21753596263

Committed 06 Feb 2026 02:13PM UTC coverage: 90.063% (-0.01%) from 90.073%

Build # 21753596263

Build Type

Pull #5289

github

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web-flow

Commit Message

Merge 587099284 into 8ea0ca252

Pull Request Pull Request #5289: Further misc header reductions, forward declarations, etc

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91.26

/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_12.h>

#include <botan/credentials_manager.h>
#include <botan/dl_group.h>
#include <botan/pubkey.h>
#include <botan/tls_callbacks.h>
#include <botan/tls_extensions.h>
#include <botan/tls_policy.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/target_info.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>

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) {
      const 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;

      /*
      RFC 7919 requires that if the client sends any groups in the FFDHE
      range, that we must select one of these. If this is not possible,
      then we are required to reject the connection.

      If the client did not send any DH groups, but did offer DH ciphersuites
      and we selected one, then consult the policy for which DH group to pick.
      */

      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");
      }

      // The policy had better return a group we know about:
      BOTAN_ASSERT(m_shared_group.value().is_dh_named_group(), "DH ciphersuite is using a known 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 == nullptr) {
         throw TLS_Exception(Alert::InternalError, "Application did not provide a Diffie-Hellman key");
      }

      append_tls_length_value(m_params, dh->get_int_field("p").serialize(), 2);
      append_tls_length_value(m_params, dh->get_int_field("g").serialize(), 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");
      }

      m_kex_key = [&] {
         if(m_shared_group->is_ecdh_named_curve()) {
            const auto pubkey_point_format = state.client_hello()->prefers_compressed_ec_points()
                                                ? EC_Point_Format::Compressed
                                                : EC_Point_Format::Uncompressed;
            return state.callbacks().tls12_generate_ephemeral_ecdh_key(*m_shared_group, rng, pubkey_point_format);
         } else {
            return state.callbacks().tls_generate_ephemeral_key(*m_shared_group, rng);
         }
      }();

      if(!m_kex_key) {
         throw TLS_Exception(Alert::InternalError, "Application did not provide an EC key");
      }

      const uint16_t named_curve_id = m_shared_group.value().wire_code();
      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));

      // Note: In contrast to public_value(), raw_public_key_bits() takes the
      // point format (compressed vs. uncompressed) into account that was set
      // in its construction within tls_generate_ephemeral_key().
      append_tls_length_value(m_params, m_kex_key->raw_public_key_bits(), 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");

      const 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);

