1 // Copyright 2013 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 #include "google_apis/cup/client_update_protocol.h" 6 7 #include "base/base64.h" 8 #include "base/logging.h" 9 #include "base/memory/scoped_ptr.h" 10 #include "base/sha1.h" 11 #include "base/strings/string_util.h" 12 #include "base/strings/stringprintf.h" 13 #include "crypto/hmac.h" 14 #include "crypto/random.h" 15 16 namespace { 17 18 base::StringPiece ByteVectorToSP(const std::vector<uint8>& vec) { 19 if (vec.empty()) 20 return base::StringPiece(); 21 22 return base::StringPiece(reinterpret_cast<const char*>(&vec[0]), vec.size()); 23 } 24 25 // This class needs to implement the same hashing and signing functions as the 26 // Google Update server; for now, this is SHA-1 and HMAC-SHA1, but this may 27 // change to SHA-256 in the near future. For this reason, all primitives are 28 // wrapped. The name "SymSign" is used to mirror the CUP specification. 29 size_t HashDigestSize() { 30 return base::kSHA1Length; 31 } 32 33 std::vector<uint8> Hash(const std::vector<uint8>& data) { 34 std::vector<uint8> result(HashDigestSize()); 35 base::SHA1HashBytes(data.empty() ? NULL : &data[0], 36 data.size(), 37 &result[0]); 38 return result; 39 } 40 41 std::vector<uint8> Hash(const base::StringPiece& sdata) { 42 std::vector<uint8> result(HashDigestSize()); 43 base::SHA1HashBytes(sdata.empty() ? 44 NULL : 45 reinterpret_cast<const unsigned char*>(sdata.data()), 46 sdata.length(), 47 &result[0]); 48 return result; 49 } 50 51 std::vector<uint8> SymConcat(uint8 id, 52 const std::vector<uint8>* h1, 53 const std::vector<uint8>* h2, 54 const std::vector<uint8>* h3) { 55 std::vector<uint8> result; 56 result.push_back(id); 57 const std::vector<uint8>* args[] = { h1, h2, h3 }; 58 for (size_t i = 0; i != arraysize(args); ++i) { 59 if (args[i]) { 60 DCHECK_EQ(args[i]->size(), HashDigestSize()); 61 result.insert(result.end(), args[i]->begin(), args[i]->end()); 62 } 63 } 64 65 return result; 66 } 67 68 std::vector<uint8> SymSign(const std::vector<uint8>& key, 69 const std::vector<uint8>& hashes) { 70 DCHECK(!key.empty()); 71 DCHECK(!hashes.empty()); 72 73 crypto::HMAC hmac(crypto::HMAC::SHA1); 74 if (!hmac.Init(&key[0], key.size())) 75 return std::vector<uint8>(); 76 77 std::vector<uint8> result(hmac.DigestLength()); 78 if (!hmac.Sign(ByteVectorToSP(hashes), &result[0], result.size())) 79 return std::vector<uint8>(); 80 81 return result; 82 } 83 84 bool SymSignVerify(const std::vector<uint8>& key, 85 const std::vector<uint8>& hashes, 86 const std::vector<uint8>& server_proof) { 87 DCHECK(!key.empty()); 88 DCHECK(!hashes.empty()); 89 DCHECK(!server_proof.empty()); 90 91 crypto::HMAC hmac(crypto::HMAC::SHA1); 92 if (!hmac.Init(&key[0], key.size())) 93 return false; 94 95 return hmac.Verify(ByteVectorToSP(hashes), ByteVectorToSP(server_proof)); 96 } 97 98 // RsaPad() is implemented as described in the CUP spec. It is NOT a general 99 // purpose padding algorithm. 100 std::vector<uint8> RsaPad(size_t rsa_key_size, 101 const std::vector<uint8>& entropy) { 102 DCHECK_GE(rsa_key_size, HashDigestSize()); 103 104 // The result gets padded with zeros if the result size is greater than 105 // the size of the buffer provided by the caller. 