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boringssl/ssl/encrypted_client_hello.cc

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/* Copyright (c) 2021, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <openssl/ssl.h>
#include <assert.h>
#include <string.h>
#include <algorithm>
#include <utility>
#include <openssl/aead.h>
#include <openssl/bytestring.h>
#include <openssl/curve25519.h>
#include <openssl/err.h>
#include <openssl/hkdf.h>
#include <openssl/hpke.h>
#include <openssl/rand.h>
#include "internal.h"
BSSL_NAMESPACE_BEGIN
// ECH reuses the extension code point for the version number.
static constexpr uint16_t kECHConfigVersion =
TLSEXT_TYPE_encrypted_client_hello;
static const decltype(&EVP_hpke_aes_128_gcm) kSupportedAEADs[] = {
&EVP_hpke_aes_128_gcm,
&EVP_hpke_aes_256_gcm,
&EVP_hpke_chacha20_poly1305,
};
static const EVP_HPKE_AEAD *get_ech_aead(uint16_t aead_id) {
for (const auto aead_func : kSupportedAEADs) {
const EVP_HPKE_AEAD *aead = aead_func();
if (aead_id == EVP_HPKE_AEAD_id(aead)) {
return aead;
}
}
return nullptr;
}
// ssl_client_hello_write_without_extensions serializes |client_hello| into
// |out|, omitting the length-prefixed extensions. It serializes individual
// fields, starting with |client_hello->version|, and ignores the
// |client_hello->client_hello| field. It returns true on success and false on
// failure.
static bool ssl_client_hello_write_without_extensions(
const SSL_CLIENT_HELLO *client_hello, CBB *out) {
CBB cbb;
if (!CBB_add_u16(out, client_hello->version) ||
!CBB_add_bytes(out, client_hello->random, client_hello->random_len) ||
!CBB_add_u8_length_prefixed(out, &cbb) ||
!CBB_add_bytes(&cbb, client_hello->session_id,
client_hello->session_id_len) ||
!CBB_add_u16_length_prefixed(out, &cbb) ||
!CBB_add_bytes(&cbb, client_hello->cipher_suites,
client_hello->cipher_suites_len) ||
!CBB_add_u8_length_prefixed(out, &cbb) ||
!CBB_add_bytes(&cbb, client_hello->compression_methods,
client_hello->compression_methods_len) ||
!CBB_flush(out)) {
return false;
}
return true;
}
static bool is_valid_client_hello_inner(SSL *ssl, uint8_t *out_alert,
Span<const uint8_t> body) {
// See draft-ietf-tls-esni-13, section 7.1.
SSL_CLIENT_HELLO client_hello;
CBS extension;
if (!ssl_client_hello_init(ssl, &client_hello, body) ||
!ssl_client_hello_get_extension(&client_hello, &extension,
TLSEXT_TYPE_encrypted_client_hello) ||
CBS_len(&extension) != 1 || //
CBS_data(&extension)[0] != ECH_CLIENT_INNER ||
!ssl_client_hello_get_extension(&client_hello, &extension,
TLSEXT_TYPE_supported_versions)) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_CLIENT_HELLO_INNER);
return false;
}
// Parse supported_versions and reject TLS versions prior to TLS 1.3. Older
// versions are incompatible with ECH.
CBS versions;
if (!CBS_get_u8_length_prefixed(&extension, &versions) ||
CBS_len(&extension) != 0 || //
CBS_len(&versions) == 0) {
*out_alert = SSL_AD_DECODE_ERROR;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
while (CBS_len(&versions) != 0) {
uint16_t version;
if (!CBS_get_u16(&versions, &version)) {
*out_alert = SSL_AD_DECODE_ERROR;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (version == SSL3_VERSION || version == TLS1_VERSION ||
version == TLS1_1_VERSION || version == TLS1_2_VERSION ||
version == DTLS1_VERSION || version == DTLS1_2_VERSION) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_CLIENT_HELLO_INNER);
return false;
}
}
return true;
}
bool ssl_decode_client_hello_inner(
SSL *ssl, uint8_t *out_alert, Array<uint8_t> *out_client_hello_inner,
Span<const uint8_t> encoded_client_hello_inner,
const SSL_CLIENT_HELLO *client_hello_outer) {
SSL_CLIENT_HELLO client_hello_inner;
CBS cbs = encoded_client_hello_inner;
if (!ssl_parse_client_hello_with_trailing_data(ssl, &cbs,
&client_hello_inner)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// The remaining data is padding.
uint8_t padding;
while (CBS_get_u8(&cbs, &padding)) {
if (padding != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
return false;
}
}
// TLS 1.3 ClientHellos must have extensions, and EncodedClientHelloInners use
// ClientHelloOuter's session_id.
if (client_hello_inner.extensions_len == 0 ||
client_hello_inner.session_id_len != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
client_hello_inner.session_id = client_hello_outer->session_id;
client_hello_inner.session_id_len = client_hello_outer->session_id_len;
// Begin serializing a message containing the ClientHelloInner in |cbb|.
