github.com/icodeface/tls@v0.0.0-20230910023335-34df9250cd12/key_agreement.go (about) 1 // Copyright 2010 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package tls 6 7 import ( 8 "crypto" 9 "crypto/md5" 10 "crypto/rsa" 11 "crypto/sha1" 12 "crypto/x509" 13 "errors" 14 "io" 15 ) 16 17 var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message") 18 var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message") 19 20 // rsaKeyAgreement implements the standard TLS key agreement where the client 21 // encrypts the pre-master secret to the server's public key. 22 type rsaKeyAgreement struct{} 23 24 func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) { 25 return nil, nil 26 } 27 28 func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) { 29 if len(ckx.ciphertext) < 2 { 30 return nil, errClientKeyExchange 31 } 32 33 ciphertext := ckx.ciphertext 34 if version != VersionSSL30 { 35 ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1]) 36 if ciphertextLen != len(ckx.ciphertext)-2 { 37 return nil, errClientKeyExchange 38 } 39 ciphertext = ckx.ciphertext[2:] 40 } 41 priv, ok := cert.PrivateKey.(crypto.Decrypter) 42 if !ok { 43 return nil, errors.New("tls: certificate private key does not implement crypto.Decrypter") 44 } 45 // Perform constant time RSA PKCS#1 v1.5 decryption 46 preMasterSecret, err := priv.Decrypt(config.rand(), ciphertext, &rsa.PKCS1v15DecryptOptions{SessionKeyLen: 48}) 47 if err != nil { 48 return nil, err 49 } 50 // We don't check the version number in the premaster secret. For one, 51 // by checking it, we would leak information about the validity of the 52 // encrypted pre-master secret. Secondly, it provides only a small 53 // benefit against a downgrade attack and some implementations send the 54 // wrong version anyway. See the discussion at the end of section 55 // 7.4.7.1 of RFC 4346. 56 return preMasterSecret, nil 57 } 58 59 func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error { 60 return errors.New("tls: unexpected ServerKeyExchange") 61 } 62 63 func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) { 64 preMasterSecret := make([]byte, 48) 65 preMasterSecret[0] = byte(clientHello.vers >> 8) 66 preMasterSecret[1] = byte(clientHello.vers) 67 _, err := io.ReadFull(config.rand(), preMasterSecret[2:]) 68 if err != nil { 69 return nil, nil, err 70 } 71 72 encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret) 73 if err != nil { 74 return nil, nil, err 75 } 76 ckx := new(clientKeyExchangeMsg) 77 ckx.ciphertext = make([]byte, len(encrypted)+2) 78 ckx.ciphertext[0] = byte(len(encrypted) >> 8) 79 ckx.ciphertext[1] = byte(len(encrypted)) 80 copy(ckx.ciphertext[2:], encrypted) 81 return preMasterSecret, ckx, nil 82 } 83 84 // sha1Hash calculates a SHA1 hash over the given byte slices. 85 func sha1Hash(slices [][]byte) []byte { 86 hsha1 := sha1.New() 87 for _, slice := range slices { 88 hsha1.Write(slice) 89 } 90 return hsha1.Sum(nil) 91 } 92 93 // md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the 94 // concatenation of an MD5 and SHA1 hash. 95 func md5SHA1Hash(slices [][]byte) []byte { 96 md5sha1 := make([]byte, md5.Size+sha1.Size) 97 hmd5 := md5.New() 98 for _, slice := range slices { 99 hmd5.Write(slice) 100 } 101 copy(md5sha1, hmd5.Sum(nil)) 102 copy(md5sha1[md5.Size:], sha1Hash(slices)) 103 return md5sha1 104 } 105 106 // hashForServerKeyExchange hashes the given slices and returns their digest 107 // using the given hash function (for >= TLS 1.2) or using a default based on 108 // the sigType (for earlier TLS versions). 109 func hashForServerKeyExchange(sigType uint8, hashFunc crypto.Hash, version uint16, slices ...[]byte) ([]byte, error) { 110 if version >= VersionTLS12 { 111 h := hashFunc.New() 112 for _, slice := range slices { 113 h.Write(slice) 114 } 115 digest := h.Sum(nil) 116 return digest, nil 117 } 118 if sigType == signatureECDSA { 119 return sha1Hash(slices), nil 120 } 121 return md5SHA1Hash(slices), nil 122 } 123 124 // ecdheKeyAgreement implements a TLS key agreement where the server 125 // generates an ephemeral EC public/private key pair and signs it. The 126 // pre-master secret is then calculated using ECDH. The signature may 127 // either be ECDSA or RSA. 128 type ecdheKeyAgreement struct { 129 version uint16 130 isRSA bool 131 params ecdheParameters 132 133 // ckx and preMasterSecret are generated in processServerKeyExchange 134 // and returned in generateClientKeyExchange. 135 ckx *clientKeyExchangeMsg 136 preMasterSecret []byte 137 } 138 139 func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) { 140 preferredCurves := config.curvePreferences() 141 142 var curveID CurveID 143 NextCandidate: 144 for _, candidate := range preferredCurves { 145 for _, c := range clientHello.supportedCurves { 146 if candidate == c { 147 curveID = c 148 break NextCandidate 149 } 150 } 151 } 152 153 if curveID == 0 { 154 return nil, errors.New("tls: no supported elliptic curves offered") 155 } 156 if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok { 157 return nil, errors.New("tls: CurvePreferences includes unsupported curve") 158 } 159 160 params, err := generateECDHEParameters(config.rand(), curveID) 161 if err != nil { 162 return nil, err 163 } 164 ka.params = params 165 166 // See RFC 4492, Section 5.4. 