Botan 3.1.1
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/tls_handshake_hash.h>
17#include <botan/internal/tls_handshake_io.h>
18#include <botan/internal/tls_handshake_state.h>
19#include <botan/internal/tls_reader.h>
20
21#include <botan/ecdh.h>
22#include <botan/rsa.h>
23
24namespace Botan::TLS {
25
26/*
27* Create a new Client Key Exchange message
28*/
30 Handshake_State& state,
31 const Policy& policy,
33 const Public_Key* server_public_key,
34 std::string_view hostname,
36 const Kex_Algo kex_algo = state.ciphersuite().kex_method();
37
38 if(kex_algo == Kex_Algo::PSK) {
39 std::string identity_hint;
40
41 if(state.server_kex()) {
42 TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
43 identity_hint = reader.get_string(2, 0, 65535);
44 }
45
46 const std::string psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
47
48 append_tls_length_value(m_key_material, psk_identity, 2);
49
50 SymmetricKey psk = creds.psk("tls-client", std::string(hostname), psk_identity);
51
52 std::vector<uint8_t> zeros(psk.length());
53
54 append_tls_length_value(m_pre_master, zeros, 2);
55 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
56 } else if(state.server_kex()) {
57 TLS_Data_Reader reader("ClientKeyExchange", state.server_kex()->params());
58
59 SymmetricKey psk;
60
61 if(kex_algo == Kex_Algo::ECDHE_PSK) {
62 std::string identity_hint = reader.get_string(2, 0, 65535);
63
64 const std::string psk_identity = creds.psk_identity("tls-client", std::string(hostname), identity_hint);
65
66 append_tls_length_value(m_key_material, psk_identity, 2);
67
68 psk = creds.psk("tls-client", std::string(hostname), psk_identity);
69 }
70
71 if(kex_algo == Kex_Algo::DH) {
72 const auto modulus = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
73 const auto generator = BigInt::decode(reader.get_range<uint8_t>(2, 1, 65535));
74 const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(2, 1, 65535);
75
76 if(reader.remaining_bytes()) {
77 throw Decoding_Error("Bad params size for DH key exchange");
78 }
79
80 DL_Group group(modulus, generator);
81
82 if(!group.verify_group(rng, false)) {
83 throw TLS_Exception(Alert::InsufficientSecurity, "DH group validation failed");
84 }
85
86 const auto private_key = state.callbacks().tls_generate_ephemeral_key(group, rng);
87 auto shared_secret = CT::strip_leading_zeros(
88 state.callbacks().tls_ephemeral_key_agreement(group, *private_key, peer_public_value, rng, policy));
89
90 if(kex_algo == Kex_Algo::DH) {
91 m_pre_master = std::move(shared_secret);
92 } else {
93 append_tls_length_value(m_pre_master, shared_secret, 2);
94 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
95 }
96
97 append_tls_length_value(m_key_material, private_key->public_value(), 2);
98 } else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
99 const uint8_t curve_type = reader.get_byte();
100 if(curve_type != 3) {
101 throw Decoding_Error("Server sent non-named ECC curve");
102 }
103
104 const Group_Params curve_id = static_cast<Group_Params>(reader.get_uint16_t());
105 const std::vector<uint8_t> peer_public_value = reader.get_range<uint8_t>(1, 1, 255);
106
107 if(policy.choose_key_exchange_group({curve_id}, {}) != curve_id) {
108 throw TLS_Exception(Alert::HandshakeFailure, "Server sent ECC curve prohibited by policy");
109 }
110
111 const auto private_key = state.callbacks().tls_generate_ephemeral_key(curve_id, rng);
112 auto shared_secret =
113 state.callbacks().tls_ephemeral_key_agreement(curve_id, *private_key, peer_public_value, rng, policy);
114
115 // RFC 8422 - 5.11.
116 // With X25519 and X448, a receiving party MUST check whether the
117 // computed premaster secret is the all-zero value and abort the
118 // handshake if so, as described in Section 6 of [RFC7748].
