Botan 3.3.0
Crypto and TLS for C&
msg_client_kex.cpp
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1/*
2* Client Key Exchange Message
3* (C) 2004-2010,2016 Jack Lloyd
4* 2017 Harry Reimann, Rohde & Schwarz Cybersecurity
5*
6* Botan is released under the Simplified BSD License (see license.txt)
7*/
8
9#include <botan/tls_messages.h>
10
11#include <botan/rng.h>
12#include <botan/tls_extensions.h>
13
14#include <botan/credentials_manager.h>
15#include <botan/internal/ct_utils.h>
16#include <botan/internal/stl_util.h>
17#include <botan/internal/tls_handshake_hash.h>
18#include <botan/internal/tls_handshake_io.h>
19#include <botan/internal/tls_handshake_state.h>
20#include <botan/internal/tls_reader.h>
21
22#include <botan/ecdh.h>
23#include <botan/rsa.h>
24
25namespace Botan::TLS {
26
27/*
28* Create a new Client Key Exchange message
29*/
31 Handshake_State& state,
32 const Policy& policy,
34 const Public_Key* server_public_key,
35 std::string_view hostname,
37 const Kex_Algo kex_algo = state.ciphersuite().kex_method();
38
39 if(kex_algo == Kex_Algo::PSK) {
40 std::string identity_hint;
41
42 if(state.server_kex()) {
43 TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
44 identity_hint = reader.get_string(2, 0, 65535);
45 }
46
47 m_psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
48
49 append_tls_length_value(m_key_material, to_byte_vector(m_psk_identity.value()), 2);
50
51 SymmetricKey psk = creds.psk("tls-client", std::string(hostname), m_psk_identity.value());
52
53 std::vector<uint8_t> zeros(psk.length());
54
55 append_tls_length_value(m_pre_master, zeros, 2);
56 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
57 } else if(state.server_kex()) {
58 TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
59
60 SymmetricKey psk;
61
62 if(kex_algo == Kex_Algo::ECDHE_PSK) {
63 std::string identity_hint = reader.get_string(2, 0, 65535);
64
65 m_psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
66
67 append_tls_length_value(m_key_material, to_byte_vector(m_psk_identity.value()), 2);
68
69 psk = creds.psk("tls-client", std::string(hostname), m_psk_identity.value());
70 }
71
72 if(kex_algo == Kex_Algo::DH) {
73 const auto modulus = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
74 const auto generator = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
75 const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(2, 1, 65535);
76
77 if(reader.remaining_bytes()) {
78 throw Decoding_Error("Bad params size for DH key exchange");
79 }
80
81 DL_Group group(modulus, generator);
82
83 if(!group.verify_group(rng, false)) {
84 throw TLS_Exception(Alert::InsufficientSecurity, "DH group validation failed");
85 }
86
87 const auto private_key = state.callbacks().tls_generate_ephemeral_key(group, rng);
88 auto shared_secret = CT::strip_leading_zeros(
89 state.callbacks().tls_ephemeral_key_agreement(group, *private_key, peer_public_value, rng, policy));
90
91 if(kex_algo == Kex_Algo::DH) {
92 m_pre_master = std::move(shared_secret);
93 } else {
94 append_tls_length_value(m_pre_master, shared_secret, 2);
95 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
96 }
97
98 append_tls_length_value(m_key_material, private_key->public_value(), 2);
99 } else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
100 const uint8_t curve_type = reader.get_byte();
101 if(curve_type != 3) {
102 throw Decoding_Error("Server sent non-named ECC curve");
103 }
104
105 const Group_Params curve_id = static_cast<Group_Params>(reader.get_uint16_t());
106 const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(1, 1, 255);
107
108 if(!curve_id.is_ecdh_named_curve() && !curve_id.is_x25519()) {
109 throw TLS_Exception(Alert::HandshakeFailure,
110 "Server selected a group that is not compatible with the negotiated ciphersuite");
111 }
112
113 if(policy.choose_key_exchange_group({curve_id}, {}) != curve_id) {
114 throw TLS_Exception(Alert::HandshakeFailure, "Server sent ECC curve prohibited by policy");
115 }
116
117 const auto private_key = state.callbacks().tls_generate_ephemeral_key(curve_id, rng);
118 auto shared_secret =
119 state.callbacks().tls_ephemeral_key_agreement(curve_id, *private_key, peer_public_value, rng, policy);
120
121 // RFC 8422 - 5.11.
