auth.go

     1  // Copyright 2017 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  	"bytes"
     9  	"crypto"
    10  	"crypto/ecdsa"
    11  	"crypto/ed25519"
    12  	"crypto/elliptic"
    13  	"crypto/rsa"
    14  	"errors"
    15  	"fmt"
    16  	"hash"
    17  	"io"
    18  )
    19  
    20  // verifyHandshakeSignature verifies a signature against pre-hashed
    21  // (if required) handshake contents.
    22  func verifyHandshakeSignature(sigType uint8, pubkey crypto.PublicKey, hashFunc crypto.Hash, signed, sig []byte) error {
    23  	switch sigType {
    24  	case signatureECDSA:
    25  		pubKey, ok := pubkey.(*ecdsa.PublicKey)
    26  		if !ok {
    27  			return fmt.Errorf("expected an ECDSA public key, got %T", pubkey)
    28  		}
    29  		if !ecdsa.VerifyASN1(pubKey, signed, sig) {
    30  			return errors.New("ECDSA verification failure")
    31  		}
    32  	case signatureEd25519:
    33  		pubKey, ok := pubkey.(ed25519.PublicKey)
    34  		if !ok {
    35  			return fmt.Errorf("expected an Ed25519 public key, got %T", pubkey)
    36  		}
    37  		if !ed25519.Verify(pubKey, signed, sig) {
    38  			return errors.New("Ed25519 verification failure")
    39  		}
    40  	case signaturePKCS1v15:
    41  		pubKey, ok := pubkey.(*rsa.PublicKey)
    42  		if !ok {
    43  			return fmt.Errorf("expected an RSA public key, got %T", pubkey)
    44  		}
    45  		if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, signed, sig); err != nil {
    46  			return err
    47  		}
    48  	case signatureRSAPSS:
    49  		pubKey, ok := pubkey.(*rsa.PublicKey)
    50  		if !ok {
    51  			return fmt.Errorf("expected an RSA public key, got %T", pubkey)
    52  		}
    53  		signOpts := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash}
    54  		if err := rsa.VerifyPSS(pubKey, hashFunc, signed, sig, signOpts); err != nil {
    55  			return err
    56  		}
    57  	default:
    58  		return errors.New("internal error: unknown signature type")
    59  	}
    60  	return nil
    61  }
    62  
    63  const (
    64  	serverSignatureContext = "TLS 1.3, server CertificateVerify\x00"
    65  	clientSignatureContext = "TLS 1.3, client CertificateVerify\x00"
    66  )
    67  
    68  var signaturePadding = []byte{
    69  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    70  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    71  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    72  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    73  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    74  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    75  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    76  	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
    77  }
    78  
    79  // signedMessage returns the pre-hashed (if necessary) message to be signed by
    80  // certificate keys in TLS 1.3. See RFC 8446, Section 4.4.3.
    81  func signedMessage(sigHash crypto.Hash, context string, transcript hash.Hash) []byte {
    82  	if sigHash == directSigning {
    83  		b := &bytes.Buffer{}
    84  		b.Write(signaturePadding)
    85  		io.WriteString(b, context)
    86  		b.Write(transcript.Sum(nil))
    87  		return b.Bytes()
    88  	}
    89  	h := sigHash.New()
    90  	h.Write(signaturePadding)
    91  	io.WriteString(h, context)
    92  	h.Write(transcript.Sum(nil))
    93  	return h.Sum(nil)
    94  }
    95  
    96  // typeAndHashFromSignatureScheme returns the corresponding signature type and
    97  // crypto.Hash for a given TLS SignatureScheme.
    98  func typeAndHashFromSignatureScheme(signatureAlgorithm SignatureScheme) (sigType uint8, hash crypto.Hash, err error) {
    99  	switch signatureAlgorithm {
   100  	case PKCS1WithSHA1, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512:
   101  		sigType = signaturePKCS1v15
   102  	case PSSWithSHA256, PSSWithSHA384, PSSWithSHA512:
   103  		sigType = signatureRSAPSS
   104  	case ECDSAWithSHA1, ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512:
   105  		sigType = signatureECDSA
   106  	case Ed25519:
   107  		sigType = signatureEd25519
   108  	default:
   109  		return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm)
   110  	}
   111  	switch signatureAlgorithm {
   112  	case PKCS1WithSHA1, ECDSAWithSHA1:
   113  		hash = crypto.SHA1
   114  	case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
   115  		hash = crypto.SHA256
   116  	case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
   117  		hash = crypto.SHA384
   118  	case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
   119  		hash = crypto.SHA512
   120  	case Ed25519:
   121  		hash = directSigning
   122  	default:
   123  		return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm)
   124  	}
   125  	return sigType, hash, nil
   126  }
   127  
   128  // legacyTypeAndHashFromPublicKey returns the fixed signature type and crypto.Hash for
   129  // a given public key used with TLS 1.0 and 1.1, before the introduction of
   130  // signature algorithm negotiation.