119 if(curve_id == Group_Params::X25519 && CT::all_zeros(shared_secret.data(), shared_secret.size()).is_set()) {
120 throw TLS_Exception(Alert::DecryptError, "Bad X25519 key exchange");
121 }
122
123 if(kex_algo == Kex_Algo::ECDH) {
124 m_pre_master = std::move(shared_secret);
125 } else {
126 append_tls_length_value(m_pre_master, shared_secret, 2);
127 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
128 }
129
130 if(is_ecdh(curve_id)) {
131 auto ecdh_key = dynamic_cast<ECDH_PublicKey*>(private_key.get());
132 if(!ecdh_key) {
133 throw TLS_Exception(Alert::InternalError, "Application did not provide a ECDH_PublicKey");
134 }
135 append_tls_length_value(m_key_material,
136 ecdh_key->public_value(state.server_hello()->prefers_compressed_ec_points()
139 1);
140 } else {
141 append_tls_length_value(m_key_material, private_key->public_value(), 1);
142 }
143 } else {
144 throw Internal_Error("Client_Key_Exchange: Unknown key exchange method was negotiated");
145 }
146
147 reader.assert_done();
148 } else {
149 // No server key exchange msg better mean RSA kex + RSA key in cert
150
151 if(kex_algo != Kex_Algo::STATIC_RSA) {
152 throw Unexpected_Message("No server kex message, but negotiated a key exchange that required it");
153 }
154
155 if(!server_public_key) {
156 throw Internal_Error("No server public key for RSA exchange");
157 }
158
159 if(auto rsa_pub = dynamic_cast<const RSA_PublicKey*>(server_public_key)) {
160 const Protocol_Version offered_version = state.client_hello()->legacy_version();
161
162 rng.random_vec(m_pre_master, 48);
163 m_pre_master[0] = offered_version.major_version();
164 m_pre_master[1] = offered_version.minor_version();
165
166 PK_Encryptor_EME encryptor(*rsa_pub, rng, "PKCS1v15");
167
168 const std::vector<uint8_t> encrypted_key = encryptor.encrypt(m_pre_master, rng);
169
170 append_tls_length_value(m_key_material, encrypted_key, 2);
171 } else {
172 throw TLS_Exception(Alert::HandshakeFailure,
173 "Expected a RSA key in server cert but got " + server_public_key->algo_name());
174 }
175 }
176
177 state.hash().update(io.send(*this));
178}
179
180/*
181* Read a Client Key Exchange message
182*/
183Client_Key_Exchange::Client_Key_Exchange(const std::vector<uint8_t>& contents,
184 const Handshake_State& state,
185 const Private_Key* server_rsa_kex_key,
186 Credentials_Manager& creds,
187 const Policy& policy,
189 const Kex_Algo kex_algo = state.ciphersuite().kex_method();
190
191 if(kex_algo == Kex_Algo::STATIC_RSA) {
192 BOTAN_ASSERT(state.server_certs() && !state.server_certs()->cert_chain().empty(),
193 "RSA key exchange negotiated so server sent a certificate");
194
195 if(!server_rsa_kex_key) {
196 throw Internal_Error("Expected RSA kex but no server kex key set");
197 }
198
199 if(server_rsa_kex_key->algo_name() != "RSA") {
200 throw Internal_Error("Expected RSA key but got " + server_rsa_kex_key->algo_name());
201 }
202
203 TLS_Data_Reader reader("ClientKeyExchange", contents);
204 const std::vector<uint8_t> encrypted_pre_master = reader.get_range<uint8_t>(2, 0, 65535);
205 reader.assert_done();
206
207 PK_Decryptor_EME decryptor(*server_rsa_kex_key, rng, "PKCS1v15");
208
209 const uint8_t client_major = state.client_hello()->legacy_version().major_version();
210 const uint8_t client_minor = state.client_hello()->legacy_version().minor_version();
211
212 /*
213 * PK_Decryptor::decrypt_or_random will return a random value if
214 * either the length does not match the expected value or if the
215 * version number embedded in the PMS does not match the one sent
216 * in the client hello.