ScopedCBB cbb;
CBB body, extensions_cbb;
if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_CLIENT_HELLO) ||
!ssl_client_hello_write_without_extensions(&client_hello_inner, &body) ||
!CBB_add_u16_length_prefixed(&body, &extensions_cbb)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
auto inner_extensions = MakeConstSpan(client_hello_inner.extensions,
client_hello_inner.extensions_len);
CBS ext_list_wrapper;
if (!ssl_client_hello_get_extension(&client_hello_inner, &ext_list_wrapper,
TLSEXT_TYPE_ech_outer_extensions)) {
// No ech_outer_extensions. Copy everything.
if (!CBB_add_bytes(&extensions_cbb, inner_extensions.data(),
inner_extensions.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
} else {
const size_t offset = CBS_data(&ext_list_wrapper) - inner_extensions.data();
auto inner_extensions_before =
inner_extensions.subspan(0, offset - 4 /* extension header */);
auto inner_extensions_after =
inner_extensions.subspan(offset + CBS_len(&ext_list_wrapper));
if (!CBB_add_bytes(&extensions_cbb, inner_extensions_before.data(),
inner_extensions_before.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
// Expand ech_outer_extensions. See draft-ietf-tls-esni-13, Appendix B.
CBS ext_list;
if (!CBS_get_u8_length_prefixed(&ext_list_wrapper, &ext_list) ||
CBS_len(&ext_list) == 0 || CBS_len(&ext_list_wrapper) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
CBS outer_extensions;
CBS_init(&outer_extensions, client_hello_outer->extensions,
client_hello_outer->extensions_len);
while (CBS_len(&ext_list) != 0) {
// Find the next extension to copy.
uint16_t want;
if (!CBS_get_u16(&ext_list, &want)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// The ECH extension itself is not in the AAD and may not be referenced.
if (want == TLSEXT_TYPE_encrypted_client_hello) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_OUTER_EXTENSION);
return false;
}
// Seek to |want| in |outer_extensions|. |ext_list| is required to match
// ClientHelloOuter in order.
uint16_t found;
CBS ext_body;
do {
if (CBS_len(&outer_extensions) == 0) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_OUTER_EXTENSION);
return false;
}
if (!CBS_get_u16(&outer_extensions, &found) ||
!CBS_get_u16_length_prefixed(&outer_extensions, &ext_body)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
} while (found != want);
// Copy the extension.
if (!CBB_add_u16(&extensions_cbb, found) ||
!CBB_add_u16(&extensions_cbb, CBS_len(&ext_body)) ||
!CBB_add_bytes(&extensions_cbb, CBS_data(&ext_body),
CBS_len(&ext_body))) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
}
if (!CBB_add_bytes(&extensions_cbb, inner_extensions_after.data(),
inner_extensions_after.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
}
if (!CBB_flush(&body)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
if (!is_valid_client_hello_inner(
ssl, out_alert, MakeConstSpan(CBB_data(&body), CBB_len(&body)))) {
return false;
}
if (!ssl->method->finish_message(ssl, cbb.get(), out_client_hello_inner)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
return true;
}
bool ssl_client_hello_decrypt(SSL_HANDSHAKE *hs, uint8_t *out_alert,
bool *out_is_decrypt_error, Array<uint8_t> *out,
const SSL_CLIENT_HELLO *client_hello_outer,
Span<const uint8_t> payload) {
*out_is_decrypt_error = false;
// The ClientHelloOuterAAD is |client_hello_outer| with |payload| (which must
// point within |client_hello_outer->extensions|) replaced with zeros. See
// draft-ietf-tls-esni-13, section 5.2.
Array<uint8_t> aad;
if (!aad.CopyFrom(MakeConstSpan(client_hello_outer->client_hello,
client_hello_outer->client_hello_len))) {
*out_alert = SSL_AD_INTERNAL_ERROR;
return false;
}
// We assert with |uintptr_t| because the comparison would be UB if they
// didn't alias.
assert(reinterpret_cast<uintptr_t>(client_hello_outer->extensions) <=
reinterpret_cast<uintptr_t>(payload.data()));
assert(reinterpret_cast<uintptr_t>(client_hello_outer->extensions +
client_hello_outer->extensions_len) >=
reinterpret_cast<uintptr_t>(payload.data() + payload.size()));
Span<uint8_t> payload_aad = MakeSpan(aad).subspan(
payload.data() - client_hello_outer->client_hello, payload.size());
OPENSSL_memset(payload_aad.data(), 0, payload_aad.size());
// Decrypt the EncodedClientHelloInner.
Array<uint8_t> encoded;
#if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
// In fuzzer mode, disable encryption to improve coverage. We reserve a short
// input to signal decryption failure, so the fuzzer can explore fallback to
// ClientHelloOuter.
