5111374265

Committed 29 May 2023 11:19AM UTC coverage: 92.227% (+0.5%) from 91.723%

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Next release will be 3.1.0. Update release notes

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90.38

/src/lib/tls/tls12/msg_server_kex.cpp

/*
* Server Key Exchange Message
* (C) 2004-2010,2012,2015,2016 Jack Lloyd
*     2017 Harry Reimann, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/tls_messages.h>

#include <botan/credentials_manager.h>
#include <botan/pubkey.h>
#include <botan/tls_extensions.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/tls_handshake_io.h>
#include <botan/internal/tls_handshake_state.h>
#include <botan/internal/tls_reader.h>

#include <botan/dh.h>
#include <botan/dl_group.h>
#include <botan/ecdh.h>

#if defined(BOTAN_HAS_CURVE_25519)
   #include <botan/curve25519.h>
#endif

namespace Botan::TLS {

/**
* Create a new Server Key Exchange message
*/
Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,
                                         Handshake_State& state,
                                         const Policy& policy,
                                         Credentials_Manager& creds,
                                         RandomNumberGenerator& rng,
                                         const Private_Key* signing_key) {
   const std::string hostname = state.client_hello()->sni_hostname();
   const Kex_Algo kex_algo = state.ciphersuite().kex_method();

   if(kex_algo == Kex_Algo::PSK || kex_algo == Kex_Algo::ECDHE_PSK) {
      std::string identity_hint = creds.psk_identity_hint("tls-server", hostname);

      append_tls_length_value(m_params, identity_hint, 2);
   }

   if(kex_algo == Kex_Algo::DH) {
      const std::vector<Group_Params> dh_groups = state.client_hello()->supported_dh_groups();

      m_shared_group = Group_Params::NONE;

      /*
      If the client does not send any DH groups in the supported groups
      extension, but does offer DH ciphersuites, we select a group arbitrarily
      */

      if(dh_groups.empty()) {
         m_shared_group = policy.default_dh_group();
      } else {
         m_shared_group = policy.choose_key_exchange_group(dh_groups, {});
      }

      if(m_shared_group.value() == Group_Params::NONE)
         throw TLS_Exception(Alert::HandshakeFailure, "Could not agree on a DH group with the client");

      BOTAN_ASSERT(group_param_is_dh(m_shared_group.value()), "DH ciphersuite is using a finite field group");

      // Note: TLS 1.2 allows defining and using arbitrary DH groups (additional
      //       to the named and standardized ones). This API doesn't allow the
      //       server to make use of that at the moment. TLS 1.3 does not
      //       provide this flexibility!
      //
      // A possible implementation strategy in case one would ever need that:
      // `Policy::default_dh_group()` could return a `std::variant<Group_Params,
      // DL_Group>`, allowing it to define arbitrary groups.
      m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);
      auto dh = dynamic_cast<DH_PrivateKey*>(m_kex_key.get());
      if(!dh) {
         throw TLS_Exception(Alert::InternalError, "Application did not provide a Diffie-Hellman key");
      }

      append_tls_length_value(m_params, BigInt::encode(dh->get_int_field("p")), 2);
      append_tls_length_value(m_params, BigInt::encode(dh->get_int_field("g")), 2);
      append_tls_length_value(m_params, dh->public_value(), 2);
   } else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
      const std::vector<Group_Params> ec_groups = state.client_hello()->supported_ecc_curves();

      if(ec_groups.empty())
         throw Internal_Error("Client sent no ECC extension but we negotiated ECDH");

      m_shared_group = policy.choose_key_exchange_group(ec_groups, {});

      if(m_shared_group.value() == Group_Params::NONE)
         throw TLS_Exception(Alert::HandshakeFailure, "No shared ECC group with client");

      std::vector<uint8_t> ecdh_public_val;

      if(m_shared_group.value() == Group_Params::X25519) {
         m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);
         if(!m_kex_key) {
            throw TLS_Exception(Alert::InternalError, "Application did not provide a X25519 key");
         }
         ecdh_public_val = m_kex_key->public_value();
      } else {
         m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);
         auto ecdh = dynamic_cast<ECDH_PrivateKey*>(m_kex_key.get());
         if(!ecdh) {
            throw TLS_Exception(Alert::InternalError, "Application did not provide a EC-Diffie-Hellman key");
         }