122 // With X25519 and X448, a receiving party MUST check whether the
123 // computed premaster secret is the all-zero value and abort the
124 // handshake if so, as described in Section 6 of [RFC7748].
125 if(curve_id == Group_Params::X25519 && CT::all_zeros(shared_secret.data(), shared_secret.size()).as_bool()) {
126 throw TLS_Exception(Alert::DecryptError, "Bad X25519 key exchange");
127 }
128
129 if(kex_algo == Kex_Algo::ECDH) {
130 m_pre_master = std::move(shared_secret);
131 } else {
132 append_tls_length_value(m_pre_master, shared_secret, 2);
133 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
134 }
135
136 if(curve_id.is_ecdh_named_curve()) {
137 auto ecdh_key = dynamic_cast<ECDH_PublicKey*>(private_key.get());
138 if(!ecdh_key) {
139 throw TLS_Exception(Alert::InternalError, "Application did not provide a ECDH_PublicKey");
140 }
141 append_tls_length_value(m_key_material,
142 ecdh_key->public_value(state.server_hello()->prefers_compressed_ec_points()
145 1);
146 } else {
147 append_tls_length_value(m_key_material, private_key->public_value(), 1);
148 }
149 } else {
150 throw Internal_Error("Client_Key_Exchange: Unknown key exchange method was negotiated");
151 }
152
153 reader.assert_done();
154 } else {
155 // No server key exchange msg better mean RSA kex + RSA key in cert
156
157 if(kex_algo != Kex_Algo::STATIC_RSA) {
158 throw Unexpected_Message("No server kex message, but negotiated a key exchange that required it");
159 }
160
161 if(!server_public_key) {
162 throw Internal_Error("No server public key for RSA exchange");
163 }
164
165 if(auto rsa_pub = dynamic_cast<const RSA_PublicKey*>(server_public_key)) {
166 const Protocol_Version offered_version = state.client_hello()->legacy_version();
167
168 rng.random_vec(m_pre_master, 48);
169 m_pre_master[0] = offered_version.major_version();
170 m_pre_master[1] = offered_version.minor_version();
171
172 PK_Encryptor_EME encryptor(*rsa_pub, rng, "PKCS1v15");
173
174 const std::vector<uint8_t> encrypted_key = encryptor.encrypt(m_pre_master, rng);
175
176 append_tls_length_value(m_key_material, encrypted_key, 2);
177 } else {
178 throw TLS_Exception(Alert::HandshakeFailure,
179 "Expected a RSA key in server cert but got " + server_public_key->algo_name());
180 }
181 }
182
183 state.hash().update(io.send(*this));
184}
185
186/*
187* Read a Client Key Exchange message
188*/
189Client_Key_Exchange::Client_Key_Exchange(const std::vector<uint8_t>& contents,
190 const Handshake_State& state,
191 const Private_Key* server_rsa_kex_key,
192 Credentials_Manager& creds,
193 const Policy& policy,
195 const Kex_Algo kex_algo = state.ciphersuite().kex_method();
196
197 if(kex_algo == Kex_Algo::STATIC_RSA) {
198 BOTAN_ASSERT(state.server_certs() && !state.server_certs()->cert_chain().empty(),
199 "RSA key exchange negotiated so server sent a certificate");
200
201 if(!server_rsa_kex_key) {
202 throw Internal_Error("Expected RSA kex but no server kex key set");
203 }
204
205 if(server_rsa_kex_key->algo_name() != "RSA") {
206 throw Internal_Error("Expected RSA key but got " + server_rsa_kex_key->algo_name());
207 }
208
209 TLS_Data_Reader reader("ClientKeyExchange", contents);
210 const std::vector<uint8_t> encrypted_pre_master = reader.get_range<uint8_t>(2, 0, 65535);
211 reader.assert_done();
212
213 PK_Decryptor_EME decryptor(*server_rsa_kex_key, rng, "PKCS1v15");
214
215 const uint8_t client_major = state.client_hello()->legacy_version().major_version();
216 const uint8_t client_minor = state.client_hello()->legacy_version().minor_version();
217
218 /*
219 * PK_Decryptor::decrypt_or_random will return a random value if
220 * either the length does not match the expected value or if the
221 * version number embedded in the PMS does not match the one sent
222 * in the client hello.