const uint8_t kBadPayload[] = {0xff};
if (payload == kBadPayload) {
*out_alert = SSL_AD_DECRYPT_ERROR;
*out_is_decrypt_error = true;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED);
return false;
}
if (!encoded.CopyFrom(payload)) {
*out_alert = SSL_AD_INTERNAL_ERROR;
return false;
}
#else
if (!encoded.Init(payload.size())) {
*out_alert = SSL_AD_INTERNAL_ERROR;
return false;
}
size_t len;
if (!EVP_HPKE_CTX_open(hs->ech_hpke_ctx.get(), encoded.data(), &len,
encoded.size(), payload.data(), payload.size(),
aad.data(), aad.size())) {
*out_alert = SSL_AD_DECRYPT_ERROR;
*out_is_decrypt_error = true;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED);
return false;
}
encoded.Shrink(len);
#endif
if (!ssl_decode_client_hello_inner(hs->ssl, out_alert, out, encoded,
client_hello_outer)) {
return false;
}
ssl_do_msg_callback(hs->ssl, /*is_write=*/0, SSL3_RT_CLIENT_HELLO_INNER,
*out);
return true;
}
static bool is_hex_component(Span<const uint8_t> in) {
if (in.size() < 2 || in[0] != '0' || (in[1] != 'x' && in[1] != 'X')) {
return false;
}
for (uint8_t b : in.subspan(2)) {
if (!OPENSSL_isxdigit(b)) {
return false;
}
}
return true;
}
static bool is_decimal_component(Span<const uint8_t> in) {
if (in.empty()) {
return false;
}
for (uint8_t b : in) {
if (!('0' <= b && b <= '9')) {
return false;
}
}
return true;
}
bool ssl_is_valid_ech_public_name(Span<const uint8_t> public_name) {
// See draft-ietf-tls-esni-13, Section 4 and RFC 5890, Section 2.3.1. The
// public name must be a dot-separated sequence of LDH labels and not begin or
// end with a dot.
auto remaining = public_name;
if (remaining.empty()) {
return false;
}
Span<const uint8_t> last;
while (!remaining.empty()) {
// Find the next dot-separated component.
auto dot = std::find(remaining.begin(), remaining.end(), '.');
Span<const uint8_t> component;
if (dot == remaining.end()) {
component = remaining;
last = component;
remaining = Span<const uint8_t>();
} else {
component = remaining.subspan(0, dot - remaining.begin());
// Skip the dot.
remaining = remaining.subspan(dot - remaining.begin() + 1);
if (remaining.empty()) {
// Trailing dots are not allowed.
return false;
}
}
// |component| must be a valid LDH label. Checking for empty components also
// rejects leading dots.
if (component.empty() || component.size() > 63 ||
component.front() == '-' || component.back() == '-') {
return false;
}
for (uint8_t c : component) {
if (!OPENSSL_isalnum(c) && c != '-') {
return false;
}
}
}
// The WHATWG URL parser additionally does not allow any DNS names that end in
// a numeric component. See:
// https://url.spec.whatwg.org/#concept-host-parser
// https://url.spec.whatwg.org/#ends-in-a-number-checker
//
// The WHATWG parser is formulated in terms of parsing decimal, octal, and
// hex, along with a separate ASCII digits check. The ASCII digits check
// subsumes the decimal and octal check, so we only need to check two cases.
return !is_hex_component(last) && !is_decimal_component(last);
}
static bool parse_ech_config(CBS *cbs, ECHConfig *out, bool *out_supported,
bool all_extensions_mandatory) {
uint16_t version;
CBS orig = *cbs;
CBS contents;
if (!CBS_get_u16(cbs, &version) ||
!CBS_get_u16_length_prefixed(cbs, &contents)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (version != kECHConfigVersion) {
*out_supported = false;
return true;
}
// Make a copy of the ECHConfig and parse from it, so the results alias into
// the saved copy.
if (!out->raw.CopyFrom(
MakeConstSpan(CBS_data(&orig), CBS_len(&orig) - CBS_len(cbs)))) {
return false;
}
CBS ech_config(out->raw);
CBS public_name, public_key, cipher_suites, extensions;
if (!CBS_skip(&ech_config, 2) || // version
!CBS_get_u16_length_prefixed(&ech_config, &contents) ||
!CBS_get_u8(&contents, &out->config_id) ||
!CBS_get_u16(&contents, &out->kem_id) ||
!CBS_get_u16_length_prefixed(&contents, &public_key) ||
CBS_len(&public_key) == 0 ||
!CBS_get_u16_length_prefixed(&contents, &cipher_suites) ||
CBS_len(&cipher_suites) == 0 || CBS_len(&cipher_suites) % 4 != 0 ||
!CBS_get_u8(&contents, &out->maximum_name_length) ||
!CBS_get_u8_length_prefixed(&contents, &public_name) ||
CBS_len(&public_name) == 0 ||
!CBS_get_u16_length_prefixed(&contents, &extensions) ||
CBS_len(&contents) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (!ssl_is_valid_ech_public_name(public_name)) {
// TODO(https://crbug.com/boringssl/275): The draft says ECHConfigs with
// invalid public names should be ignored, but LDH syntax failures are
// unambiguously invalid.
*out_supported = false;
return true;
}
out->public_key = public_key;
out->public_name = public_name;
// This function does not ensure |out->kem_id| and |out->cipher_suites| use
// supported algorithms. The caller must do this.
out->cipher_suites = cipher_suites;
bool has_unknown_mandatory_extension = false;
while (CBS_len(&extensions) != 0) {
uint16_t type;
CBS body;
if (!CBS_get_u16(&extensions, &type) ||
!CBS_get_u16_length_prefixed(&extensions, &body)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// We currently do not support any extensions.
if (type & 0x8000 || all_extensions_mandatory) {
// Extension numbers with the high bit set are mandatory. Continue parsing
// to enforce syntax, but we will ultimately ignore this ECHConfig as a
// client and reject it as a server.
has_unknown_mandatory_extension = true;
}
}
*out_supported = !has_unknown_mandatory_extension;
return true;
}
bool ECHServerConfig::Init(Span<const uint8_t> ech_config,
const EVP_HPKE_KEY *key, bool is_retry_config) {
is_retry_config_ = is_retry_config;
// Parse the ECHConfig, rejecting all unsupported parameters and extensions.