   131  func legacyTypeAndHashFromPublicKey(pub crypto.PublicKey) (sigType uint8, hash crypto.Hash, err error) {
   132  	switch pub.(type) {
   133  	case *rsa.PublicKey:
   134  		return signaturePKCS1v15, crypto.MD5SHA1, nil
   135  	case *ecdsa.PublicKey:
   136  		return signatureECDSA, crypto.SHA1, nil
   137  	case ed25519.PublicKey:
   138  		// RFC 8422 specifies support for Ed25519 in TLS 1.0 and 1.1,
   139  		// but it requires holding on to a handshake transcript to do a
   140  		// full signature, and not even OpenSSL bothers with the
   141  		// complexity, so we can't even test it properly.
   142  		return 0, 0, fmt.Errorf("tls: Ed25519 public keys are not supported before TLS 1.2")
   143  	default:
   144  		return 0, 0, fmt.Errorf("tls: unsupported public key: %T", pub)
   145  	}
   146  }
   147  
   148  var rsaSignatureSchemes = []struct {
   149  	scheme          SignatureScheme
   150  	minModulusBytes int
   151  	maxVersion      uint16
   152  }{
   153  	// RSA-PSS is used with PSSSaltLengthEqualsHash, and requires
   154  	//    emLen >= hLen + sLen + 2
   155  	{PSSWithSHA256, crypto.SHA256.Size()*2 + 2, VersionTLS13},
   156  	{PSSWithSHA384, crypto.SHA384.Size()*2 + 2, VersionTLS13},
   157  	{PSSWithSHA512, crypto.SHA512.Size()*2 + 2, VersionTLS13},
   158  	// PKCS #1 v1.5 uses prefixes from hashPrefixes in crypto/rsa, and requires
   159  	//    emLen >= len(prefix) + hLen + 11
   160  	// TLS 1.3 dropped support for PKCS #1 v1.5 in favor of RSA-PSS.
   161  	{PKCS1WithSHA256, 19 + crypto.SHA256.Size() + 11, VersionTLS12},
   162  	{PKCS1WithSHA384, 19 + crypto.SHA384.Size() + 11, VersionTLS12},
   163  	{PKCS1WithSHA512, 19 + crypto.SHA512.Size() + 11, VersionTLS12},
   164  	{PKCS1WithSHA1, 15 + crypto.SHA1.Size() + 11, VersionTLS12},
   165  }
   166  
   167  // signatureSchemesForCertificate returns the list of supported SignatureSchemes
   168  // for a given certificate, based on the public key and the protocol version,
   169  // and optionally filtered by its explicit SupportedSignatureAlgorithms.
   170  //
   171  // This function must be kept in sync with supportedSignatureAlgorithms.
   172  // FIPS filtering is applied in the caller, selectSignatureScheme.
   173  func signatureSchemesForCertificate(version uint16, cert *Certificate) []SignatureScheme {
   174  	priv, ok := cert.PrivateKey.(crypto.Signer)
   175  	if !ok {
   176  		return nil
   177  	}
   178  
   179  	var sigAlgs []SignatureScheme
   180  	switch pub := priv.Public().(type) {
   181  	case *ecdsa.PublicKey:
   182  		if version != VersionTLS13 {
   183  			// In TLS 1.2 and earlier, ECDSA algorithms are not
   184  			// constrained to a single curve.
