Fix DC implementation #131

Addresses issues #127, #128, #129, and #130.
Add tool for generating delegated credentials.

Author: jhoyla

src/crypto/tls/auth.go

@@ -259,72 +259,26 @@ func signatureSchemesForCertificate(version uint16, cert *Certificate) []Signatu
 	return sigAlgs
 }
 
-// signatureSchemeForDelegatedCredential returns the list of supported
-// SignatureSchemes for a given delegated credential, based on the public
-// key, and optionally filtered by its explicit
-// SupportedSignatureAlgorithmsDC.
-//
-// This function must be kept in sync with supportedSignatureAlgorithmsDC.
-func signatureSchemeForDelegatedCredential(version uint16, dc *DelegatedCredential) []SignatureScheme {
-	pub := dc.cred.publicKey
-
-	var sigAlgs []SignatureScheme
-	switch pub.(type) {
-	case *ecdsa.PublicKey:
-		pk, ok := pub.(*ecdsa.PublicKey)
-		if !ok {
-			return nil
-		}
-		switch pk.Curve {
-		case elliptic.P256():
-			sigAlgs = []SignatureScheme{ECDSAWithP256AndSHA256}
-		case elliptic.P384():
-			sigAlgs = []SignatureScheme{ECDSAWithP384AndSHA384}
-		case elliptic.P521():
-			sigAlgs = []SignatureScheme{ECDSAWithP521AndSHA512}
-		default:
-			return nil
-		}
-	case ed25519.PublicKey:
-		sigAlgs = []SignatureScheme{Ed25519}
-	case circlSign.PublicKey:
-		pk, ok := pub.(circlSign.PublicKey)
-		if !ok {
-			return nil
-		}
-		scheme := pk.Scheme()
-		tlsScheme, ok := scheme.(circlPki.TLSScheme)
-		if !ok {
-			return nil
-		}
-		sigAlgs = []SignatureScheme{SignatureScheme(tlsScheme.TLSIdentifier())}
-	default:
-		return nil
-	}
-
-	return sigAlgs
-}
-
 // selectSignatureSchemeDC picks a SignatureScheme from the peer's preference list
 // that works with the selected delegated credential. It's only called for protocol
 // versions that support delegated credential, so TLS 1.3.
-func selectSignatureSchemeDC(vers uint16, dc *DelegatedCredential, peerAlgs []SignatureScheme) (SignatureScheme, error) {
+func selectSignatureSchemeDC(vers uint16, dc *DelegatedCredential, peerAlgs []SignatureScheme, peerAlgsDC []SignatureScheme) (SignatureScheme, error) {
 	if vers != VersionTLS13 {
 		return 0, errors.New("unsupported TLS version for dc")
 	}
 
-	supportedAlgs := signatureSchemeForDelegatedCredential(vers, dc)
-	if len(supportedAlgs) == 0 {
-		return 0, errors.New("unsupported scheme for dc")
+	if !isSupportedSignatureAlgorithm(dc.algorithm, peerAlgs) {
+		return undefinedSignatureScheme, errors.New("tls: peer doesn't support the delegated credential's signature")
 	}
+
 	// Pick signature scheme in the peer's preference order, as our
 	// preference order is not configurable.
-	for _, preferredAlg := range peerAlgs {
-		if isSupportedSignatureAlgorithm(preferredAlg, supportedAlgs) {
+	for _, preferredAlg := range peerAlgsDC {
+		if preferredAlg == dc.cred.expCertVerfAlgo {
 			return preferredAlg, nil
 		}
 	}
-	return 0, errors.New("tls: peer doesn't support any of the delegated credential's signature algorithms")
+	return 0, errors.New("tls: peer doesn't support the delegated credential's signature algorithm")
 }
 
 // selectSignatureScheme picks a SignatureScheme from the peer's preference list

src/crypto/tls/delegated_credentials.go

@@ -21,6 +21,7 @@ import (
 	"crypto/ed25519"
 	"crypto/elliptic"
 	"crypto/rand"
+	"crypto/rsa"
 	"crypto/x509"
 	"encoding/binary"
 	"errors"
@@ -40,6 +41,10 @@ const (
 	dcMaxSignatureLen = (1 << 16) - 1 // Bytes
 )
 
+const (
+	undefinedSignatureScheme SignatureScheme = 0x0000
+)
+
 var extensionDelegatedCredential = []int{1, 3, 6, 1, 4, 1, 44363, 44}
 
 // isValidForDelegation returns true if a certificate can be used for Delegated
@@ -61,7 +66,6 @@ func isValidForDelegation(cert *x509.Certificate) bool {
 			return true
 		}
 	}
-
 	return false
 }
 