223 */
224 const size_t expected_plaintext_size = 48;
225 const size_t expected_content_size = 2;
226 const uint8_t expected_content_bytes[expected_content_size] = {client_major, client_minor};
227 const uint8_t expected_content_pos[expected_content_size] = {0, 1};
228
229 m_pre_master = decryptor.decrypt_or_random(encrypted_pre_master.data(),
230 encrypted_pre_master.size(),
231 expected_plaintext_size,
232 rng,
233 expected_content_bytes,
234 expected_content_pos,
235 expected_content_size);
236 } else {
237 TLS_Data_Reader reader("ClientKeyExchange", contents);
238
239 SymmetricKey psk;
240
241 if(key_exchange_is_psk(kex_algo)) {
242 m_psk_identity = reader.get_string(2, 0, 65535);
243
244 psk = creds.psk("tls-server", state.client_hello()->sni_hostname(), m_psk_identity.value());
245
246 if(psk.length() == 0) {
247 if(policy.hide_unknown_users()) {
248 psk = SymmetricKey(rng, 16);
249 } else {
250 throw TLS_Exception(Alert::UnknownPSKIdentity, "No PSK for identifier " + m_psk_identity.value());
251 }
252 }
253 }
254
255 if(kex_algo == Kex_Algo::PSK) {
256 std::vector<uint8_t> zeros(psk.length());
257 append_tls_length_value(m_pre_master, zeros, 2);
258 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
259 } else if(kex_algo == Kex_Algo::DH || kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
260 const PK_Key_Agreement_Key& ka_key = state.server_kex()->server_kex_key();
261
262 const std::vector<uint8_t> client_pubkey = (ka_key.algo_name() == "DH")
263 ? reader.get_range<uint8_t>(2, 0, 65535)
264 : reader.get_range<uint8_t>(1, 1, 255);
265
266 const auto shared_group = state.server_kex()->shared_group();
267 BOTAN_STATE_CHECK(shared_group && shared_group.value() != Group_Params::NONE);
268
269 try {
270 auto shared_secret =
271 state.callbacks().tls_ephemeral_key_agreement(shared_group.value(), ka_key, client_pubkey, rng, policy);
272
273 if(ka_key.algo_name() == "DH") {
274 shared_secret = CT::strip_leading_zeros(shared_secret);
275 }
276
277 if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
278 // RFC 8422 - 5.11.
279 // With X25519 and X448, a receiving party MUST check whether the
280 // computed premaster secret is the all-zero value and abort the
281 // handshake if so, as described in Section 6 of [RFC7748].
282 BOTAN_ASSERT_NOMSG(state.server_kex()->params().size() >= 3);
283 Group_Params group = static_cast<Group_Params>(state.server_kex()->params().at(2));
284 if(group == Group_Params::X25519 &&
285 CT::all_zeros(shared_secret.data(), shared_secret.size()).as_bool()) {
286 throw TLS_Exception(Alert::DecryptError, "Bad X25519 key exchange");
287 }
288 }
289
290 if(kex_algo == Kex_Algo::ECDHE_PSK) {
291 append_tls_length_value(m_pre_master, shared_secret, 2);
292 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
293 } else {
294 m_pre_master = shared_secret;
295 }
296 } catch(Invalid_Argument& e) {
297 throw TLS_Exception(Alert::IllegalParameter, e.what());
298 } catch(TLS_Exception& e) {
299 // NOLINTNEXTLINE(cert-err60-cpp)
300 throw e;
301 } catch(std::exception&) {
302 /*
303 * Something failed in the DH/ECDH computation. To avoid possible
304 * attacks which are based on triggering and detecting some edge
305 * failure condition, randomize the pre-master output and carry on,
306 * allowing the protocol to fail later in the finished checks.
