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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"
#if defined(OPENSSL_MSAN)
#define NO_SANITIZE_MEMORY __attribute__((no_sanitize("memory")))
#else
#define NO_SANITIZE_MEMORY
#endif
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;
}
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 aad;
CBB enc_cbb, outer_hello_cbb, extensions_cbb;
if (!CBB_init(aad.get(), 256) ||
!CBB_add_u16(aad.get(), kdf_id) ||
!CBB_add_u16(aad.get(), aead_id) ||
!CBB_add_u8(aad.get(), config_id) ||
!CBB_add_u16_length_prefixed(aad.get(), &enc_cbb) ||
!CBB_add_bytes(&enc_cbb, enc.data(), enc.size()) ||
!CBB_add_u24_length_prefixed(aad.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(aad.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(aad.get()),
CBB_len(aad.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;
}
static bool parse_ipv4_number(Span<const uint8_t> in, uint32_t *out) {
// See https://url.spec.whatwg.org/#ipv4-number-parser.
uint32_t base = 10;
if (in.size() >= 2 && in[0] == '0' && (in[1] == 'x' || in[1] == 'X')) {
in = in.subspan(2);
base = 16;
} else if (in.size() >= 1 && in[0] == '0') {
in = in.subspan(1);
base = 8;
}
*out = 0;
for (uint8_t c : in) {
uint32_t d;
if ('0' <= c && c <= '9') {
d = c - '0';
} else if ('a' <= c && c <= 'f') {
d = c - 'a' + 10;
} else if ('A' <= c && c <= 'F') {
d = c - 'A' + 10;
} else {
return false;
}
if (d >= base ||
*out > UINT32_MAX / base) {
return false;
}
*out *= base;
if (*out > UINT32_MAX - d) {
return false;
}
*out += d;
}
return true;
}
static bool is_ipv4_address(Span<const uint8_t> in) {
// See https://url.spec.whatwg.org/#concept-ipv4-parser
uint32_t numbers[4];
size_t num_numbers = 0;
while (!in.empty()) {
if (num_numbers == 4) {
// Too many components.
return false;
}
// Find the next dot-separated component.
auto dot = std::find(in.begin(), in.end(), '.');
if (dot == in.begin()) {
// Empty components are not allowed.
return false;
}
Span<const uint8_t> component;
if (dot == in.end()) {
component = in;
in = Span<const uint8_t>();
} else {
component = in.subspan(0, dot - in.begin());
in = in.subspan(dot - in.begin() + 1); // Skip the dot.
}
if (!parse_ipv4_number(component, &numbers[num_numbers])) {
return false;
}
num_numbers++;
}
if (num_numbers == 0) {
return false;
}
for (size_t i = 0; i < num_numbers - 1; i++) {
if (numbers[i] > 255) {
return false;
}
}
return num_numbers == 1 ||
numbers[num_numbers - 1] < 1u << (8 * (5 - num_numbers));
}
bool ssl_is_valid_ech_public_name(Span<const uint8_t> public_name) {
// See draft-ietf-tls-esni-11, 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 copy = public_name;
if (copy.empty()) {
return false;
}
while (!copy.empty()) {
// Find the next dot-separated component.
auto dot = std::find(copy.begin(), copy.end(), '.');
Span<const uint8_t> component;
if (dot == copy.end()) {
component = copy;
copy = Span<const uint8_t>();
} else {
component = copy.subspan(0, dot - copy.begin());
copy = copy.subspan(dot - copy.begin() + 1); // Skip the dot.
if (copy.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 (!('a' <= c && c <= 'z') && !('A' <= c && c <= 'Z') &&
!('0' <= c && c <= '9') && c != '-') {
return false;
}
}
}
return !is_ipv4_address(public_name);
}
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_u16(&contents, &out->maximum_name_length) ||
!CBS_get_u16_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())) {
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()));
}
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 = EVP_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)) {
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())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
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
}
static size_t compute_extension_length(const EVP_HPKE_AEAD *aead,
size_t enc_len, size_t in_len) {
size_t ret = 4; // HpkeSymmetricCipherSuite cipher_suite
ret++; // uint8 config_id
ret += 2 + enc_len; // opaque enc<1..2^16-1>
ret += 2 + in_len + aead_overhead(aead); // opaque payload<1..2^16-1>
return ret;
}
// 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 EVP_HPKE_AEAD *aead = EVP_has_aes_hardware()
? 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
// 4 ech_is_inner
// 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.