   const 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_12.h>
10
11	#include <botan/credentials_manager.h>
12	#include <botan/dl_group.h>
13	#include <botan/pubkey.h>
14	#include <botan/tls_callbacks.h>
15	#include <botan/tls_extensions.h>
16	#include <botan/tls_policy.h>
17	#include <botan/internal/loadstor.h>
18	#include <botan/internal/target_info.h>
19	#include <botan/internal/tls_handshake_io.h>
20	#include <botan/internal/tls_handshake_state.h>
21	#include <botan/internal/tls_reader.h>
22
23	#include <botan/dh.h>
24
25	namespace Botan::TLS {
26
27	/**
28	* Create a new Server Key Exchange message
29	*/
30	Server_Key_Exchange::Server_Key_Exchange(Handshake_IO& io,	659✔
31	Handshake_State& state,
32	const Policy& policy,
33	Credentials_Manager& creds,
34	RandomNumberGenerator& rng,
35	const Private_Key* signing_key) {	659✔
36	const std::string hostname = state.client_hello()->sni_hostname();	659✔
37	const Kex_Algo kex_algo = state.ciphersuite().kex_method();	659✔
38
39	if(kex_algo == Kex_Algo::PSK \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	659✔
40	const std::string identity_hint = creds.psk_identity_hint("tls-server", hostname);	50✔
41
42	append_tls_length_value(m_params, identity_hint, 2);	100✔
43	}	50✔
44
45	if(kex_algo == Kex_Algo::DH) {	659✔
46	const std::vector<Group_Params> dh_groups = state.client_hello()->supported_dh_groups();	6✔
47
48	m_shared_group = Group_Params::NONE;	6✔
49
50	/*
51	RFC 7919 requires that if the client sends any groups in the FFDHE
52	range, that we must select one of these. If this is not possible,
53	then we are required to reject the connection.
54
55	If the client did not send any DH groups, but did offer DH ciphersuites
56	and we selected one, then consult the policy for which DH group to pick.
57	*/
58
59	if(dh_groups.empty()) {	6✔
60	m_shared_group = policy.default_dh_group();	×
61	} else {
62	m_shared_group = policy.choose_key_exchange_group(dh_groups, {});	12✔
63	}
64
65	if(m_shared_group.value() == Group_Params::NONE) {	6✔
66	throw TLS_Exception(Alert::HandshakeFailure, "Could not agree on a DH group with the client");	×
67	}
68
69	// The policy had better return a group we know about:
70	BOTAN_ASSERT(m_shared_group.value().is_dh_named_group(), "DH ciphersuite is using a known finite field group");	6✔
71
72	// Note: TLS 1.2 allows defining and using arbitrary DH groups (additional
73	// to the named and standardized ones). This API doesn't allow the
74	// server to make use of that at the moment. TLS 1.3 does not
75	// provide this flexibility!
76	//
77	// A possible implementation strategy in case one would ever need that:
78	// `Policy::default_dh_group()` could return a `std::variant<Group_Params,
79	// DL_Group>`, allowing it to define arbitrary groups.
80	m_kex_key = state.callbacks().tls_generate_ephemeral_key(m_shared_group.value(), rng);	6✔
81	auto* dh = dynamic_cast<DH_PrivateKey*>(m_kex_key.get());	6✔
82	if(dh == nullptr) {	6✔
83	throw TLS_Exception(Alert::InternalError, "Application did not provide a Diffie-Hellman key");	×
84	}
85
86	append_tls_length_value(m_params, dh->get_int_field("p").serialize(), 2);	18✔
87	append_tls_length_value(m_params, dh->get_int_field("g").serialize(), 2);	18✔
88	append_tls_length_value(m_params, dh->public_value(), 2);	18✔
89	} else if(kex_algo == Kex_Algo::ECDH \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	659✔
90	const std::vector<Group_Params> ec_groups = state.client_hello()->supported_ecc_curves();	615✔
91
92	if(ec_groups.empty()) {	615✔
93	throw Internal_Error("Client sent no ECC extension but we negotiated ECDH");	×
94	}
95
96	m_shared_group = policy.choose_key_exchange_group(ec_groups, {});	1,230✔
97
98	if(m_shared_group.value() == Group_Params::NONE) {	615✔
99	throw TLS_Exception(Alert::HandshakeFailure, "No shared ECC group with client");	×
100	}
101
102	m_kex_key = [&] {	1,845✔
103	if(m_shared_group->is_ecdh_named_curve()) {	615✔
104	const auto pubkey_point_format = state.client_hello()->prefers_compressed_ec_points()	28✔
105	? EC_Point_Format::Compressed	28✔
106	: EC_Point_Format::Uncompressed;	28✔
107	return state.callbacks().tls12_generate_ephemeral_ecdh_key(*m_shared_group, rng, pubkey_point_format);	28✔
108	} else {
109	return state.callbacks().tls_generate_ephemeral_key(*m_shared_group, rng);	1,174✔
110	}
111	}();	615✔
112
113	if(!m_kex_key) {	615✔
114	throw TLS_Exception(Alert::InternalError, "Application did not provide an EC key");	×
115	}
116