// Unlike most server options, ECH's server configuration is serialized and
// configured in both the server and DNS. If the caller configures an
// unsupported parameter, this is a deployment error. To catch these errors,
// we fail early.
CBS cbs = ech_config;
bool supported;
if (!parse_ech_config(&cbs, &ech_config_, &supported,
/*all_extensions_mandatory=*/true)) {
return false;
}
if (CBS_len(&cbs) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (!supported) {
OPENSSL_PUT_ERROR(SSL, SSL_R_UNSUPPORTED_ECH_SERVER_CONFIG);
return false;
}
CBS cipher_suites = ech_config_.cipher_suites;
while (CBS_len(&cipher_suites) > 0) {
uint16_t kdf_id, aead_id;
if (!CBS_get_u16(&cipher_suites, &kdf_id) ||
!CBS_get_u16(&cipher_suites, &aead_id)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// The server promises to support every option in the ECHConfig, so reject
// any unsupported cipher suites.
if (kdf_id != EVP_HPKE_HKDF_SHA256 || get_ech_aead(aead_id) == nullptr) {
OPENSSL_PUT_ERROR(SSL, SSL_R_UNSUPPORTED_ECH_SERVER_CONFIG);
return false;
}
}
// Check the public key in the ECHConfig matches |key|.
uint8_t expected_public_key[EVP_HPKE_MAX_PUBLIC_KEY_LENGTH];
size_t expected_public_key_len;
if (!EVP_HPKE_KEY_public_key(key, expected_public_key,
&expected_public_key_len,
sizeof(expected_public_key))) {
return false;
}
if (ech_config_.kem_id != EVP_HPKE_KEM_id(EVP_HPKE_KEY_kem(key)) ||
MakeConstSpan(expected_public_key, expected_public_key_len) !=
ech_config_.public_key) {
OPENSSL_PUT_ERROR(SSL, SSL_R_ECH_SERVER_CONFIG_AND_PRIVATE_KEY_MISMATCH);
return false;
}
if (!EVP_HPKE_KEY_copy(key_.get(), key)) {
return false;
}
return true;
}
bool ECHServerConfig::SetupContext(EVP_HPKE_CTX *ctx, uint16_t kdf_id,
uint16_t aead_id,
Span<const uint8_t> enc) const {
// Check the cipher suite is supported by this ECHServerConfig.
CBS cbs(ech_config_.cipher_suites);
bool cipher_ok = false;
while (CBS_len(&cbs) != 0) {
uint16_t supported_kdf_id, supported_aead_id;
if (!CBS_get_u16(&cbs, &supported_kdf_id) ||
!CBS_get_u16(&cbs, &supported_aead_id)) {
return false;
}
if (kdf_id == supported_kdf_id && aead_id == supported_aead_id) {
cipher_ok = true;
break;
}
}
if (!cipher_ok) {
return false;
}
static const uint8_t kInfoLabel[] = "tls ech";
ScopedCBB info_cbb;
if (!CBB_init(info_cbb.get(), sizeof(kInfoLabel) + ech_config_.raw.size()) ||
!CBB_add_bytes(info_cbb.get(), kInfoLabel,
sizeof(kInfoLabel) /* includes trailing NUL */) ||
!CBB_add_bytes(info_cbb.get(), ech_config_.raw.data(),
ech_config_.raw.size())) {
return false;
}
assert(kdf_id == EVP_HPKE_HKDF_SHA256);
assert(get_ech_aead(aead_id) != NULL);
return EVP_HPKE_CTX_setup_recipient(
ctx, key_.get(), EVP_hpke_hkdf_sha256(), get_ech_aead(aead_id), enc.data(),
enc.size(), CBB_data(info_cbb.get()), CBB_len(info_cbb.get()));
}
bool ssl_is_valid_ech_config_list(Span<const uint8_t> ech_config_list) {
CBS cbs = ech_config_list, child;
if (!CBS_get_u16_length_prefixed(&cbs, &child) || //
CBS_len(&child) == 0 || //
CBS_len(&cbs) > 0) {
return false;
}
while (CBS_len(&child) > 0) {
ECHConfig ech_config;
bool supported;
if (!parse_ech_config(&child, &ech_config, &supported,
/*all_extensions_mandatory=*/false)) {
return false;
}
}
return true;
}
static bool select_ech_cipher_suite(const EVP_HPKE_KDF **out_kdf,
const EVP_HPKE_AEAD **out_aead,
Span<const uint8_t> cipher_suites,
const bool has_aes_hardware) {
const EVP_HPKE_AEAD *aead = nullptr;
CBS cbs = cipher_suites;
while (CBS_len(&cbs) != 0) {
uint16_t kdf_id, aead_id;
if (!CBS_get_u16(&cbs, &kdf_id) || //
!CBS_get_u16(&cbs, &aead_id)) {
return false;
}
// Pick the first common cipher suite, but prefer ChaCha20-Poly1305 if we
// don't have AES hardware.
