// Copyright 2017 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package tls import ( "bytes" "crypto" "crypto/ecdsa" "crypto/ed25519" "crypto/elliptic" "crypto/rsa" "errors" "fmt" "hash" "io" ) // verifyHandshakeSignature verifies a signature against pre-hashed // (if required) handshake contents. func verifyHandshakeSignature(sigType uint8, pubkey crypto.PublicKey, hashFunc crypto.Hash, signed, sig []byte) error { switch sigType { case signatureECDSA: pubKey, ok := pubkey.(*ecdsa.PublicKey) if !ok { return fmt.Errorf("expected an ECDSA public key, got %T", pubkey) } if !ecdsa.VerifyASN1(pubKey, signed, sig) { return errors.New("ECDSA verification failure") } case signatureEd25519: pubKey, ok := pubkey.(ed25519.PublicKey) if !ok { return fmt.Errorf("expected an Ed25519 public key, got %T", pubkey) } if !ed25519.Verify(pubKey, signed, sig) { return errors.New("Ed25519 verification failure") } case signaturePKCS1v15: pubKey, ok := pubkey.(*rsa.PublicKey) if !ok { return fmt.Errorf("expected an RSA public key, got %T", pubkey) } if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, signed, sig); err != nil { return err } case signatureRSAPSS: pubKey, ok := pubkey.(*rsa.PublicKey) if !ok { return fmt.Errorf("expected an RSA public key, got %T", pubkey) } signOpts := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash} if err := rsa.VerifyPSS(pubKey, hashFunc, signed, sig, signOpts); err != nil { return err } default: return errors.New("internal error: unknown signature type") } return nil } const ( serverSignatureContext = "TLS 1.3, server CertificateVerify\x00" clientSignatureContext = "TLS 1.3, client CertificateVerify\x00" ) var signaturePadding = []byte{ 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, } // signedMessage returns the pre-hashed (if necessary) message to be signed by // certificate keys in TLS 1.3. See RFC 8446, Section 4.4.3. func signedMessage(sigHash crypto.Hash, context string, transcript hash.Hash) []byte { if sigHash == directSigning { b := &bytes.Buffer{} b.Write(signaturePadding) io.WriteString(b, context) b.Write(transcript.Sum(nil)) return b.Bytes() } h := sigHash.New() h.Write(signaturePadding) io.WriteString(h, context) h.Write(transcript.Sum(nil)) return h.Sum(nil) } // typeAndHashFromSignatureScheme returns the corresponding signature type and // crypto.Hash for a given TLS SignatureScheme. func typeAndHashFromSignatureScheme(signatureAlgorithm SignatureScheme) (sigType uint8, hash crypto.Hash, err error) { switch signatureAlgorithm { case PKCS1WithSHA1, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512: sigType = signaturePKCS1v15 case PSSWithSHA256, PSSWithSHA384, PSSWithSHA512: sigType = signatureRSAPSS case ECDSAWithSHA1, ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512: sigType = signatureECDSA case Ed25519: sigType = signatureEd25519 default: return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm) } switch signatureAlgorithm { case PKCS1WithSHA1, ECDSAWithSHA1: hash = crypto.SHA1 case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256: hash = crypto.SHA256 case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384: hash = crypto.SHA384 case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512: hash = crypto.SHA512 case Ed25519: hash = directSigning default: return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm) } return sigType, hash, nil } // legacyTypeAndHashFromPublicKey returns the fixed signature type and crypto.Hash for // a given public key used with TLS 1.0 and 1.1, before the introduction of // signature algorithm negotiation. func legacyTypeAndHashFromPublicKey(pub crypto.PublicKey) (sigType uint8, hash crypto.Hash, err error) { switch pub.(type) { case *rsa.PublicKey: return signaturePKCS1v15, crypto.MD5SHA1, nil case *ecdsa.PublicKey: return signatureECDSA, crypto.SHA1, nil case ed25519.PublicKey: // RFC 8422 specifies support for Ed25519 in TLS 1.0 and 1.1, // but it requires holding on to a handshake transcript to do a // full signature, and not even OpenSSL bothers with the // complexity, so we can't even test it properly. return 0, 0, fmt.Errorf("tls: Ed25519 public keys are not supported before TLS 1.2") default: return 0, 0, fmt.Errorf("tls: unsupported public key: %T", pub) } } var rsaSignatureSchemes = []struct { scheme SignatureScheme minModulusBytes int maxVersion uint16 }{ // RSA-PSS is used with PSSSaltLengthEqualsHash, and requires // emLen >= hLen + sLen + 2 {PSSWithSHA256, crypto.SHA256.Size()*2 + 2, VersionTLS13}, {PSSWithSHA384, crypto.SHA384.Size()*2 + 