         // follow client's preference for point compression
         ecdh_public_val =
            ecdh->public_value(state.client_hello()->prefers_compressed_ec_points() ? EC_Point_Format::Compressed
                                                                                    : EC_Point_Format::Uncompressed);
      }

      const uint16_t named_curve_id = static_cast<uint16_t>(m_shared_group.value());
      m_params.push_back(3);  // named curve
      m_params.push_back(get_byte<0>(named_curve_id));
      m_params.push_back(get_byte<1>(named_curve_id));

      append_tls_length_value(m_params, ecdh_public_val, 1);
   } else if(kex_algo != Kex_Algo::PSK) {
      throw Internal_Error("Server_Key_Exchange: Unknown kex type " + kex_method_to_string(kex_algo));
   }

   if(state.ciphersuite().signature_used()) {
      BOTAN_ASSERT(signing_key, "Signing key was set");

      std::pair<std::string, Signature_Format> format = state.choose_sig_format(*signing_key, m_scheme, false, policy);

      std::vector<uint8_t> buf = state.client_hello()->random();

      buf += state.server_hello()->random();
      buf += params();

      m_signature = state.callbacks().tls_sign_message(*signing_key, rng, format.first, format.second, buf);
   }

   state.hash().update(io.send(*this));
}

/**
* Deserialize a Server Key Exchange message
*/
Server_Key_Exchange::Server_Key_Exchange(const std::vector<uint8_t>& buf,
                                         const Kex_Algo kex_algo,
                                         const Auth_Method auth_method,
                                         Protocol_Version version) {
   BOTAN_UNUSED(version);  // remove this
   TLS_Data_Reader reader("ServerKeyExchange", buf);

   /*
   * Here we are deserializing enough to find out what offset the
   * signature is at. All processing is done when the Client Key Exchange
   * is prepared.
   */

   if(kex_algo == Kex_Algo::PSK || kex_algo == Kex_Algo::ECDHE_PSK) {
      reader.get_string(2, 0, 65535);  // identity hint
   }

   if(kex_algo == Kex_Algo::DH) {
      // 3 bigints, DH p, g, Y

      for(size_t i = 0; i != 3; ++i) {
         reader.get_range<uint8_t>(2, 1, 65535);
      }
   } else if(kex_algo == Kex_Algo::ECDH || kex_algo == Kex_Algo::ECDHE_PSK) {
      reader.get_byte();                     // curve type
      reader.get_uint16_t();                 // curve id
      reader.get_range<uint8_t>(1, 1, 255);  // public key
   } else if(kex_algo != Kex_Algo::PSK)
      throw Decoding_Error("Server_Key_Exchange: Unsupported kex type " + kex_method_to_string(kex_algo));

   m_params.assign(buf.data(), buf.data() + reader.read_so_far());

   if(auth_method != Auth_Method::IMPLICIT) {
      m_scheme = Signature_Scheme(reader.get_uint16_t());
      m_signature = reader.get_range<uint8_t>(2, 0, 65535);
   }

   reader.assert_done();
}

/**
* Serialize a Server Key Exchange message
*/
std::vector<uint8_t> Server_Key_Exchange::serialize() const {
   std::vector<uint8_t> buf = params();

   if(!m_signature.empty()) {
      if(m_scheme.is_set()) {
         buf.push_back(get_byte<0>(m_scheme.wire_code()));
         buf.push_back(get_byte<1>(m_scheme.wire_code()));
      }

      append_tls_length_value(buf, m_signature, 2);
   }

   return buf;
}

/**
* Verify a Server Key Exchange message
*/
bool Server_Key_Exchange::verify(const Public_Key& server_key,
                                 const Handshake_State& state,
                                 const Policy& policy) const {
   policy.check_peer_key_acceptable(server_key);

   std::pair<std::string, Signature_Format> format =
      state.parse_sig_format(server_key, m_scheme, state.client_hello()->signature_schemes(), false, policy);

   std::vector<uint8_t> buf = state.client_hello()->random();

   buf += state.server_hello()->random();
   buf += params();

   const bool signature_valid =
      state.callbacks().tls_verify_message(server_key, format.first, format.second, buf, m_signature);

#if defined(BOTAN_UNSAFE_FUZZER_MODE)
   BOTAN_UNUSED(signature_valid);
   return true;
#else
   return signature_valid;
#endif
}

const PK_Key_Agreement_Key& Server_Key_Exchange::server_kex_key() const {
   BOTAN_ASSERT_NONNULL(m_kex_key);
   return *m_kex_key;
}

