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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 <openssl/bytestring.h>
#include <openssl/curve25519.h>
#include <openssl/err.h>
#include <openssl/hkdf.h>
#include <openssl/hpke.h>
#include "internal.h"
#if defined(OPENSSL_MSAN)
#define NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
#else
#define NO_SANITIZE_MEMORY
#endif
BSSL_NAMESPACE_BEGIN
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;
}
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;
if (!ssl_client_hello_init(ssl, &client_hello_inner,
encoded_client_hello_inner)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
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;
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)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
// Sort the extensions in ClientHelloOuter, so ech_outer_extensions may be
// processed in O(n*log(n)) time, rather than O(n^2).
struct Extension {
uint16_t extension = 0;
Span<const uint8_t> body;
bool copied = false;
};
// MSan's libc interceptors do not handle |bsearch|. See b/182583130.
auto compare_extension = [](const void *a, const void *b)
NO_SANITIZE_MEMORY -> int {
const Extension *extension_a = reinterpret_cast<const Extension *>(a);
const Extension *extension_b = reinterpret_cast<const Extension *>(b);
if (extension_a->extension < extension_b->extension) {
return -1;
} else if (extension_a->extension > extension_b->extension) {
return 1;
}
return 0;
};
GrowableArray<Extension> sorted_extensions;
CBS unsorted_extensions(MakeConstSpan(client_hello_outer->extensions,
client_hello_outer->extensions_len));
while (CBS_len(&unsorted_extensions) > 0) {
Extension extension;
CBS extension_body;
if (!CBS_get_u16(&unsorted_extensions, &extension.extension) ||
!CBS_get_u16_length_prefixed(&unsorted_extensions, &extension_body)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
extension.body = extension_body;
if (!sorted_extensions.Push(extension)) {
return false;
}
}
qsort(sorted_extensions.data(), sorted_extensions.size(), sizeof(Extension),
compare_extension);
// Copy extensions from |client_hello_inner|, expanding ech_outer_extensions.
CBS inner_extensions(MakeConstSpan(client_hello_inner.extensions,
client_hello_inner.extensions_len));
while (CBS_len(&inner_extensions) > 0) {
uint16_t extension_id;
CBS extension_body;
if (!CBS_get_u16(&inner_extensions, &extension_id) ||
!CBS_get_u16_length_prefixed(&inner_extensions, &extension_body)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (extension_id != TLSEXT_TYPE_ech_outer_extensions) {
if (!CBB_add_u16(&extensions, extension_id) ||
!CBB_add_u16(&extensions, CBS_len(&extension_body)) ||
!CBB_add_bytes(&extensions, CBS_data(&extension_body),
CBS_len(&extension_body))) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
continue;
}
// Replace ech_outer_extensions with the corresponding outer extensions.
CBS outer_extensions;
if (!CBS_get_u8_length_prefixed(&extension_body, &outer_extensions) ||
CBS_len(&extension_body) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
while (CBS_len(&outer_extensions) > 0) {
uint16_t extension_needed;
if (!CBS_get_u16(&outer_extensions, &extension_needed)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (extension_needed == TLSEXT_TYPE_encrypted_client_hello) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// Find the referenced extension.
Extension key;
key.extension = extension_needed;
Extension *result = reinterpret_cast<Extension *>(
bsearch(&key, sorted_extensions.data(), sorted_extensions.size(),
sizeof(Extension), compare_extension));
if (result == nullptr) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// Extensions may be referenced at most once, to bound the result size.
if (result->copied) {
*out_alert = SSL_AD_ILLEGAL_PARAMETER;
OPENSSL_PUT_ERROR(SSL, SSL_R_DUPLICATE_EXTENSION);
return false;
}
result->copied = true;
if (!CBB_add_u16(&extensions, extension_needed) ||
!CBB_add_u16(&extensions, result->body.size()) ||
!CBB_add_bytes(&extensions, result->body.data(),
result->body.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
}
}
if (!CBB_flush(&body)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return false;
}
// See https://github.com/tlswg/draft-ietf-tls-esni/pull/411
CBS extension;
if (!ssl_client_hello_init(ssl, &client_hello_inner,
MakeConstSpan(CBB_data(&body), CBB_len(&body))) ||
!ssl_client_hello_get_extension(&client_hello_inner, &extension,
TLSEXT_TYPE_ech_is_inner) ||
CBS_len(&extension) != 0 ||
ssl_client_hello_get_extension(&client_hello_inner, &extension,
TLSEXT_TYPE_encrypted_client_hello) ||
!ssl_client_hello_get_extension(&client_hello_inner, &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;
}
}
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(
EVP_HPKE_CTX *hpke_ctx, Array<uint8_t> *out_encoded_client_hello_inner,
bool *out_is_decrypt_error, const SSL_CLIENT_HELLO *client_hello_outer,
uint16_t kdf_id, uint16_t aead_id, const uint8_t config_id,
Span<const uint8_t> enc, Span<const uint8_t> payload) {
*out_is_decrypt_error = false;
// Compute the ClientHello portion of the ClientHelloOuterAAD value. See
// draft-ietf-tls-esni-10, section 5.2.