2, VersionTLS13}, {PSSWithSHA512, crypto.SHA512.Size()*2 + 2, VersionTLS13}, // PKCS #1 v1.5 uses prefixes from hashPrefixes in crypto/rsa, and requires // emLen >= len(prefix) + hLen + 11 // TLS 1.3 dropped support for PKCS #1 v1.5 in favor of RSA-PSS. {PKCS1WithSHA256, 19 + crypto.SHA256.Size() + 11, VersionTLS12}, {PKCS1WithSHA384, 19 + crypto.SHA384.Size() + 11, VersionTLS12}, {PKCS1WithSHA512, 19 + crypto.SHA512.Size() + 11, VersionTLS12}, {PKCS1WithSHA1, 15 + crypto.SHA1.Size() + 11, VersionTLS12}, } // signatureSchemesForCertificate returns the list of supported SignatureSchemes // for a given certificate, based on the public key and the protocol version, // and optionally filtered by its explicit SupportedSignatureAlgorithms. // // This function must be kept in sync with supportedSignatureAlgorithms. func signatureSchemesForCertificate(version uint16, cert *Certificate) []SignatureScheme { priv, ok := cert.PrivateKey.(crypto.Signer) if !ok { return nil } var sigAlgs []SignatureScheme switch pub := priv.Public().(type) { case *ecdsa.PublicKey: if version != VersionTLS13 { // In TLS 1.2 and earlier, ECDSA algorithms are not // constrained to a single curve. sigAlgs = []SignatureScheme{ ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, ECDSAWithSHA1, } break } switch pub.Curve { case elliptic.P256(): sigAlgs = []SignatureScheme{ECDSAWithP256AndSHA256} case elliptic.P384(): sigAlgs = []SignatureScheme{ECDSAWithP384AndSHA384} case elliptic.P521(): sigAlgs = []SignatureScheme{ECDSAWithP521AndSHA512} default: return nil } case *rsa.PublicKey: size := pub.Size() sigAlgs = make([]SignatureScheme, 0, len(rsaSignatureSchemes)) for _, candidate := range rsaSignatureSchemes { if size >= candidate.minModulusBytes && version <= candidate.maxVersion { sigAlgs = append(sigAlgs, candidate.scheme) } } case ed25519.PublicKey: sigAlgs = []SignatureScheme{Ed25519} default: return nil } if cert.SupportedSignatureAlgorithms != nil { var filteredSigAlgs []SignatureScheme for _, sigAlg := range sigAlgs { if isSupportedSignatureAlgorithm(sigAlg, cert.SupportedSignatureAlgorithms) { filteredSigAlgs = append(filteredSigAlgs, sigAlg) } } return filteredSigAlgs } return sigAlgs } // selectSignatureScheme picks a SignatureScheme from the peer's preference list // that works with the selected certificate. It's only called for protocol // versions that support signature algorithms, so TLS 1.2 and 1.3. func selectSignatureScheme(vers uint16, c *Certificate, peerAlgs []SignatureScheme) (SignatureScheme, error) { supportedAlgs := signatureSchemesForCertificate(vers, c) if len(supportedAlgs) == 0 { return 0, unsupportedCertificateError(c) } if len(peerAlgs) == 0 && vers == VersionTLS12 { // For TLS 1.2, if the client didn't send signature_algorithms then we // can assume that it supports SHA1. See RFC 5246, Section 7.4.1.4.1. peerAlgs = []SignatureScheme{PKCS1WithSHA1, ECDSAWithSHA1} } // Pick signature scheme in the peer's preference order, as our // preference order is not configurable. for _, preferredAlg := range peerAlgs { if isSupportedSignatureAlgorithm(preferredAlg, supportedAlgs) { return preferredAlg, nil } } return 0, errors.New("tls: peer doesn't support any of the certificate's signature algorithms") } // unsupportedCertificateError returns a helpful error for certificates with // an unsupported private key. func unsupportedCertificateError(cert *Certificate) error { switch cert.PrivateKey.(type) { case rsa.PrivateKey, ecdsa.PrivateKey: return fmt.Errorf("tls: unsupported certificate: private key is %T, expected *%T", cert.PrivateKey, cert.PrivateKey) case *ed25519.PrivateKey: return fmt.Errorf("tls: unsupported certificate: private key is *ed25519.PrivateKey, expected ed25519.PrivateKey") } signer, ok := cert.PrivateKey.(crypto.Signer) if !ok { return fmt.Errorf("tls: certificate private key (%T) does not implement crypto.Signer", cert.PrivateKey) } switch pub := signer.Public().(type) { case *ecdsa.PublicKey: switch pub.Curve { case elliptic.P256(): case elliptic.P384(): case elliptic.P521(): default: return fmt.Errorf("tls: unsupported certificate curve (%s)", pub.Curve.Params().Name) } case *rsa.PublicKey: return fmt.Errorf("tls: certificate RSA key size too small for supported signature algorithms") case ed25519.PublicKey: default: return fmt.Errorf("tls: unsupported certificate key (%T)", pub) } if cert.SupportedSignatureAlgorithms != nil { return fmt.Errorf("tls: peer doesn't support the certificate custom signature algorithms") } return fmt.Errorf("tls: internal error: unsupported key (%T)", cert.PrivateKey) }