   185  			sigAlgs = []SignatureScheme{
   186  				ECDSAWithP256AndSHA256,
   187  				ECDSAWithP384AndSHA384,
   188  				ECDSAWithP521AndSHA512,
   189  				ECDSAWithSHA1,
   190  			}
   191  			break
   192  		}
   193  		switch pub.Curve {
   194  		case elliptic.P256():
   195  			sigAlgs = []SignatureScheme{ECDSAWithP256AndSHA256}
   196  		case elliptic.P384():
   197  			sigAlgs = []SignatureScheme{ECDSAWithP384AndSHA384}
   198  		case elliptic.P521():
   199  			sigAlgs = []SignatureScheme{ECDSAWithP521AndSHA512}
   200  		default:
   201  			return nil
   202  		}
   203  	case *rsa.PublicKey:
   204  		size := pub.Size()
   205  		sigAlgs = make([]SignatureScheme, 0, len(rsaSignatureSchemes))
   206  		for _, candidate := range rsaSignatureSchemes {
   207  			if size >= candidate.minModulusBytes && version <= candidate.maxVersion {
   208  				sigAlgs = append(sigAlgs, candidate.scheme)
   209  			}
   210  		}
   211  	case ed25519.PublicKey:
   212  		sigAlgs = []SignatureScheme{Ed25519}
   213  	default:
   214  		return nil
   215  	}
   216  
   217  	if cert.SupportedSignatureAlgorithms != nil {
   218  		var filteredSigAlgs []SignatureScheme
   219  		for _, sigAlg := range sigAlgs {
   220  			if isSupportedSignatureAlgorithm(sigAlg, cert.SupportedSignatureAlgorithms) {
   221  				filteredSigAlgs = append(filteredSigAlgs, sigAlg)
   222  			}
   223  		}
   224  		return filteredSigAlgs
   225  	}
   226  	return sigAlgs
   227  }
   228  
   229  // selectSignatureScheme picks a SignatureScheme from the peer's preference list
   230  // that works with the selected certificate. It's only called for protocol
   231  // versions that support signature algorithms, so TLS 1.2 and 1.3.
   232  func selectSignatureScheme(vers uint16, c *Certificate, peerAlgs []SignatureScheme) (SignatureScheme, error) {
   233  	supportedAlgs := signatureSchemesForCertificate(vers, c)
   234  	if len(supportedAlgs) == 0 {
   235  		return 0, unsupportedCertificateError(c)
   236  	}
   237  	if len(peerAlgs) == 0 && vers == VersionTLS12 {
   238  		// For TLS 1.2, if the client didn't send signature_algorithms then we
   239  		// can assume that it supports SHA1. See RFC 5246, Section 7.4.1.4.1.
   240  		peerAlgs = []SignatureScheme{PKCS1WithSHA1, ECDSAWithSHA1}
   241  	}
   242  	// Pick signature scheme in the peer's preference order, as our
   243  	// preference order is not configurable.
   244  	for _, preferredAlg := range peerAlgs {
   245  		if needFIPS() && !isSupportedSignatureAlgorithm(preferredAlg, defaultSupportedSignatureAlgorithmsFIPS) {
   246  			continue
   247  		}
   248  		if isSupportedSignatureAlgorithm(preferredAlg, supportedAlgs) {
   249  			return preferredAlg, nil
   250  		}
   251  	}
   252  	return 0, errors.New("tls: peer doesn't support any of the certificate's signature algorithms")
   253  }
   254  
   255  // unsupportedCertificateError returns a helpful error for certificates with
   256  // an unsupported private key.
   257  func unsupportedCertificateError(cert *Certificate) error {
   258  	switch cert.PrivateKey.(type) {
   259  	case rsa.PrivateKey, ecdsa.PrivateKey:
   260  		return fmt.Errorf("tls: unsupported certificate: private key is %T, expected *%T",
   261  			cert.PrivateKey, cert.PrivateKey)
   262  	case *ed25519.PrivateKey:
   263  		return fmt.Errorf("tls: unsupported certificate: private key is *ed25519.PrivateKey, expected ed25519.PrivateKey")
   264  	}
   265  
   266  	signer, ok := cert.PrivateKey.(crypto.Signer)
   267  	if !ok {
   268  		return fmt.Errorf("tls: certificate private key (%T) does not implement crypto.Signer",
   269  			cert.PrivateKey)
   270  	}
   271  
   272  	switch pub := signer.Public().(type) {
   273  	case *ecdsa.PublicKey:
   274  		switch pub.Curve {
   275  		case elliptic.P256():
   276  		case elliptic.P384():
   277  		case elliptic.P521():
   278  		default:
   279  			return fmt.Errorf("tls: unsupported certificate curve (%s)", pub.Curve.Params().Name)
   280  		}
   281  	case *rsa.PublicKey:
   282  		return fmt.Errorf("tls: certificate RSA key size too small for supported signature algorithms")
   283  	case ed25519.PublicKey:
   284  	default:
   285  		return fmt.Errorf("tls: unsupported certificate key (%T)", pub)
   286  	}
   287  
   288  	if cert.SupportedSignatureAlgorithms != nil {
   289  		return fmt.Errorf("tls: peer doesn't support the certificate custom signature algorithms")
   290  	}
   291  
   292  	return fmt.Errorf("tls: internal error: unsupported key (%T)", cert.PrivateKey)
   293  }
   294
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