const EVP_HPKE_AEAD *candidate = get_ech_aead(aead_id);
if (kdf_id != EVP_HPKE_HKDF_SHA256 || candidate == nullptr) {
continue;
}
if (aead == nullptr ||
(!has_aes_hardware && aead_id == EVP_HPKE_CHACHA20_POLY1305)) {
aead = candidate;
}
}
if (aead == nullptr) {
return false;
}
*out_kdf = EVP_hpke_hkdf_sha256();
*out_aead = aead;
return true;
}
bool ssl_select_ech_config(SSL_HANDSHAKE *hs, Span<uint8_t> out_enc,
size_t *out_enc_len) {
*out_enc_len = 0;
if (hs->max_version < TLS1_3_VERSION) {
// ECH requires TLS 1.3.
return true;
}
if (!hs->config->client_ech_config_list.empty()) {
CBS cbs = MakeConstSpan(hs->config->client_ech_config_list);
CBS child;
if (!CBS_get_u16_length_prefixed(&cbs, &child) || //
CBS_len(&child) == 0 || //
CBS_len(&cbs) > 0) {
return false;
}
// Look for the first ECHConfig with supported parameters.
while (CBS_len(&child) > 0) {
ECHConfig ech_config;
bool supported;
if (!parse_ech_config(&child, &ech_config, &supported,
/*all_extensions_mandatory=*/false)) {
return false;
}
const EVP_HPKE_KEM *kem = EVP_hpke_x25519_hkdf_sha256();
const EVP_HPKE_KDF *kdf;
const EVP_HPKE_AEAD *aead;
if (supported && //
ech_config.kem_id == EVP_HPKE_DHKEM_X25519_HKDF_SHA256 &&
select_ech_cipher_suite(&kdf, &aead, ech_config.cipher_suites,
hs->ssl->config->aes_hw_override
? hs->ssl->config->aes_hw_override_value
: EVP_has_aes_hardware())) {
ScopedCBB info;
static const uint8_t kInfoLabel[] = "tls ech"; // includes trailing NUL
if (!CBB_init(info.get(), sizeof(kInfoLabel) + ech_config.raw.size()) ||
!CBB_add_bytes(info.get(), kInfoLabel, sizeof(kInfoLabel)) ||
!CBB_add_bytes(info.get(), ech_config.raw.data(),
ech_config.raw.size())) {
return false;
}
if (!EVP_HPKE_CTX_setup_sender(
hs->ech_hpke_ctx.get(), out_enc.data(), out_enc_len,
out_enc.size(), kem, kdf, aead, ech_config.public_key.data(),
ech_config.public_key.size(), CBB_data(info.get()),
CBB_len(info.get())) ||
!hs->inner_transcript.Init()) {
return false;
}
hs->selected_ech_config = MakeUnique<ECHConfig>(std::move(ech_config));
return hs->selected_ech_config != nullptr;
}
}
}
return true;
}
static size_t aead_overhead(const EVP_HPKE_AEAD *aead) {
#if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
// TODO(https://crbug.com/boringssl/275): Having to adjust the overhead
// everywhere is tedious. Change fuzzer mode to append a fake tag but still
// otherwise be cleartext, refresh corpora, and then inline this function.
return 0;
#else
return EVP_AEAD_max_overhead(EVP_HPKE_AEAD_aead(aead));
#endif
}
// random_size returns a random value between |min| and |max|, inclusive.
static size_t random_size(size_t min, size_t max) {
assert(min < max);
size_t value;
RAND_bytes(reinterpret_cast<uint8_t *>(&value), sizeof(value));
return value % (max - min + 1) + min;
}
static bool setup_ech_grease(SSL_HANDSHAKE *hs) {
assert(!hs->selected_ech_config);
if (hs->max_version < TLS1_3_VERSION || !hs->config->ech_grease_enabled) {
return true;
}
const uint16_t kdf_id = EVP_HPKE_HKDF_SHA256;
const bool has_aes_hw = hs->ssl->config->aes_hw_override
? hs->ssl->config->aes_hw_override_value
: EVP_has_aes_hardware();
const EVP_HPKE_AEAD *aead =
has_aes_hw ? EVP_hpke_aes_128_gcm() : EVP_hpke_chacha20_poly1305();
static_assert(ssl_grease_ech_config_id < sizeof(hs->grease_seed),
"hs->grease_seed is too small");
uint8_t config_id = hs->grease_seed[ssl_grease_ech_config_id];
uint8_t enc[X25519_PUBLIC_VALUE_LEN];
uint8_t private_key_unused[X25519_PRIVATE_KEY_LEN];
X25519_keypair(enc, private_key_unused);
// To determine a plausible length for the payload, we estimate the size of a
// typical EncodedClientHelloInner without resumption:
//
// 2+32+1+2 version, random, legacy_session_id, legacy_compression_methods
// 2+4*2 cipher_suites (three TLS 1.3 ciphers, GREASE)
// 2 extensions prefix
// 5 inner encrypted_client_hello
// 4+1+2*2 supported_versions (TLS 1.3, GREASE)
// 4+1+10*2 outer_extensions (key_share, sigalgs, sct, alpn,
// supported_groups, status_request, psk_key_exchange_modes,
// compress_certificate, GREASE x2)
//
// The server_name extension has an overhead of 9 bytes. For now, arbitrarily
// estimate maximum_name_length to be between 32 and 100 bytes. Then round up
// to a multiple of 32, to match draft-ietf-tls-esni-13, section 6.1.3.
