1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // This code implements SPAKE2, a variant of EKE: 6 // http://www.di.ens.fr/~pointche/pub.php?reference=AbPo04 7 8 #include "crypto/p224_spake.h" 9 10 #include <algorithm> 11 12 #include "base/logging.h" 13 #include "crypto/p224.h" 14 #include "crypto/random.h" 15 #include "crypto/secure_util.h" 16 17 namespace { 18 19 // The following two points (M and N in the protocol) are verifiable random 20 // points on the curve and can be generated with the following code: 21 22 // #include <stdint.h> 23 // #include <stdio.h> 24 // #include <string.h> 25 // 26 // #include <openssl/ec.h> 27 // #include <openssl/obj_mac.h> 28 // #include <openssl/sha.h> 29 // 30 // // Silence a presubmit. 31 // #define PRINTF printf 32 // 33 // static const char kSeed1[] = "P224 point generation seed (M)"; 34 // static const char kSeed2[] = "P224 point generation seed (N)"; 35 // 36 // void find_seed(const char* seed) { 37 // SHA256_CTX sha256; 38 // uint8_t digest[SHA256_DIGEST_LENGTH]; 39 // 40 // SHA256_Init(&sha256); 41 // SHA256_Update(&sha256, seed, strlen(seed)); 42 // SHA256_Final(digest, &sha256); 43 // 44 // BIGNUM x, y; 45 // EC_GROUP* p224 = EC_GROUP_new_by_curve_name(NID_secp224r1); 46 // EC_POINT* p = EC_POINT_new(p224); 47 // 48 // for (unsigned i = 0;; i++) { 49 // BN_init(&x); 50 // BN_bin2bn(digest, 28, &x); 51 // 52 // if (EC_POINT_set_compressed_coordinates_GFp( 53 // p224, p, &x, digest[28] & 1, NULL)) { 54 // BN_init(&y); 55 // EC_POINT_get_affine_coordinates_GFp(p224, p, &x, &y, NULL); 56 // char* x_str = BN_bn2hex(&x); 57 // char* y_str = BN_bn2hex(&y); 58 // PRINTF("Found after %u iterations:\n%s\n%s\n", i, x_str, y_str); 59 // OPENSSL_free(x_str); 60 // OPENSSL_free(y_str); 61 // BN_free(&x); 62 // BN_free(&y); 63 // break; 64 // } 65 // 66 // SHA256_Init(&sha256); 67 // SHA256_Update(&sha256, digest, sizeof(digest)); 68 // SHA256_Final(digest, &sha256); 69 // 70 // BN_free(&x); 71 // } 72 // 73 // EC_POINT_free(p); 74 // EC_GROUP_free(p224); 75 // } 76 // 77 // int main() { 78 // find_seed(kSeed1); 79 // find_seed(kSeed2); 80 // return 0; 81 // } 82 83 const crypto::p224::Point kM = { 84 {174237515, 77186811, 235213682, 33849492, 85 33188520, 48266885, 177021753, 81038478}, 86 {104523827, 245682244, 266509668, 236196369, 87 28372046, 145351378, 198520366, 113345994}, 88 {1, 0, 0, 0, 0, 0, 0, 0}, 89 }; 90 91 const crypto::p224::Point kN = { 92 {136176322, 263523628, 251628795, 229292285, 93 5034302, 185981975, 171998428, 11653062}, 94 {197567436, 51226044, 60372156, 175772188, 95 42075930, 8083165, 160827401, 65097570}, 96 {1, 0, 0, 0, 0, 0, 0, 0}, 97 }; 98 99 } // anonymous namespace 100 101 namespace crypto { 102 103 P224EncryptedKeyExchange::P224EncryptedKeyExchange(PeerType peer_type, 104 base::StringPiece password) 105 : state_(kStateInitial), is_server_(peer_type == kPeerTypeServer) { 106 memset(&x_, 0, sizeof(x_)); 107 memset(&expected_authenticator_, 0, sizeof(expected_authenticator_)); 108 109 // x_ is a random scalar. 110 RandBytes(x_, sizeof(x_)); 111 112 // Calculate |password| hash to get SPAKE password value. 113 SHA256HashString(std::string(password.data(), password.length()), 114 pw_, sizeof(pw_)); 115 116 Init(); 117 } 118 119 void P224EncryptedKeyExchange::Init() { 120 // X = g**x_ 121 p224::Point X; 122 p224::ScalarBaseMult(x_, &X); 123 124 // The client masks the Diffie-Hellman value, X, by adding M**pw and the 125 // server uses N**pw. 126 p224::Point MNpw; 127 p224::ScalarMult(is_server_ ? kN : kM, pw_, &MNpw); 128 129 // X* = X + (N|M)**pw 130 p224::Point Xstar; 131 p224::Add(X, MNpw, &Xstar); 132 133 next_message_ = Xstar.ToString(); 134 } 135 136 const std::string& P224EncryptedKeyExchange::GetNextMessage() { 137 if (state_ == kStateInitial) { 138 state_ = kStateRecvDH; 139 return next_message_; 140 } else if (state_ == kStateSendHash) { 141 state_ = kStateRecvHash; 142 return next_message_; 143 } 144 145 LOG(FATAL) << "P224EncryptedKeyExchange::GetNextMessage called in" 146 " bad state " << state_; 147 next_message_ = ""; 148 return next_message_; 149 } 150 151 P224EncryptedKeyExchange::Result P224EncryptedKeyExchange::ProcessMessage( 152 base::StringPiece message) { 153 if (state_ == kStateRecvHash) { 154 // This is the final state of the protocol: we are reading the peer's 155 // authentication hash and checking that it matches the one that we expect. 