167 ecdhePublic := params.PublicKey() 168 serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic)) 169 serverECDHParams[0] = 3 // named curve 170 serverECDHParams[1] = byte(curveID >> 8) 171 serverECDHParams[2] = byte(curveID) 172 serverECDHParams[3] = byte(len(ecdhePublic)) 173 copy(serverECDHParams[4:], ecdhePublic) 174 175 priv, ok := cert.PrivateKey.(crypto.Signer) 176 if !ok { 177 return nil, errors.New("tls: certificate private key does not implement crypto.Signer") 178 } 179 180 signatureAlgorithm, sigType, hashFunc, err := pickSignatureAlgorithm(priv.Public(), clientHello.supportedSignatureAlgorithms, supportedSignatureAlgorithmsTLS12, ka.version) 181 if err != nil { 182 return nil, err 183 } 184 if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA { 185 return nil, errors.New("tls: certificate cannot be used with the selected cipher suite") 186 } 187 188 digest, err := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, hello.random, serverECDHParams) 189 if err != nil { 190 return nil, err 191 } 192 193 signOpts := crypto.SignerOpts(hashFunc) 194 if sigType == signatureRSAPSS { 195 signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: hashFunc} 196 } 197 sig, err := priv.Sign(config.rand(), digest, signOpts) 198 if err != nil { 199 return nil, errors.New("tls: failed to sign ECDHE parameters: " + err.Error()) 200 } 201 202 skx := new(serverKeyExchangeMsg) 203 sigAndHashLen := 0 204 if ka.version >= VersionTLS12 { 205 sigAndHashLen = 2 206 } 207 skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig)) 208 copy(skx.key, serverECDHParams) 209 k := skx.key[len(serverECDHParams):] 210 if ka.version >= VersionTLS12 { 211 k[0] = byte(signatureAlgorithm >> 8) 212 k[1] = byte(signatureAlgorithm) 213 k = k[2:] 214 } 215 k[0] = byte(len(sig) >> 8) 216 k[1] = byte(len(sig)) 217 copy(k[2:], sig) 218 219 return skx, nil 220 } 221 222 func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) { 223 if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 { 224 return nil, errClientKeyExchange 225 } 226 227 preMasterSecret := ka.params.SharedKey(ckx.ciphertext[1:]) 228 if preMasterSecret == nil { 229 return nil, errClientKeyExchange 230 } 231 232 return preMasterSecret, nil 233 } 234 235 func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error { 236 if len(skx.key) < 4 { 237 return errServerKeyExchange 238 } 239 if skx.key[0] != 3 { // named curve 240 return errors.New("tls: server selected unsupported curve") 241 } 242 curveID := CurveID(skx.key[1])<<8 | CurveID(skx.key[2]) 243 244 publicLen := int(skx.key[3]) 245 if publicLen+4 > len(skx.key) { 246 return errServerKeyExchange 247 } 248 serverECDHParams := skx.key[:4+publicLen] 249 publicKey := serverECDHParams[4:] 250 251 sig := skx.key[4+publicLen:] 252 if len(sig) < 2 { 253 return errServerKeyExchange 254 } 255 256 if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok { 257 return errors.New("tls: server selected unsupported curve") 258 } 259 260 params, err := generateECDHEParameters(config.rand(), curveID) 261 if err != nil { 262 return err 263 } 264 ka.params = params 265 266 ka.preMasterSecret = params.SharedKey(publicKey) 267 if ka.preMasterSecret == nil { 268 return errServerKeyExchange 269 } 270 271 ourPublicKey := params.PublicKey() 272 ka.ckx = new(clientKeyExchangeMsg) 273 ka.ckx.ciphertext = make([]byte, 1+len(ourPublicKey)) 274 ka.ckx.ciphertext[0] = byte(len(ourPublicKey)) 275 copy(ka.ckx.ciphertext[1:], ourPublicKey) 276 277 var signatureAlgorithm SignatureScheme 278 if ka.version >= VersionTLS12 { 279 // handle SignatureAndHashAlgorithm 280 signatureAlgorithm = SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1]) 281 sig = sig[2:] 282 if len(sig) < 2 { 283 return errServerKeyExchange 284 } 285 } 286 _, sigType, hashFunc, err := pickSignatureAlgorithm(cert.PublicKey, []SignatureScheme{signatureAlgorithm}, clientHello.supportedSignatureAlgorithms, ka.version) 287 if err != nil { 288 return err 289 } 290 if (sigType == signaturePKCS1v15 || sigType == signatureRSAPSS) != ka.isRSA { 291 return errServerKeyExchange 292 } 293 294 sigLen := int(sig[0])<<8 | int(sig[1]) 295 if sigLen+2 != len(sig) { 296 return errServerKeyExchange 297 } 298 sig = sig[2:] 299 300 digest, err := hashForServerKeyExchange(sigType, hashFunc, ka.version, clientHello.random, serverHello.random, serverECDHParams) 301 if err != nil { 302 return err 303 } 304 return verifyHandshakeSignature(sigType, cert.PublicKey, hashFunc, digest, sig) 305 } 306 307 func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) { 308 if ka.ckx == nil { 309 return nil, nil, errors.New("tls: missing ServerKeyExchange message") 310 } 311 312 return ka.preMasterSecret, ka.ckx, nil 313 }