const size_t payload_len =
32 * random_size(128 / 32, 224 / 32) + aead_overhead(aead);
bssl::ScopedCBB cbb;
CBB enc_cbb, payload_cbb;
uint8_t *payload;
if (!CBB_init(cbb.get(), 256) ||
!CBB_add_u16(cbb.get(), kdf_id) ||
!CBB_add_u16(cbb.get(), EVP_HPKE_AEAD_id(aead)) ||
!CBB_add_u8(cbb.get(), config_id) ||
!CBB_add_u16_length_prefixed(cbb.get(), &enc_cbb) ||
!CBB_add_bytes(&enc_cbb, enc, sizeof(enc)) ||
!CBB_add_u16_length_prefixed(cbb.get(), &payload_cbb) ||
!CBB_add_space(&payload_cbb, &payload, payload_len) ||
!RAND_bytes(payload, payload_len) ||
!CBBFinishArray(cbb.get(), &hs->ech_client_outer)) {
return false;
}
return true;
}
bool ssl_encrypt_client_hello(SSL_HANDSHAKE *hs, Span<const uint8_t> enc) {
SSL *const ssl = hs->ssl;
if (!hs->selected_ech_config) {
return setup_ech_grease(hs);
}
// Construct ClientHelloInner and EncodedClientHelloInner. See
// draft-ietf-tls-esni-13, sections 5.1 and 6.1.
ScopedCBB cbb, encoded_cbb;
CBB body;
bool needs_psk_binder;
Array<uint8_t> hello_inner;
if (!ssl->method->init_message(ssl, cbb.get(), &body, SSL3_MT_CLIENT_HELLO) ||
!CBB_init(encoded_cbb.get(), 256) ||
!ssl_write_client_hello_without_extensions(hs, &body,
ssl_client_hello_inner,
/*empty_session_id=*/false) ||
!ssl_write_client_hello_without_extensions(hs, encoded_cbb.get(),
ssl_client_hello_inner,
/*empty_session_id=*/true) ||
!ssl_add_clienthello_tlsext(hs, &body, encoded_cbb.get(),
&needs_psk_binder, ssl_client_hello_inner,
CBB_len(&body)) ||
!ssl->method->finish_message(ssl, cbb.get(), &hello_inner)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
if (needs_psk_binder) {
size_t binder_len;
if (!tls13_write_psk_binder(hs, hs->inner_transcript, MakeSpan(hello_inner),
&binder_len)) {
return false;
}
// Also update the EncodedClientHelloInner.
auto encoded_binder =
MakeSpan(const_cast<uint8_t *>(CBB_data(encoded_cbb.get())),
CBB_len(encoded_cbb.get()))
.last(binder_len);
auto hello_inner_binder = MakeConstSpan(hello_inner).last(binder_len);
OPENSSL_memcpy(encoded_binder.data(), hello_inner_binder.data(),
binder_len);
}
ssl_do_msg_callback(ssl, /*is_write=*/1, SSL3_RT_CLIENT_HELLO_INNER,
hello_inner);
if (!hs->inner_transcript.Update(hello_inner)) {
return false;
}
// Pad the EncodedClientHelloInner. See draft-ietf-tls-esni-13, section 6.1.3.
size_t padding_len = 0;
size_t maximum_name_length = hs->selected_ech_config->maximum_name_length;
if (ssl->hostname) {
size_t hostname_len = strlen(ssl->hostname.get());
if (hostname_len <= maximum_name_length) {
padding_len = maximum_name_length - hostname_len;
}
} else {
// No SNI. Pad up to |maximum_name_length|, including server_name extension
// overhead.
padding_len = 9 + maximum_name_length;
}
// Pad the whole thing to a multiple of 32 bytes.
padding_len += 31 - ((CBB_len(encoded_cbb.get()) + padding_len - 1) % 32);
Array<uint8_t> encoded;
if (!CBB_add_zeros(encoded_cbb.get(), padding_len) ||
!CBBFinishArray(encoded_cbb.get(), &encoded)) {
return false;
}
// Encrypt |encoded|. See draft-ietf-tls-esni-13, section 6.1.1. First,
// assemble the extension with a placeholder value for ClientHelloOuterAAD.