@@ -133,6 +137,7 @@ func (cred *credential) marshalPublicKeyInfo() ([]byte, error) {
 		}
 
 		return rawPub, nil
+
 	default:
 		return nil, fmt.Errorf("tls: unsupported signature scheme: 0x%04x", cred.expCertVerfAlgo)
 	}
@@ -228,6 +233,12 @@ func getHash(scheme SignatureScheme) crypto.Hash {
 		return crypto.SHA512
 	case Ed25519:
 		return directSigning
+	case PKCS1WithSHA256, PSSWithSHA256:
+		return crypto.SHA256
+	case PSSWithSHA384:
+		return crypto.SHA384
+	case PSSWithSHA512:
+		return crypto.SHA512
 	default:
 		return 0 //Unknown hash function
 	}
@@ -291,28 +302,29 @@ func prepareDelegationSignatureInput(hash crypto.Hash, cred *credential, dCert [
 // Extract the algorithm used to sign the Delegated Credential from the
 // end-entity (leaf) certificate.
 func getSignatureAlgorithm(cert *Certificate) (SignatureScheme, error) {
-	var sigAlgo SignatureScheme
 	switch sk := cert.PrivateKey.(type) {
 	case *ecdsa.PrivateKey:
 		pk := sk.Public().(*ecdsa.PublicKey)
 		curveName := pk.Curve.Params().Name
-		certAlg := cert.Leaf.SignatureAlgorithm
-		if certAlg == x509.ECDSAWithSHA256 && curveName == "P-256" {
-			sigAlgo = ECDSAWithP256AndSHA256
-		} else if certAlg == x509.ECDSAWithSHA384 && curveName == "P-384" {
-			sigAlgo = ECDSAWithP384AndSHA384
-		} else if certAlg == x509.ECDSAWithSHA512 && curveName == "P-521" {
-			sigAlgo = ECDSAWithP521AndSHA512
+		certAlg := cert.Leaf.PublicKeyAlgorithm
+		if certAlg == x509.ECDSA && curveName == "P-256" {
+			return ECDSAWithP256AndSHA256, nil
+		} else if certAlg == x509.ECDSA && curveName == "P-384" {
+			return ECDSAWithP384AndSHA384, nil
+		} else if certAlg == x509.ECDSA && curveName == "P-521" {
+			return ECDSAWithP521AndSHA512, nil
 		} else {
-			return SignatureScheme(0x00), fmt.Errorf("using curve %s for %s is not supported", curveName, cert.Leaf.SignatureAlgorithm)
+			return undefinedSignatureScheme, fmt.Errorf("using curve %s for %s is not supported", curveName, cert.Leaf.SignatureAlgorithm)
 		}
 	case ed25519.PrivateKey:
-		sigAlgo = Ed25519
+		return Ed25519, nil
+	case *rsa.PrivateKey:
+		// If the certificate has the RSAEncryption OID there are a number of valid signature schemes that may sign the DC.
+		// In the absence of better information, we make a reasonable choice.
+		return PSSWithSHA256, nil
 	default:
-		return SignatureScheme(0x00), fmt.Errorf("tls: unsupported algorithm for Delegated Credential")
+		return undefinedSignatureScheme, fmt.Errorf("tls: unsupported algorithm for signing Delegated Credential")
 	}
-
-	return sigAlgo, nil
 }
 
 // NewDelegatedCredential creates a new Delegated Credential using 'cert' for
@@ -365,7 +377,7 @@ func NewDelegatedCredential(cert *Certificate, pubAlgo SignatureScheme, validTim
 			return nil, nil, err
 		}
 	default:
-		return nil, nil, fmt.Errorf("tls: unsupported algorithm for Delegated Credential: %T", pubAlgo)
+		return nil, nil, fmt.Errorf("tls: unsupported algorithm for Delegated Credential: %s", pubAlgo)
 	}
 
 	// Prepare the credential for signing
@@ -390,6 +402,13 @@ func NewDelegatedCredential(cert *Certificate, pubAlgo SignatureScheme, validTim
 		if err != nil {
 			return nil, nil, err
 		}
+	case *rsa.PrivateKey:
+		opts := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash,
+			Hash: hash}
+		sig, err = rsa.SignPSS(rand.Reader, sk, hash, values, opts)
+		if err != nil {
+			return nil, nil, err
+		}
 	default:
 		return nil, nil, fmt.Errorf("tls: unsupported key type for Delegated Credential")
 	}
@@ -448,17 +467,29 @@ func (dc *DelegatedCredential) Validate(cert *x509.Certificate, isClient bool, n
 		}
 
 		return ed25519.Verify(pk, in, dc.signature)
+	case PSSWithSHA256,
+		PSSWithSHA384,
+		PSSWithSHA512:
+		pk, ok := cert.PublicKey.(*rsa.PublicKey)
+		if !ok {
+			return false
+		}
+		hash := getHash(dc.algorithm)
+		return rsa.VerifyPSS(pk, hash, in, dc.signature, nil) == nil
 	default:
 		return false
 	}
 }
 
-// marshal encodes a DelegatedCredential structure. It also sets dc.Raw to that
+// Marshal encodes a DelegatedCredential structure. It also sets dc.Raw to that
 // encoding.
-func (dc *DelegatedCredential) marshal() ([]byte, error) {
+func (dc *DelegatedCredential) Marshal() ([]byte, error) {
 	if len(dc.signature) > dcMaxSignatureLen {
 		return nil, errors.New("tls: delegated credential is not valid")
 	}
+	if len(dc.signature) == 0 {
+		return nil, errors.New("tls: delegated credential has no signature")
+	}
 
 	raw, err := dc.cred.marshal()
 	if err != nil {
@@ -475,8 +506,8 @@ func (dc *DelegatedCredential) marshal() ([]byte, error) {
 	return dc.raw, nil
 }
 