}  // namespace Botan::TLS

1	/*
2	* Server Key Exchange Message
3	* (C) 2004-2010,2012,2015,2016 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/credentials_manager.h>
12	#include <botan/pubkey.h>
13	#include <botan/tls_extensions.h>
14	#include <botan/internal/loadstor.h>
15	#include <botan/internal/tls_handshake_io.h>
16	#include <botan/internal/tls_handshake_state.h>
17	#include <botan/internal/tls_reader.h>
18
19	#include <botan/dh.h>
20	#include <botan/dl_group.h>
21	#include <botan/ecdh.h>
22
23	#if defined(BOTAN_HAS_CURVE_25519)
24	#include <botan/curve25519.h>
25	#endif
26
27	namespace Botan::TLS {
28
29	/**
30	* Create a new Server Key Exchange message
31	*/
32	Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,	605✔
33	Handshake_State& state,
34	const Policy& policy,
35	Credentials_Manager& creds,
36	RandomNumberGenerator& rng,
37	const Private_Key* signing_key) {	605✔
38	const std::string hostname = state.client_hello()->sni_hostname();	605✔
39	const Kex_Algo kex_algo = state.ciphersuite().kex_method();	605✔
40
41	if(kex_algo == Kex_Algo::PSK \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	605✔
42	std::string identity_hint = creds.psk_identity_hint("tls-server", hostname);	44✔
43
44	append_tls_length_value(m_params, identity_hint, 2);	88✔
45	}	44✔
46
47	if(kex_algo == Kex_Algo::DH) {	605✔
48	const std::vector<Group_Params> dh_groups = state.client_hello()->supported_dh_groups();	4✔
49
50	m_shared_group = Group_Params::NONE;	4✔
51
52	/*
53	If the client does not send any DH groups in the supported groups
54	extension, but does offer DH ciphersuites, we select a group arbitrarily
55	*/
56
57	if(dh_groups.empty()) {	4✔
58	m_shared_group = policy.default_dh_group();	×
59	} else {
60	m_shared_group = policy.choose_key_exchange_group(dh_groups, {});	4✔
61	}
62
63	if(m_shared_group.value() == Group_Params::NONE)	4✔
64	throw TLS_Exception(Alert::HandshakeFailure, "Could not agree on a DH group with the client");	×
65
66	BOTAN_ASSERT(group_param_is_dh(m_shared_group.value()), "DH ciphersuite is using a finite field group");	4✔
67
68	// Note: TLS 1.2 allows defining and using arbitrary DH groups (additional
69	// to the named and standardized ones). This API doesn't allow the
70	// server to make use of that at the moment. TLS 1.3 does not
71	// provide this flexibility!
72	//
73	// A possible implementation strategy in case one would ever need that:
74	// `Policy::default_dh_group()` could return a `std::variant<Group_Params,
75	// DL_Group>`, allowing it to define arbitrary groups.
76	m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);	4✔
77	auto dh = dynamic_cast<DH_PrivateKey*>(m_kex_key.get());	4✔
78	if(!dh) {	4✔
79	throw TLS_Exception(Alert::InternalError, "Application did not provide a Diffie-Hellman key");	×
80	}
81
82	append_tls_length_value(m_params, BigInt::encode(dh->get_int_field("p")), 2);	8✔
83	append_tls_length_value(m_params, BigInt::encode(dh->get_int_field("g")), 2);	8✔
84	append_tls_length_value(m_params, dh->public_value(), 2);	12✔
85	} else if(kex_algo == Kex_Algo::ECDH \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	605✔
86	const std::vector<Group_Params> ec_groups = state.client_hello()->supported_ecc_curves();	568✔
87
88	if(ec_groups.empty())	568✔
89	throw Internal_Error("Client sent no ECC extension but we negotiated ECDH");	×
90
91	m_shared_group = policy.choose_key_exchange_group(ec_groups, {});	568✔
92
93	if(m_shared_group.value() == Group_Params::NONE)	568✔
94	throw TLS_Exception(Alert::HandshakeFailure, "No shared ECC group with client");	×
95
96	std::vector<uint8_t> ecdh_public_val;	568✔
97
98	if(m_shared_group.value() == Group_Params::X25519) {
99	m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);	499✔
100	if(!m_kex_key) {	499✔
101	throw TLS_Exception(Alert::InternalError, "Application did not provide a X25519 key");	×
102	}
103	ecdh_public_val = m_kex_key->public_value();	998✔
104	} else {
105	m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);	69✔
106	auto ecdh = dynamic_cast<ECDH_PrivateKey*>(m_kex_key.get());	69✔
107	if(!ecdh) {	69✔
108	throw TLS_Exception(Alert::InternalError, "Application did not provide a EC-Diffie-Hellman key");	×
109	}
110
111	// follow client's preference for point compression
112	ecdh_public_val =	69✔
113	ecdh->public_value(state.client_hello()->prefers_compressed_ec_points() ? EC_Point_Format::Compressed	207✔