117	const uint16_t named_curve_id = m_shared_group.value().wire_code();	615✔
118	m_params.push_back(3); // named curve	615✔
119	m_params.push_back(get_byte<0>(named_curve_id));	615✔
120	m_params.push_back(get_byte<1>(named_curve_id));	615✔
121
122	// Note: In contrast to public_value(), raw_public_key_bits() takes the
123	// point format (compressed vs. uncompressed) into account that was set
124	// in its construction within tls_generate_ephemeral_key().
125	append_tls_length_value(m_params, m_kex_key->raw_public_key_bits(), 1);	1,845✔
126	} else if(kex_algo != Kex_Algo::PSK) {	653✔
127	throw Internal_Error("Server_Key_Exchange: Unknown kex type " + kex_method_to_string(kex_algo));	×
128	}
129
130	if(state.ciphersuite().signature_used()) {	659✔
131	BOTAN_ASSERT(signing_key, "Signing key was set");	609✔
132
133	const std::pair<std::string, Signature_Format> format =	609✔
134	state.choose_sig_format(*signing_key, m_scheme, false, policy);	609✔
135
136	std::vector<uint8_t> buf = state.client_hello()->random();	609✔
137
138	buf += state.server_hello()->random();	609✔
139	buf += params();	609✔
140
141	m_signature = state.callbacks().tls_sign_message(*signing_key, rng, format.first, format.second, buf);	609✔
142	}	609✔
143
144	state.hash().update(io.send(*this));	1,975✔
145	}	661✔
146
147	/**
148	* Deserialize a Server Key Exchange message
149	*/
150	Server_Key_Exchange::Server_Key_Exchange(const std::vector<uint8_t>& buf,	1,006✔
151	const Kex_Algo kex_algo,
152	const Auth_Method auth_method,
153	Protocol_Version version) {	1,006✔
154	BOTAN_UNUSED(version); // remove this	1,006✔
155	TLS_Data_Reader reader("ServerKeyExchange", buf);	1,006✔
156
157	/*
158	* Here we are deserializing enough to find out what offset the
159	* signature is at. All processing is done when the Client Key Exchange
160	* is prepared.
161	*/
162
163	if(kex_algo == Kex_Algo::PSK \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	1,006✔
164	reader.get_string(2, 0, 65535); // identity hint	114✔
165	}
166
167	if(kex_algo == Kex_Algo::DH) {	1,006✔
168	// 3 bigints, DH p, g, Y
169
170	for(size_t i = 0; i != 3; ++i) {	95✔
171	reader.get_range<uint8_t>(2, 1, 65535);	143✔
172	}
173	} else if(kex_algo == Kex_Algo::ECDH \|\| kex_algo == Kex_Algo::ECDHE_PSK) {	979✔
174	reader.get_byte(); // curve type	948✔
175	reader.get_uint16_t(); // curve id	947✔
176	reader.get_range<uint8_t>(1, 1, 255); // public key	1,891✔
177	} else if(kex_algo != Kex_Algo::PSK) {	31✔
178	throw Decoding_Error("Server_Key_Exchange: Unsupported kex type " + kex_method_to_string(kex_algo));	×
179	}
180
181	m_params.assign(buf.data(), buf.data() + reader.read_so_far());	996✔
182
183	if(auth_method != Auth_Method::IMPLICIT) {	996✔
184	m_scheme = Signature_Scheme(reader.get_uint16_t());	939✔
185	m_signature = reader.get_range<uint8_t>(2, 0, 65535);	936✔
186	}
187
188	reader.assert_done();	988✔
189	}	1,022✔
190
191	/**
192	* Serialize a Server Key Exchange message
193	*/
194	std::vector<uint8_t> Server_Key_Exchange::serialize() const {	659✔
195	std::vector<uint8_t> buf = params();	659✔
196
197	if(!m_signature.empty()) {	659✔
198	if(m_scheme.is_set()) {	609✔
199	buf.push_back(get_byte<0>(m_scheme.wire_code()));	609✔
200	buf.push_back(get_byte<1>(m_scheme.wire_code()));	609✔
201	}
202
203	append_tls_length_value(buf, m_signature, 2);	609✔
204	}
205
206	return buf;	659✔
207	}	×
208
209	/**
210	* Verify a Server Key Exchange message
211	*/
212	bool Server_Key_Exchange::verify(const Public_Key& server_key,	927✔
213	const Handshake_State& state,
214	const Policy& policy) const {
215	policy.check_peer_key_acceptable(server_key);	927✔
216
217	const std::pair<std::string, Signature_Format> format =	878✔
218	state.parse_sig_format(server_key, m_scheme, state.client_hello()->signature_schemes(), false, policy);	878✔
219
220	std::vector<uint8_t> buf = state.client_hello()->random();	869✔
221
222	buf += state.server_hello()->random();	869✔
223	buf += params();	869✔
224
225	const bool signature_valid =	869✔
226	state.callbacks().tls_verify_message(server_key, format.first, format.second, buf, m_signature);	869✔
227
228	#if defined(BOTAN_UNSAFE_FUZZER_MODE)
229	BOTAN_UNUSED(signature_valid);
230	return true;
231	#else
232	return signature_valid;	869✔
233	#endif
234	}	869✔
235
236	const PK_Key_Agreement_Key& Server_Key_Exchange::server_kex_key() const {	606✔
237	BOTAN_ASSERT_NONNULL(m_kex_key);	606✔
238	return *m_kex_key;	606✔
239	}
240
241	} // namespace Botan::TLS

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