u8{32} ++ legacy_session_id ++
cipher_suites ++
cipher_suite_array ++
array(u8, tls.CompressionMethod, .{.null}) ++
extensions_header;

Expand Down Expand Up @@ -897,6 +909,20 @@ pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client
}
}

/// Initiates a TLS handshake and establishes a TLSv1.2 or TLSv1.3 session with `stream`, which
/// must conform to `StreamInterface`.
///
/// `host` is only borrowed during this function call.
pub fn init(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client {
return initWithCipherSuites(stream, options, tls_1_3_cipher_suites, .{ .tls_1_3, .tls_1_2 }, false);
}

/// Initiates a TLS handshake restricted to TLS 1.2-compatible cipher suites only.
/// This is used as a fallback when the server doesn't support TLS 1.3 cipher suites.
pub fn initTls12Only(stream: anytype, options: Options) InitError(@TypeOf(stream))!Client {
return initWithCipherSuites(stream, options, tls_1_2_cipher_suites, .{.tls_1_2}, true);
}

/// Sends TLS-encrypted data to `stream`, which must conform to `StreamInterface`.
/// Returns the number of cleartext bytes sent, which may be fewer than `bytes.len`.
pub fn write(c: *Client, stream: anytype, bytes: []const u8) !usize {
Expand Down Expand Up @@ -1932,26 +1958,33 @@ fn limitVecs(iovecs: []std.posix.iovec, len: usize) []std.posix.iovec {
/// aegis-256: 461 MiB/s
/// aes128-gcm: 138 MiB/s
/// aes256-gcm: 120 MiB/s
const cipher_suites = if (crypto.core.aes.has_hardware_support)
const tls_1_3_cipher_suites = if (crypto.core.aes.has_hardware_support)
array(u16, tls.CipherSuite, .{
.AEGIS_128L_SHA256,
.AEGIS_256_SHA512,
.AES_128_GCM_SHA256,
.ECDHE_RSA_WITH_AES_128_GCM_SHA256,
.AES_256_GCM_SHA384,
.ECDHE_RSA_WITH_AES_256_GCM_SHA384,
.CHACHA20_POLY1305_SHA256,
.ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
})
else
array(u16, tls.CipherSuite, .{
.CHACHA20_POLY1305_SHA256,
.ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
.AEGIS_128L_SHA256,
.AEGIS_256_SHA512,
.AES_128_GCM_SHA256,
.ECDHE_RSA_WITH_AES_128_GCM_SHA256,
.AES_256_GCM_SHA384,
});

const tls_1_2_cipher_suites = if (crypto.core.aes.has_hardware_support)
array(u16, tls.CipherSuite, .{
.ECDHE_RSA_WITH_AES_128_GCM_SHA256,
.ECDHE_RSA_WITH_AES_256_GCM_SHA384,
.ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
})
else
array(u16, tls.CipherSuite, .{
.ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
.ECDHE_RSA_WITH_AES_128_GCM_SHA256,
.ECDHE_RSA_WITH_AES_256_GCM_SHA384,
});

Expand Down
31 changes: 30 additions & 1 deletion lib/std/http/Client.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -1376,7 +1376,36 @@ pub fn connectTcp(client: *Client, host: []const u8, port: u16, protocol: Connec
.host = .{ .explicit = host },
.ca = .{ .bundle = client.ca_bundle },
.ssl_key_log_file = ssl_key_log_file,
}) catch return error.TlsInitializationFailed;
}) catch |err| switch (err) {
// Try TLS 1.2 fallback with new connection for compatibility with servers that don't support TLS 1.3 extensions
error.TlsAlertHandshakeFailure, error.TlsAlertIllegalParameter, error.TlsAlertDecodeError => blk: {
// Close the corrupted connection and create a new one
stream.close();

const fallback_stream = net.tcpConnectToHost(client.allocator, host, port) catch |tcp_err| switch (tcp_err) {
error.ConnectionRefused => return error.ConnectionRefused,
error.NetworkUnreachable => return error.NetworkUnreachable,
error.ConnectionTimedOut => return error.ConnectionTimedOut,
error.ConnectionResetByPeer => return error.ConnectionResetByPeer,
error.TemporaryNameServerFailure => return error.TemporaryNameServerFailure,
error.NameServerFailure => return error.NameServerFailure,
error.UnknownHostName => return error.UnknownHostName,
error.HostLacksNetworkAddresses => return error.HostLacksNetworkAddresses,
else => return error.UnexpectedConnectFailure,
};
errdefer fallback_stream.close();

// Update connection to use new stream
conn.stream = fallback_stream;

break :blk std.crypto.tls.Client.initTls12Only(fallback_stream, .{
.host = .{ .explicit = host },
.ca = .{ .bundle = client.ca_bundle },
.ssl_key_log_file = ssl_key_log_file,
}) catch return error.TlsInitializationFailed;
},
else => return error.TlsInitializationFailed,
};
// This is appropriate for HTTPS because the HTTP headers contain
// the content length which is used to detect truncation attacks.
conn.tls_client.allow_truncation_attacks = true;
Expand Down
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