106 std::vector<uint8> result(entropy); 107 result.resize(rsa_key_size - HashDigestSize()); 108 109 // For use with RSA, the input needs to be smaller than the RSA modulus, 110 // which has always the msb set. 111 result[0] &= 127; // Reset msb 112 result[0] |= 64; // Set second highest bit. 113 114 std::vector<uint8> digest = Hash(result); 115 result.insert(result.end(), digest.begin(), digest.end()); 116 DCHECK_EQ(result.size(), rsa_key_size); 117 return result; 118 } 119 120 // CUP passes the versioned secret in the query portion of the URL for the 121 // update check service -- and that means that a URL-safe variant of Base64 is 122 // needed. Call the standard Base64 encoder/decoder and then apply fixups. 123 std::string UrlSafeB64Encode(const std::vector<uint8>& data) { 124 std::string result; 125 base::Base64Encode(ByteVectorToSP(data), &result); 126 127 // Do an tr|+/|-_| on the output, and strip any '=' padding. 128 for (std::string::iterator it = result.begin(); it != result.end(); ++it) { 129 switch (*it) { 130 case '+': 131 *it = '-'; 132 break; 133 case '/': 134 *it = '_'; 135 break; 136 default: 137 break; 138 } 139 } 140 base::TrimString(result, "=", &result); 141 142 return result; 143 } 144 145 std::vector<uint8> UrlSafeB64Decode(const base::StringPiece& input) { 146 std::string unsafe(input.begin(), input.end()); 147 for (std::string::iterator it = unsafe.begin(); it != unsafe.end(); ++it) { 148 switch (*it) { 149 case '-': 150 *it = '+'; 151 break; 152 case '_': 153 *it = '/'; 154 break; 155 default: 156 break; 157 } 158 } 159 if (unsafe.length() % 4) 160 unsafe.append(4 - (unsafe.length() % 4), '='); 161 162 std::string decoded; 163 if (!base::Base64Decode(unsafe, &decoded)) 164 return std::vector<uint8>(); 165 166 return std::vector<uint8>(decoded.begin(), decoded.end()); 167 } 168 169 } // end namespace 170 171 ClientUpdateProtocol::ClientUpdateProtocol(int key_version) 172 : pub_key_version_(key_version) { 173 } 174 175 scoped_ptr<ClientUpdateProtocol> ClientUpdateProtocol::Create( 176 int key_version, 177 const base::StringPiece& public_key) { 178 DCHECK_GT(key_version, 0); 179 DCHECK(!public_key.empty()); 180 181 scoped_ptr<ClientUpdateProtocol> result( 182 new ClientUpdateProtocol(key_version)); 183 if (!result) 184 return scoped_ptr<ClientUpdateProtocol>(); 185 186 if (!result->LoadPublicKey(public_key)) 187 return scoped_ptr<ClientUpdateProtocol>(); 188 189 if (!result->BuildRandomSharedKey()) 190 return scoped_ptr<ClientUpdateProtocol>(); 191 192 return result.Pass(); 193 } 194 195 std::string ClientUpdateProtocol::GetVersionedSecret() const { 196 return base::StringPrintf("%d:%s", 197 pub_key_version_, 198 UrlSafeB64Encode(encrypted_key_source_).c_str()); 199 } 200 201 bool ClientUpdateProtocol::SignRequest(const base::StringPiece& url, 202 const base::StringPiece& request_body, 203 std::string* client_proof) { 204 DCHECK(!encrypted_key_source_.empty()); 205 DCHECK(!url.empty()); 206 DCHECK(!request_body.empty()); 207 DCHECK(client_proof); 208 209 // Compute the challenge hash: 210 // hw = HASH(HASH(v|w)|HASH(request_url)|HASH(body)). 211 // Keep the challenge hash for later to validate the server's response. 