217 */
218 const size_t expected_plaintext_size = 48;
219 const size_t expected_content_size = 2;
220 const uint8_t expected_content_bytes[expected_content_size] = {client_major, client_minor};
221 const uint8_t expected_content_pos[expected_content_size] = {0, 1};
222
223 m_pre_master = decryptor.decrypt_or_random(encrypted_pre_master.data(),
224 encrypted_pre_master.size(),
225 expected_plaintext_size,
226 rng,
227 expected_content_bytes,
228 expected_content_pos,
229 expected_content_size);
230 } else {
231 TLS_Data_Reader reader("ClientKeyExchange", contents);
232
233 SymmetricKey psk;
234
235 if(key_exchange_is_psk(kex_algo)) {
236 const std::string psk_identity = reader.get_string(2, 0, 65535);
237
238 psk = creds.psk("tls-server", state.client_hello()->sni_hostname(), psk_identity);
239
240 if(psk.length() == 0) {
241 if(policy.hide_unknown_users()) {
242 psk = SymmetricKey(rng, 16);
243 } else {
244 throw TLS_Exception(Alert::UnknownPSKIdentity, "No PSK for identifier " + psk_identity);
245 }
246 }
247 }
248
249 if(kex_algo == Kex_Algo::PSK) {
250 std::vector<uint8_t> zeros(psk.length());
251 append_tls_length_value(m_pre_master, zeros, 2);
252 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
253 } else if(kex_algo == Kex_Algo::DH || kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
254 const PK_Key_Agreement_Key& ka_key = state.server_kex()->server_kex_key();
255
256 const std::vector<uint8_t> client_pubkey = (ka_key.algo_name() == "DH")
257 ? reader.get_range<uint8_t>(2, 0, 65535)
258 : reader.get_range<uint8_t>(1, 1, 255);
259
260 const auto shared_group = state.server_kex()->shared_group();
261 BOTAN_STATE_CHECK(shared_group && shared_group.value() != Group_Params::NONE);
262
263 try {
264 auto shared_secret =
265 state.callbacks().tls_ephemeral_key_agreement(shared_group.value(), ka_key, client_pubkey, rng, policy);
266
267 if(ka_key.algo_name() == "DH") {
268 shared_secret = CT::strip_leading_zeros(shared_secret);
269 }
270
271 if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
272 // RFC 8422 - 5.11.
273 // With X25519 and X448, a receiving party MUST check whether the
274 // computed premaster secret is the all-zero value and abort the
275 // handshake if so, as described in Section 6 of [RFC7748].
276 BOTAN_ASSERT_NOMSG(state.server_kex()->params().size() >= 3);
277 Group_Params group = static_cast<Group_Params>(state.server_kex()->params().at(2));
278 if(group == Group_Params::X25519 && CT::all_zeros(shared_secret.data(), shared_secret.size()).is_set()) {
279 throw TLS_Exception(Alert::DecryptError, "Bad X25519 key exchange");
280 }
281 }
282
283 if(kex_algo == Kex_Algo::ECDHE_PSK) {
284 append_tls_length_value(m_pre_master, shared_secret, 2);
285 append_tls_length_value(m_pre_master, psk.bits_of(), 2);
286 } else {
287 m_pre_master = shared_secret;
288 }
289 } catch(Invalid_Argument& e) {
290 throw TLS_Exception(Alert::IllegalParameter, e.what());
291 } catch(TLS_Exception& e) {
292 // NOLINTNEXTLINE(cert-err60-cpp)
293 throw e;
294 } catch(std::exception&) {
295 /*
296 * Something failed in the DH/ECDH computation. To avoid possible
297 * attacks which are based on triggering and detecting some edge
298 * failure condition, randomize the pre-master output and carry on,
299 * allowing the protocol to fail later in the finished checks.
300 */
301 rng.random_vec(m_pre_master, ka_key.public_value().size());
302 }
303
304 reader.assert_done();
305 } else {
306 throw Internal_Error("Client_Key_Exchange: Unknown key exchange negotiated");
307 }
308 }
309}
310
311} // 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:760
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:78
virtual std::vector< uint8_t > public_value() const =0
void random_vec(std::span< uint8_t > v)
Definition: rng.h:180
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)
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
Definition: tls_policy.cpp:342
virtual Group_Params choose_key_exchange_group(const std::vector< Group_Params > &supported_by_peer, const std::vector< Group_Params > &offered_by_peer) const
Definition: tls_policy.cpp:118
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:38
CT::Mask< T > all_zeros(const T elem[], size_t len)
Definition: ct_utils.h:320
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:176
constexpr bool is_ecdh(const Group_Params group)
Definition: tls_algos.h:106
bool key_exchange_is_psk(Kex_Algo m)
Definition: tls_algos.h:140
OctetString SymmetricKey
Definition: symkey.h:141