114	: EC_Point_Format::Uncompressed);	69✔
115	}
116
117	const uint16_t named_curve_id = static_cast<uint16_t>(m_shared_group.value());	568✔
118	m_params.push_back(3); // named curve	568✔
119	m_params.push_back(get_byte<0>(named_curve_id));	568✔
120	m_params.push_back(get_byte<1>(named_curve_id));	568✔
121
122	append_tls_length_value(m_params, ecdh_public_val, 1);	1,136✔
123	} else if(kex_algo != Kex_Algo::PSK) {	1,169✔
124	throw Internal_Error("Server_Key_Exchange: Unknown kex type " + kex_method_to_string(kex_algo));	×
125	}
126
127	if(state.ciphersuite().signature_used()) {	605✔
128	BOTAN_ASSERT(signing_key, "Signing key was set");	561✔
129
130	std::pair<std::string, Signature_Format> format = state.choose_sig_format(*signing_key, m_scheme, false, policy);	561✔
131
132	std::vector<uint8_t> buf = state.client_hello()->random();	561✔
133
134	buf += state.server_hello()->random();	561✔
135	buf += params();	561✔
136
137	m_signature = state.callbacks().tls_sign_message(*signing_key, rng, format.first, format.second, buf);	561✔
138	}	1,010✔
139
140	state.hash().update(io.send(*this));	1,811✔
141	}	609✔
142
143	/**
144	* Deserialize a Server Key Exchange message
145	*/
146	Server_Key_Exchange::Server_Key_Exchange(const std::vector<uint8_t>& buf,	746✔
147	const Kex_Algo kex_algo,
148	const Auth_Method auth_method,
149	Protocol_Version version) {	746✔
150	BOTAN_UNUSED(version); // remove this	746✔
151	TLS_Data_Reader reader("ServerKeyExchange", buf);	746✔
152
153	/*
154	* Here we are deserializing enough to find out what offset the
155	* signature is at. All processing is done when the Client Key Exchange
156	* is prepared.
157	*/
158
159	if(kex_algo == Kex_Algo::PSK \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	746✔
160	reader.get_string(2, 0, 65535); // identity hint	102✔
161	}
162
163	if(kex_algo == Kex_Algo::DH) {	746✔
164	// 3 bigints, DH p, g, Y
165
166	for(size_t i = 0; i != 3; ++i) {	16✔
167	reader.get_range<uint8_t>(2, 1, 65535);	24✔
168	}
169	} else if(kex_algo == Kex_Algo::ECDH \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	742✔
170	reader.get_byte(); // curve type	716✔
171	reader.get_uint16_t(); // curve id	716✔
172	reader.get_range<uint8_t>(1, 1, 255); // public key	1,432✔
173	} else if(kex_algo != Kex_Algo::PSK)	26✔
174	throw Decoding_Error("Server_Key_Exchange: Unsupported kex type " + kex_method_to_string(kex_algo));	×
175
176	m_params.assign(buf.data(), buf.data() + reader.read_so_far());	746✔
177
178	if(auth_method != Auth_Method::IMPLICIT) {	746✔
179	m_scheme = Signature_Scheme(reader.get_uint16_t());	695✔
180	m_signature = reader.get_range<uint8_t>(2, 0, 65535);	695✔
181	}
182
183	reader.assert_done();	746✔
184	}	750✔
185
186	/**
187	* Serialize a Server Key Exchange message
188	*/
189	std::vector<uint8_t> Server_Key_Exchange::serialize() const {	605✔
190	std::vector<uint8_t> buf = params();	605✔
191
192	if(!m_signature.empty()) {	605✔
193	if(m_scheme.is_set()) {	561✔
194	buf.push_back(get_byte<0>(m_scheme.wire_code()));	561✔
195	buf.push_back(get_byte<1>(m_scheme.wire_code()));	561✔
196	}
197
198	append_tls_length_value(buf, m_signature, 2);	561✔
199	}
200
201	return buf;	605✔
202	}	×
203
204	/**
205	* Verify a Server Key Exchange message
206	*/
207	bool Server_Key_Exchange::verify(const Public_Key& server_key,	693✔
208	const Handshake_State& state,
209	const Policy& policy) const {
210	policy.check_peer_key_acceptable(server_key);	693✔
211
212	std::pair<std::string, Signature_Format> format =	693✔
213	state.parse_sig_format(server_key, m_scheme, state.client_hello()->signature_schemes(), false, policy);	693✔
214
215	std::vector<uint8_t> buf = state.client_hello()->random();	691✔
216
217	buf += state.server_hello()->random();	691✔
218	buf += params();	691✔
219
220	const bool signature_valid =	691✔
221	state.callbacks().tls_verify_message(server_key, format.first, format.second, buf, m_signature);	691✔
222
223	#if defined(BOTAN_UNSAFE_FUZZER_MODE)
224	BOTAN_UNUSED(signature_valid);
225	return true;
226	#else
227	return signature_valid;	691✔
228	#endif
229	}	1,248✔
230
231	const PK_Key_Agreement_Key& Server_Key_Exchange::server_kex_key() const {	557✔
232	BOTAN_ASSERT_NONNULL(m_kex_key);	557✔
233	return *m_kex_key;	557✔
234	}
235
236	} // namespace Botan::TLS

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