// See draft-ietf-tls-esni-13, section 5.2.
const EVP_HPKE_KDF *kdf = EVP_HPKE_CTX_kdf(hs->ech_hpke_ctx.get());
const EVP_HPKE_AEAD *aead = EVP_HPKE_CTX_aead(hs->ech_hpke_ctx.get());
size_t payload_len = encoded.size() + aead_overhead(aead);
CBB enc_cbb, payload_cbb;
if (!CBB_init(cbb.get(), 256) ||
!CBB_add_u16(cbb.get(), EVP_HPKE_KDF_id(kdf)) ||
!CBB_add_u16(cbb.get(), EVP_HPKE_AEAD_id(aead)) ||
!CBB_add_u8(cbb.get(), hs->selected_ech_config->config_id) ||
!CBB_add_u16_length_prefixed(cbb.get(), &enc_cbb) ||
!CBB_add_bytes(&enc_cbb, enc.data(), enc.size()) ||
!CBB_add_u16_length_prefixed(cbb.get(), &payload_cbb) ||
!CBB_add_zeros(&payload_cbb, payload_len) ||
!CBBFinishArray(cbb.get(), &hs->ech_client_outer)) {
return false;
}
// Construct ClientHelloOuterAAD.
// TODO(https://crbug.com/boringssl/275): This ends up constructing the
// ClientHelloOuter twice. Instead, reuse |aad| for the ClientHello, now that
// draft-12 made the length prefixes match.
bssl::ScopedCBB aad;
if (!CBB_init(aad.get(), 256) ||
!ssl_write_client_hello_without_extensions(hs, aad.get(),
ssl_client_hello_outer,
/*empty_session_id=*/false) ||
!ssl_add_clienthello_tlsext(hs, aad.get(), /*out_encoded=*/nullptr,
&needs_psk_binder, ssl_client_hello_outer,
CBB_len(aad.get()))) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
// ClientHelloOuter may not require a PSK binder. Otherwise, we have a
// circular dependency.
assert(!needs_psk_binder);
// Replace the payload in |hs->ech_client_outer| with the encrypted value.
auto payload_span = MakeSpan(hs->ech_client_outer).last(payload_len);
#if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
// In fuzzer mode, the server expects a cleartext payload.
assert(payload_span.size() == encoded.size());
OPENSSL_memcpy(payload_span.data(), encoded.data(), encoded.size());
#else
if (!EVP_HPKE_CTX_seal(hs->ech_hpke_ctx.get(), payload_span.data(),
&payload_len, payload_span.size(), encoded.data(),
encoded.size(), CBB_data(aad.get()),
CBB_len(aad.get())) ||
payload_len != payload_span.size()) {
return false;
}
#endif // BORINGSSL_UNSAFE_FUZZER_MODE
return true;
}
BSSL_NAMESPACE_END
using namespace bssl;
void SSL_set_enable_ech_grease(SSL *ssl, int enable) {
if (!ssl->config) {
return;
}
ssl->config->ech_grease_enabled = !!enable;
}
int SSL_set1_ech_config_list(SSL *ssl, const uint8_t *ech_config_list,
size_t ech_config_list_len) {
if (!ssl->config) {
return 0;
}
auto span = MakeConstSpan(ech_config_list, ech_config_list_len);
if (!ssl_is_valid_ech_config_list(span)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_ECH_CONFIG_LIST);
return 0;
}
return ssl->config->client_ech_config_list.CopyFrom(span);
}
void SSL_get0_ech_name_override(const SSL *ssl, const char **out_name,
size_t *out_name_len) {
// When ECH is rejected, we use the public name. Note that, if
// |SSL_CTX_set_reverify_on_resume| is enabled, we reverify the certificate
// before the 0-RTT point. If also offering ECH, we verify as if
// ClientHelloInner was accepted and do not override. This works because, at
// this point, |ech_status| will be |ssl_ech_none|. See the
// ECH-Client-Reject-EarlyDataReject-OverrideNameOnRetry tests in runner.go.
const SSL_HANDSHAKE *hs = ssl->s3->hs.get();
if (!ssl->server && hs && ssl->s3->ech_status == ssl_ech_rejected) {
*out_name = reinterpret_cast<const char *>(
hs->selected_ech_config->public_name.data());
*out_name_len = hs->selected_ech_config->public_name.size();
} else {
*out_name = nullptr;
*out_name_len = 0;
}
}
void SSL_get0_ech_retry_configs(
const SSL *ssl, const uint8_t **out_retry_configs,
size_t *out_retry_configs_len) {
const SSL_HANDSHAKE *hs = ssl->s3->hs.get();
if (!hs || !hs->ech_authenticated_reject) {
// It is an error to call this function except in response to
// |SSL_R_ECH_REJECTED|. Returning an empty string risks the caller
// mistakenly believing the server has disabled ECH. Instead, return a
// non-empty ECHConfigList with a syntax error, so the subsequent
// |SSL_set1_ech_config_list| call will fail.
assert(0);
static const uint8_t kPlaceholder[] = {
kECHConfigVersion >> 8, kECHConfigVersion & 0xff, 0xff, 0xff, 0xff};
*out_retry_configs = kPlaceholder;
*out_retry_configs_len = sizeof(kPlaceholder);
return;
}
*out_retry_configs = hs->ech_retry_configs.data();
*out_retry_configs_len = hs->ech_retry_configs.size();
}
int SSL_marshal_ech_config(uint8_t **out, size_t *out_len, uint8_t config_id,
const EVP_HPKE_KEY *key, const char *public_name,
size_t max_name_len) {
Span<const uint8_t> public_name_u8 = MakeConstSpan(
reinterpret_cast<const uint8_t *>(public_name), strlen(public_name));
if (!ssl_is_valid_ech_public_name(public_name_u8)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_ECH_PUBLIC_NAME);
return 0;
}
// The maximum name length is encoded in one byte.
if (max_name_len > 0xff) {
OPENSSL_PUT_ERROR(SSL, SSL_R_BAD_LENGTH);
return 0;
}
// See draft-ietf-tls-esni-13, section 4.