212 std::vector<uint8> internal_hashes; 213 214 std::vector<uint8> h; 215 h = Hash(GetVersionedSecret()); 216 internal_hashes.insert(internal_hashes.end(), h.begin(), h.end()); 217 h = Hash(url); 218 internal_hashes.insert(internal_hashes.end(), h.begin(), h.end()); 219 h = Hash(request_body); 220 internal_hashes.insert(internal_hashes.end(), h.begin(), h.end()); 221 DCHECK_EQ(internal_hashes.size(), 3 * HashDigestSize()); 222 223 client_challenge_hash_ = Hash(internal_hashes); 224 225 // Sign the challenge hash (hw) using the shared key (sk) to produce the 226 // client proof (cp). 227 std::vector<uint8> raw_client_proof = 228 SymSign(shared_key_, SymConcat(3, &client_challenge_hash_, NULL, NULL)); 229 if (raw_client_proof.empty()) { 230 client_challenge_hash_.clear(); 231 return false; 232 } 233 234 *client_proof = UrlSafeB64Encode(raw_client_proof); 235 return true; 236 } 237 238 bool ClientUpdateProtocol::ValidateResponse( 239 const base::StringPiece& response_body, 240 const base::StringPiece& server_cookie, 241 const base::StringPiece& server_proof) { 242 DCHECK(!client_challenge_hash_.empty()); 243 244 if (response_body.empty() || server_cookie.empty() || server_proof.empty()) 245 return false; 246 247 // Decode the server proof from URL-safe Base64 to a binary HMAC for the 248 // response. 249 std::vector<uint8> sp_decoded = UrlSafeB64Decode(server_proof); 250 if (sp_decoded.empty()) 251 return false; 252 253 // If the request was received by the server, the server will use its 254 // private key to decrypt |w_|, yielding the original contents of |r_|. 255 // The server can then recreate |sk_|, compute |hw_|, and SymSign(3|hw) 256 // to ensure that the cp matches the contents. It will then use |sk_| 257 // to sign its response, producing the server proof |sp|. 258 std::vector<uint8> hm = Hash(response_body); 259 std::vector<uint8> hc = Hash(server_cookie); 260 return SymSignVerify(shared_key_, 261 SymConcat(1, &client_challenge_hash_, &hm, &hc), 262 sp_decoded); 263 } 264 265 bool ClientUpdateProtocol::BuildRandomSharedKey() { 266 DCHECK_GE(PublicKeyLength(), HashDigestSize()); 267 268 // Start by generating some random bytes that are suitable to be encrypted; 269 // this will be the source of the shared HMAC key that client and server use. 270 // (CUP specification calls this "r".) 271 std::vector<uint8> key_source; 272 std::vector<uint8> entropy(PublicKeyLength() - HashDigestSize()); 273 crypto::RandBytes(&entropy[0], entropy.size()); 274 key_source = RsaPad(PublicKeyLength(), entropy); 275 276 return DeriveSharedKey(key_source); 277 } 278 279 bool ClientUpdateProtocol::SetSharedKeyForTesting( 280 const base::StringPiece& key_source) { 281 DCHECK_EQ(key_source.length(), PublicKeyLength()); 282 283 return DeriveSharedKey(std::vector<uint8>(key_source.begin(), 284 key_source.end())); 285 } 286 287 bool ClientUpdateProtocol::DeriveSharedKey(const std::vector<uint8>& source) { 288 DCHECK(!source.empty()); 289 DCHECK_GE(source.size(), HashDigestSize()); 290 DCHECK_EQ(source.size(), PublicKeyLength()); 291 292 // Hash the key source (r) to generate a new shared HMAC key (sk'). 293 shared_key_ = Hash(source); 294 295 // Encrypt the key source (r) using the public key (pk[v]) to generate the 296 // encrypted key source (w). 297 if (!EncryptKeySource(source)) 298 return false; 299 if (encrypted_key_source_.size() != PublicKeyLength()) 300 return false; 301 302 return true; 303 } 304