307 */
308 rng.random_vec(m_pre_master, ka_key.public_value().size());
309 }
310
311 reader.assert_done();
312 } else {
313 throw Internal_Error("Client_Key_Exchange: Unknown key exchange negotiated");
314 }
315 }
316}
317
318} // namespace Botan::TLS
#define BOTAN_ASSERT_NOMSG(expr)
Definition assert.h:59
#define BOTAN_STATE_CHECK(expr)
Definition assert.h:41
#define BOTAN_ASSERT(expr, assertion_made)
Definition assert.h:50
virtual std::string algo_name() const =0
static BigInt decode(const uint8_t buf[], size_t length)
Definition bigint.h:772
virtual std::string psk_identity(const std::string &type, const std::string &context, const std::string &identity_hint)
virtual SymmetricKey psk(const std::string &type, const std::string &context, const std::string &identity)
bool verify_group(RandomNumberGenerator &rng, bool strong=true) const
Definition dl_group.cpp:373
const char * what() const noexcept override
Definition exceptn.h:93
secure_vector< uint8_t > bits_of() const
Definition symkey.h:36
size_t length() const
Definition symkey.h:27
secure_vector< uint8_t > decrypt_or_random(const uint8_t in[], size_t length, size_t expected_pt_len, RandomNumberGenerator &rng) const
Definition pubkey.cpp:79
std::vector< uint8_t > encrypt(const uint8_t in[], size_t length, RandomNumberGenerator &rng) const
Definition pubkey.h:37
virtual std::vector< uint8_t > public_value() const =0
void random_vec(std::span< uint8_t > v)
Definition rng.h:179
virtual secure_vector< uint8_t > tls_ephemeral_key_agreement(const std::variant< TLS::Group_Params, DL_Group > &group, const PK_Key_Agreement_Key &private_key, const std::vector< uint8_t > &public_value, RandomNumberGenerator &rng, const Policy &policy)
virtual std::unique_ptr< PK_Key_Agreement_Key > tls_generate_ephemeral_key(const std::variant< TLS::Group_Params, DL_Group > &group, RandomNumberGenerator &rng)
Kex_Algo kex_method() const
Client_Key_Exchange(Handshake_IO &io, Handshake_State &state, const Policy &policy, Credentials_Manager &creds, const Public_Key *server_public_key, std::string_view hostname, RandomNumberGenerator &rng)
constexpr bool is_ecdh_named_curve() const
Definition tls_algos.h:172
constexpr bool is_x25519() const
Definition tls_algos.h:170
void update(const uint8_t in[], size_t length)
virtual std::vector< uint8_t > send(const Handshake_Message &msg)=0
void server_certs(Certificate_12 *server_certs)
void server_hello(Server_Hello_12 *server_hello)
void server_kex(Server_Key_Exchange *server_kex)
const Ciphersuite & ciphersuite() const
void client_hello(Client_Hello_12 *client_hello)
virtual bool hide_unknown_users() const
virtual Group_Params choose_key_exchange_group(const std::vector< Group_Params > &supported_by_peer, const std::vector< Group_Params > &offered_by_peer) const
uint8_t major_version() const
Definition tls_version.h:78
uint8_t minor_version() const
Definition tls_version.h:83
std::string get_string(size_t len_bytes, size_t min_bytes, size_t max_bytes)
Definition tls_reader.h:118
std::vector< T > get_range(size_t len_bytes, size_t min_elems, size_t max_elems)
Definition tls_reader.h:105
size_t remaining_bytes() const
Definition tls_reader.h:37
CT::Mask< T > all_zeros(const T elem[], size_t len)
Definition ct_utils.h:326
secure_vector< uint8_t > strip_leading_zeros(const uint8_t in[], size_t length)
Definition ct_utils.cpp:84
void append_tls_length_value(std::vector< uint8_t, Alloc > &buf, const T *vals, size_t vals_size, size_t tag_size)
Definition tls_reader.h:180
bool key_exchange_is_psk(Kex_Algo m)
Definition tls_algos.h:253
T to_byte_vector(std::string_view s)
Definition stl_util.h:29
OctetString SymmetricKey
Definition symkey.h:141