ScopedCBB cbb;
CBB contents, child;
uint8_t *public_key;
size_t public_key_len;
if (!CBB_init(cbb.get(), 128) || //
!CBB_add_u16(cbb.get(), kECHConfigVersion) ||
!CBB_add_u16_length_prefixed(cbb.get(), &contents) ||
!CBB_add_u8(&contents, config_id) ||
!CBB_add_u16(&contents, EVP_HPKE_KEM_id(EVP_HPKE_KEY_kem(key))) ||
!CBB_add_u16_length_prefixed(&contents, &child) ||
!CBB_reserve(&child, &public_key, EVP_HPKE_MAX_PUBLIC_KEY_LENGTH) ||
!EVP_HPKE_KEY_public_key(key, public_key, &public_key_len,
EVP_HPKE_MAX_PUBLIC_KEY_LENGTH) ||
!CBB_did_write(&child, public_key_len) ||
!CBB_add_u16_length_prefixed(&contents, &child) ||
// Write a default cipher suite configuration.
!CBB_add_u16(&child, EVP_HPKE_HKDF_SHA256) ||
!CBB_add_u16(&child, EVP_HPKE_AES_128_GCM) ||
!CBB_add_u16(&child, EVP_HPKE_HKDF_SHA256) ||
!CBB_add_u16(&child, EVP_HPKE_CHACHA20_POLY1305) ||
!CBB_add_u8(&contents, max_name_len) ||
!CBB_add_u8_length_prefixed(&contents, &child) ||
!CBB_add_bytes(&child, public_name_u8.data(), public_name_u8.size()) ||
// TODO(https://crbug.com/boringssl/275): Reserve some GREASE extensions
// and include some.
!CBB_add_u16(&contents, 0 /* no extensions */) ||
!CBB_finish(cbb.get(), out, out_len)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return 0;
}
return 1;
}
SSL_ECH_KEYS *SSL_ECH_KEYS_new() { return New<SSL_ECH_KEYS>(); }
void SSL_ECH_KEYS_up_ref(SSL_ECH_KEYS *keys) {
CRYPTO_refcount_inc(&keys->references);
}
void SSL_ECH_KEYS_free(SSL_ECH_KEYS *keys) {
if (keys == nullptr ||
!CRYPTO_refcount_dec_and_test_zero(&keys->references)) {
return;
}
keys->~ssl_ech_keys_st();
OPENSSL_free(keys);
}
int SSL_ECH_KEYS_add(SSL_ECH_KEYS *configs, int is_retry_config,
const uint8_t *ech_config, size_t ech_config_len,
const EVP_HPKE_KEY *key) {
UniquePtr<ECHServerConfig> parsed_config = MakeUnique<ECHServerConfig>();
if (!parsed_config) {
return 0;
}
if (!parsed_config->Init(MakeConstSpan(ech_config, ech_config_len), key,
!!is_retry_config)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return 0;
}
if (!configs->configs.Push(std::move(parsed_config))) {
return 0;
}
return 1;
}
int SSL_ECH_KEYS_has_duplicate_config_id(const SSL_ECH_KEYS *keys) {
bool seen[256] = {false};
for (const auto &config : keys->configs) {
if (seen[config->ech_config().config_id]) {
return 1;
}
seen[config->ech_config().config_id] = true;
}
return 0;
}
int SSL_ECH_KEYS_marshal_retry_configs(const SSL_ECH_KEYS *keys, uint8_t **out,
size_t *out_len) {
ScopedCBB cbb;
CBB child;
if (!CBB_init(cbb.get(), 128) ||
!CBB_add_u16_length_prefixed(cbb.get(), &child)) {
return false;
}
for (const auto &config : keys->configs) {
if (config->is_retry_config() &&
!CBB_add_bytes(&child, config->ech_config().raw.data(),
config->ech_config().raw.size())) {
return false;
}
}
return CBB_finish(cbb.get(), out, out_len);
}
int SSL_CTX_set1_ech_keys(SSL_CTX *ctx, SSL_ECH_KEYS *keys) {
bool has_retry_config = false;
for (const auto &config : keys->configs) {
if (config->is_retry_config()) {
has_retry_config = true;
break;
}
}
if (!has_retry_config) {
OPENSSL_PUT_ERROR(SSL, SSL_R_ECH_SERVER_WOULD_HAVE_NO_RETRY_CONFIGS);
return 0;
}
UniquePtr<SSL_ECH_KEYS> owned_keys = UpRef(keys);
MutexWriteLock lock(&ctx->lock);
ctx->ech_keys.swap(owned_keys);
return 1;
}
int SSL_ech_accepted(const SSL *ssl) {
if (SSL_in_early_data(ssl) && !ssl->server) {
// In the client early data state, we report properties as if the server
// accepted early data. The server can only accept early data with
// ClientHelloInner.
return ssl->s3->hs->selected_ech_config != nullptr;
}
return ssl->s3->ech_status == ssl_ech_accepted;
}