//
// TODO(https://crbug.com/boringssl/275): If the padding scheme changes to
// also round the entire payload, adjust this to match. See
// https://github.com/tlswg/draft-ietf-tls-esni/issues/433
const size_t overhead = aead_overhead(aead);
const size_t in_len = random_size(128, 196);
const size_t extension_len =
compute_extension_length(aead, sizeof(enc), in_len);
bssl::ScopedCBB cbb;
CBB enc_cbb, payload_cbb;
uint8_t *payload;
if (!CBB_init(cbb.get(), extension_len) ||
!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, in_len + overhead) ||
!RAND_bytes(payload, in_len + overhead) ||
!CBBFinishArray(cbb.get(), &hs->ech_client_bytes)) {
return false;
}
assert(hs->ech_client_bytes.size() == extension_len);
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-10, sections 5.1 and 6.1.
ScopedCBB cbb, encoded_cbb;
CBB body;
bool needs_psk_binder;
Array<uint8_t> hello_inner, encoded;
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),
/*omit_ech_len=*/0) ||
!ssl->method->finish_message(ssl, cbb.get(), &hello_inner) ||
!CBBFinishArray(encoded_cbb.get(), &encoded)) {
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(encoded).last(binder_len);
auto hello_inner_binder = MakeConstSpan(hello_inner).last(binder_len);
OPENSSL_memcpy(encoded_binder.data(), hello_inner_binder.data(),
binder_len);
}
if (!hs->inner_transcript.Update(hello_inner)) {
return false;
}
// Construct ClientHelloOuterAAD. See draft-ietf-tls-esni-10, section 5.2.
// TODO(https://crbug.com/boringssl/275): This ends up constructing the
// ClientHelloOuter twice. Revisit this in the next draft, which uses a more
// forgiving construction.
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());
const size_t extension_len =
compute_extension_length(aead, enc.size(), encoded.size());
bssl::ScopedCBB aad;
CBB outer_hello;
CBB enc_cbb;
if (!CBB_init(aad.get(), 256) ||
!CBB_add_u16(aad.get(), EVP_HPKE_KDF_id(kdf)) ||
!CBB_add_u16(aad.get(), EVP_HPKE_AEAD_id(aead)) ||
!CBB_add_u8(aad.get(), hs->selected_ech_config->config_id) ||
!CBB_add_u16_length_prefixed(aad.get(), &enc_cbb) ||
!CBB_add_bytes(&enc_cbb, enc.data(), enc.size()) ||
!CBB_add_u24_length_prefixed(aad.get(), &outer_hello) ||
!ssl_write_client_hello_without_extensions(hs, &outer_hello,
ssl_client_hello_outer,
/*empty_session_id=*/false) ||
!ssl_add_clienthello_tlsext(hs, &outer_hello, /*out_encoded=*/nullptr,
&needs_psk_binder, ssl_client_hello_outer,
CBB_len(&outer_hello),
/*omit_ech_len=*/4 + extension_len) ||
!CBB_flush(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);
CBB payload_cbb;
if (!CBB_init(cbb.get(), extension_len) ||
!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)) {
return false;
}
#if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
// In fuzzer mode, the server expects a cleartext payload.
if (!CBB_add_bytes(&payload_cbb, encoded.data(), encoded.size())) {
return false;
}
#else
uint8_t *payload;
size_t payload_len =
encoded.size() + EVP_AEAD_max_overhead(EVP_HPKE_AEAD_aead(aead));
if (!CBB_reserve(&payload_cbb, &payload, payload_len) ||
!EVP_HPKE_CTX_seal(hs->ech_hpke_ctx.get(), payload, &payload_len,
payload_len, encoded.data(), encoded.size(),
CBB_data(aad.get()), CBB_len(aad.get())) ||
!CBB_did_write(&payload_cbb, payload_len)) {
return false;
}
#endif // BORINGSSL_UNSAFE_FUZZER_MODE
if (!CBBFinishArray(cbb.get(), &hs->ech_client_bytes)) {
return false;
}
// The |aad| calculation relies on |extension_length| being correct.
assert(hs->ech_client_bytes.size() == extension_len);
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;
}
// See draft-ietf-tls-esni-10, 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_u16(&contents, max_name_len) ||
!CBB_add_u16_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))) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
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)) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
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())) {
OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
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;
}