ScopedCBB ch_outer_aad_cbb;
CBB enc_cbb, outer_hello_cbb, extensions_cbb;
if (!CBB_init(ch_outer_aad_cbb.get(), 0) ||
!CBB_add_u16(ch_outer_aad_cbb.get(), kdf_id) ||
!CBB_add_u16(ch_outer_aad_cbb.get(), aead_id) ||
!CBB_add_u8(ch_outer_aad_cbb.get(), config_id) ||
!CBB_add_u16_length_prefixed(ch_outer_aad_cbb.get(), &enc_cbb) ||
!CBB_add_bytes(&enc_cbb, enc.data(), enc.size()) ||
!CBB_add_u24_length_prefixed(ch_outer_aad_cbb.get(), &outer_hello_cbb) ||
!ssl_client_hello_write_without_extensions(client_hello_outer,
&outer_hello_cbb) ||
!CBB_add_u16_length_prefixed(&outer_hello_cbb, &extensions_cbb)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
CBS extensions(MakeConstSpan(client_hello_outer->extensions,
client_hello_outer->extensions_len));
while (CBS_len(&extensions) > 0) {
uint16_t extension_id;
CBS extension_body;
if (!CBS_get_u16(&extensions, &extension_id) ||
!CBS_get_u16_length_prefixed(&extensions, &extension_body)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
if (extension_id == TLSEXT_TYPE_encrypted_client_hello) {
continue;
}
if (!CBB_add_u16(&extensions_cbb, extension_id) ||
!CBB_add_u16(&extensions_cbb, CBS_len(&extension_body)) ||
!CBB_add_bytes(&extensions_cbb, CBS_data(&extension_body),
CBS_len(&extension_body))) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
}
if (!CBB_flush(ch_outer_aad_cbb.get())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
#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_is_decrypt_error = true;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED);
return false;
}
if (!out_encoded_client_hello_inner->CopyFrom(payload)) {
return false;
}
#else
// Attempt to decrypt into |out_encoded_client_hello_inner|.
if (!out_encoded_client_hello_inner->Init(payload.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
size_t encoded_client_hello_inner_len;
if (!EVP_HPKE_CTX_open(hpke_ctx, out_encoded_client_hello_inner->data(),
&encoded_client_hello_inner_len,
out_encoded_client_hello_inner->size(), payload.data(),
payload.size(), CBB_data(ch_outer_aad_cbb.get()),
CBB_len(ch_outer_aad_cbb.get()))) {
*out_is_decrypt_error = true;
OPENSSL_PUT_ERROR(SSL, SSL_R_DECRYPTION_FAILED);
return false;
}
out_encoded_client_hello_inner->Shrink(encoded_client_hello_inner_len);
#endif
return true;
}
bool ECHServerConfig::Init(Span<const uint8_t> ech_config,
const EVP_HPKE_KEY *key, bool is_retry_config) {
assert(!initialized_);
is_retry_config_ = is_retry_config;
if (!ech_config_.CopyFrom(ech_config)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return false;
}
// Read from |ech_config_| so we can save Spans with the same lifetime as |this|.
CBS reader(ech_config_);
uint16_t version;
if (!CBS_get_u16(&reader, &version)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// 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.
if (version != TLSEXT_TYPE_encrypted_client_hello) {
OPENSSL_PUT_ERROR(SSL, SSL_R_UNSUPPORTED_ECH_SERVER_CONFIG);
return false;
}
CBS ech_config_contents, public_name, public_key, cipher_suites, extensions;
uint16_t kem_id, max_name_len;
if (!CBS_get_u16_length_prefixed(&reader, &ech_config_contents) ||
!CBS_get_u8(&ech_config_contents, &config_id_) ||
!CBS_get_u16(&ech_config_contents, &kem_id) ||
!CBS_get_u16_length_prefixed(&ech_config_contents, &public_key) ||
CBS_len(&public_key) == 0 ||
!CBS_get_u16_length_prefixed(&ech_config_contents, &cipher_suites) ||
CBS_len(&cipher_suites) == 0 ||
!CBS_get_u16(&ech_config_contents, &max_name_len) ||
!CBS_get_u16_length_prefixed(&ech_config_contents, &public_name) ||
CBS_len(&public_name) == 0 ||
!CBS_get_u16_length_prefixed(&ech_config_contents, &extensions) ||
CBS_len(&ech_config_contents) != 0 || //
CBS_len(&reader) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return false;
}
// We do not support any ECHConfig extensions, so |extensions| must be empty.
if (CBS_len(&extensions) != 0) {
OPENSSL_PUT_ERROR(SSL, SSL_R_ECH_SERVER_CONFIG_UNSUPPORTED_EXTENSION);
return false;
}
cipher_suites_ = 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 (kem_id != EVP_HPKE_KEM_id(EVP_HPKE_KEY_kem(key)) ||
MakeConstSpan(expected_public_key, expected_public_key_len) !=
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;
}
initialized_ = true;
return true;
}
bool ECHServerConfig::SetupContext(EVP_HPKE_CTX *ctx, uint16_t kdf_id,
uint16_t aead_id,
Span<const uint8_t> enc) const {
assert(initialized_);
// Check the cipher suite is supported by this ECHServerConfig.
CBS cbs(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_.size()) ||
!CBB_add_bytes(info_cbb.get(), kInfoLabel,
sizeof(kInfoLabel) /* includes trailing NUL */) ||
!CBB_add_bytes(info_cbb.get(), ech_config_.data(), ech_config_.size())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
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()));
}
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;
}
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))) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
return 0;
}
return 1;
}
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) {
return ssl->s3->ech_accept;
}