156 if (message.size() != sizeof(expected_authenticator_)) { 157 error_ = "peer's hash had an incorrect size"; 158 return kResultFailed; 159 } 160 if (!SecureMemEqual(message.data(), expected_authenticator_, 161 message.size())) { 162 error_ = "peer's hash had incorrect value"; 163 return kResultFailed; 164 } 165 state_ = kStateDone; 166 return kResultSuccess; 167 } 168 169 if (state_ != kStateRecvDH) { 170 LOG(FATAL) << "P224EncryptedKeyExchange::ProcessMessage called in" 171 " bad state " << state_; 172 error_ = "internal error"; 173 return kResultFailed; 174 } 175 176 // Y* is the other party's masked, Diffie-Hellman value. 177 p224::Point Ystar; 178 if (!Ystar.SetFromString(message)) { 179 error_ = "failed to parse peer's masked Diffie-Hellman value"; 180 return kResultFailed; 181 } 182 183 // We calculate the mask value: (N|M)**pw 184 p224::Point MNpw, minus_MNpw, Y, k; 185 p224::ScalarMult(is_server_ ? kM : kN, pw_, &MNpw); 186 p224::Negate(MNpw, &minus_MNpw); 187 188 // Y = Y* - (N|M)**pw 189 p224::Add(Ystar, minus_MNpw, &Y); 190 191 // K = Y**x_ 192 p224::ScalarMult(Y, x_, &k); 193 194 // If everything worked out, then K is the same for both parties. 195 key_ = k.ToString(); 196 197 std::string client_masked_dh, server_masked_dh; 198 if (is_server_) { 199 client_masked_dh = message.as_string(); 200 server_masked_dh = next_message_; 201 } else { 202 client_masked_dh = next_message_; 203 server_masked_dh = message.as_string(); 204 } 205 206 // Now we calculate the hashes that each side will use to prove to the other 207 // that they derived the correct value for K. 208 uint8_t client_hash[kSHA256Length], server_hash[kSHA256Length]; 209 CalculateHash(kPeerTypeClient, client_masked_dh, server_masked_dh, key_, 210 client_hash); 211 CalculateHash(kPeerTypeServer, client_masked_dh, server_masked_dh, key_, 212 server_hash); 213 214 const uint8_t* my_hash = is_server_ ? server_hash : client_hash; 215 const uint8_t* their_hash = is_server_ ? client_hash : server_hash; 216 217 next_message_ = 218 std::string(reinterpret_cast<const char*>(my_hash), kSHA256Length); 219 memcpy(expected_authenticator_, their_hash, kSHA256Length); 220 state_ = kStateSendHash; 221 return kResultPending; 222 } 223 224 void P224EncryptedKeyExchange::CalculateHash( 225 PeerType peer_type, 226 const std::string& client_masked_dh, 227 const std::string& server_masked_dh, 228 const std::string& k, 229 uint8_t* out_digest) { 230 std::string hash_contents; 231 232 if (peer_type == kPeerTypeServer) { 233 hash_contents = "server"; 234 } else { 235 hash_contents = "client"; 236 } 237 238 hash_contents += client_masked_dh; 239 hash_contents += server_masked_dh; 240 hash_contents += 241 std::string(reinterpret_cast<const char *>(pw_), sizeof(pw_)); 242 hash_contents += k; 243 244 SHA256HashString(hash_contents, out_digest, kSHA256Length); 245 } 246 247 const std::string& P224EncryptedKeyExchange::error() const { 248 return error_; 249 } 250 251 const std::string& P224EncryptedKeyExchange::GetKey() const { 252 DCHECK_EQ(state_, kStateDone); 253 return GetUnverifiedKey(); 254 } 255 256 const std::string& P224EncryptedKeyExchange::GetUnverifiedKey() const { 257 // Key is already final when state is kStateSendHash. Subsequent states are 258 // used only for verification of the key. Some users may combine verification 259 // with sending verifiable data instead of |expected_authenticator_|. 260 DCHECK_GE(state_, kStateSendHash); 261 return key_; 262 } 263 264 void P224EncryptedKeyExchange::SetXForTesting(const std::string& x) { 265 memset(&x_, 0, sizeof(x_)); 266 memcpy(&x_, x.data(), std::min(x.size(), sizeof(x_))); 267 Init(); 268 } 269 270 } // namespace crypto 271