-// unmarshalDelegatedCredential decodes a DelegatedCredential structure.
-func unmarshalDelegatedCredential(raw []byte) (*DelegatedCredential, error) {
+// UnmarshalDelegatedCredential decodes a DelegatedCredential structure.
+func UnmarshalDelegatedCredential(raw []byte) (*DelegatedCredential, error) {
 	rawCredentialLen, err := getCredentialLen(raw)
 	if err != nil {
 		return nil, err

src/crypto/tls/delegated_credentials_test.go

@@ -385,12 +385,12 @@ func TestDelegatedCredentialMarshal(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		ser, err := delegatedCred.marshal()
+		ser, err := delegatedCred.Marshal()
 		if err != nil {
 			t.Error(err)
 		}
 
-		delegatedCred2, err := unmarshalDelegatedCredential(ser)
+		delegatedCred2, err := UnmarshalDelegatedCredential(ser)
 		if err != nil {
 			t.Error(err)
 		}
@@ -466,6 +466,12 @@ func testServerGetCertificate(ch *ClientHelloInfo) (*Certificate, error) {
 
 }
 
+// Used when the server doesn't support DCs.
+// This function always returns a non-DC cert.
+func testServerGetCertificateNoDC(ch *ClientHelloInfo) (*Certificate, error) {
+	return dcTestCerts["no dc"], nil
+}
+
 // Checks that the client suppports a version >= 1.3 and accepts Delegated
 // Credentials. If so, it returns the delegation certificate; otherwise it
 // returns a non-Delegated certificate.
@@ -507,8 +513,8 @@ func testConnWithDC(t *testing.T, clientMsg, serverMsg string, clientConfig, ser
 		}
 		serverCh <- server
 	}()
-
 	client, err := Dial("tcp", ln.Addr().String(), clientConfig)
+
 	if err != nil {
 		return false, err
 	}
@@ -552,20 +558,22 @@ func testConnWithDC(t *testing.T, clientMsg, serverMsg string, clientConfig, ser
 func TestDCHandshakeServerAuth(t *testing.T) {
 	serverMsg := "hello, client"
 	clientMsg := "hello, server"
-
+	initDCTest()
 	clientConfig := dcTestConfig.Clone()
 	serverConfig := dcTestConfig.Clone()
-	clientConfig.InsecureSkipVerify = true
 
 	for i, test := range dcServerTests {
 		clientConfig.SupportDelegatedCredential = test.clientDCSupport
-
-		initDCTest()
 		for dcCount = 0; dcCount < len(dcTestDCSignatureScheme); dcCount++ {
-			serverConfig.GetCertificate = testServerGetCertificate
+			if test.serverMaxVers < VersionTLS13 {
+				t.Logf("Server doesn't support DCs, not offering. test %d", i)
+				serverConfig.GetCertificate = testServerGetCertificateNoDC
+			} else {
+				serverConfig.GetCertificate = testServerGetCertificate
+			}
+
 			clientConfig.MaxVersion = test.clientMaxVers
 			serverConfig.MaxVersion = test.serverMaxVers
-
 			usedDC, err := testConnWithDC(t, clientMsg, serverMsg, clientConfig, serverConfig, "client")
 
 			if err != nil && test.expectSuccess {
@@ -586,6 +594,7 @@ func TestDCHandshakeClientAuth(t *testing.T) {
 	clientMsg := "hello, server"
 	serverMsg := "hello, client"
 
+	initDCTest()
 	serverConfig := dcTestConfig.Clone()
 	serverConfig.ClientAuth = RequestClientCert
 	serverConfig.GetCertificate = testServerGetCertificate
@@ -595,7 +604,6 @@ func TestDCHandshakeClientAuth(t *testing.T) {
 	for j, test := range dcClientTests {
 		serverConfig.SupportDelegatedCredential = test.serverDCSupport
 
-		initDCTest()
 		for dcCount = 0; dcCount < len(dcTestDCSignatureScheme); dcCount++ {
 			serverConfig.MaxVersion = test.serverMaxVers
 			clientConfig.MaxVersion = test.clientMaxVers
@@ -620,6 +628,7 @@ func TestDCHandshakeClientAndServerAuth(t *testing.T) {
 	clientMsg := "hello, server"
 	serverMsg := "hello, client"
 
+	initDCTest()
 	serverConfig := dcTestConfig.Clone()
 	serverConfig.ClientAuth = RequestClientCert
 	serverConfig.GetCertificate = testServerGetCertificate
@@ -632,8 +641,6 @@ func TestDCHandshakeClientAndServerAuth(t *testing.T) {
 	serverConfig.MaxVersion = VersionTLS13
 	clientConfig.MaxVersion = VersionTLS13
 
-	initDCTest()
-
 	usedDC, err := testConnWithDC(t, clientMsg, serverMsg, clientConfig, serverConfig, "both")
 
 	if err != nil {