Add indentityHash for algos that don't need hashing (#1340)

This adds hash.go and creates a identityHash that is used for algorithms
that do their own hashing (ED25519) for instance.

This unifies the hash variable naming between dnssec and sig(0) signing
and removes the special casing that existed for ED25519.

This unifies the variable naming between sig(0) and dnssec signing and
verifying.

I didn't want to used crypto.RegisterHash as not to fiddle with the
global namespaces of hashes, so the value of '0' from AlgorithmsToHash
is handled specially in dnssec and sig(0) code.

Note that ED448 isn't implemented at all.

Signed-off-by: Miek Gieben <miek@miek.nl>

dnssec.go

@@ -65,6 +65,9 @@ var AlgorithmToString = map[uint8]string{
 }
 
 // AlgorithmToHash is a map of algorithm crypto hash IDs to crypto.Hash's.
+// For newer algorithm that do their own hashing (i.e. ED25519) the returned value
+// is 0, implying no (external) hashing should occur. The non-exported identityHash is then
+// used.
 var AlgorithmToHash = map[uint8]crypto.Hash{
 	RSAMD5:           crypto.MD5, // Deprecated in RFC 6725
 	DSA:              crypto.SHA1,
@@ -74,7 +77,7 @@ var AlgorithmToHash = map[uint8]crypto.Hash{
 	ECDSAP256SHA256:  crypto.SHA256,
 	ECDSAP384SHA384:  crypto.SHA384,
 	RSASHA512:        crypto.SHA512,
-	ED25519:          crypto.Hash(0),
+	ED25519:          0,
 }
 
 // DNSSEC hashing algorithm codes.
@@ -296,35 +299,20 @@ func (rr *RRSIG) Sign(k crypto.Signer, rrset []RR) error {
 		return err
 	}
 
-	hash, ok := AlgorithmToHash[rr.Algorithm]
-	if !ok {
-		return ErrAlg
+	h, cryptohash, err := hashFromAlgorithm(rr.Algorithm)
+	if err != nil {
+		return err
 	}
 
 	switch rr.Algorithm {
-	case ED25519:
-		// ed25519 signs the raw message and performs hashing internally.
-		// All other supported signature schemes operate over the pre-hashed
-		// message, and thus ed25519 must be handled separately here.
-		//
-		// The raw message is passed directly into sign and crypto.Hash(0) is
-		// used to signal to the crypto.Signer that the data has not been hashed.
-		signature, err := sign(k, append(signdata, wire...), crypto.Hash(0), rr.Algorithm)
-		if err != nil {
-			return err
-		}
-
-		rr.Signature = toBase64(signature)
-		return nil
 	case RSAMD5, DSA, DSANSEC3SHA1:
 		// See RFC 6944.
 		return ErrAlg
 	default:
-		h := hash.New()
 		h.Write(signdata)
 		h.Write(wire)
 
-		signature, err := sign(k, h.Sum(nil), hash, rr.Algorithm)
+		signature, err := sign(k, h.Sum(nil), cryptohash, rr.Algorithm)
 		if err != nil {
 			return err
 		}
@@ -341,7 +329,7 @@ func sign(k crypto.Signer, hashed []byte, hash crypto.Hash, alg uint8) ([]byte,
 	}
 
 	switch alg {
-	case RSASHA1, RSASHA1NSEC3SHA1, RSASHA256, RSASHA512:
+	case RSASHA1, RSASHA1NSEC3SHA1, RSASHA256, RSASHA512, ED25519:
 		return signature, nil
 	case ECDSAP256SHA256, ECDSAP384SHA384:
 		ecdsaSignature := &struct {
@@ -362,8 +350,6 @@ func sign(k crypto.Signer, hashed []byte, hash crypto.Hash, alg uint8) ([]byte,
 		signature := intToBytes(ecdsaSignature.R, intlen)
 		signature = append(signature, intToBytes(ecdsaSignature.S, intlen)...)
 		return signature, nil
-	case ED25519:
-		return signature, nil
 	default:
 		return nil, ErrAlg
 	}
@@ -437,9 +423,9 @@ func (rr *RRSIG) Verify(k *DNSKEY, rrset []RR) error {
 		// remove the domain name and assume its ours?
 	}
 
-	hash, ok := AlgorithmToHash[rr.Algorithm]
-	if !ok {
-		return ErrAlg
+	h, cryptohash, err := hashFromAlgorithm(rr.Algorithm)
+	if err != nil {
+		return err
 	}
 
 	switch rr.Algorithm {
@@ -450,10 +436,9 @@ func (rr *RRSIG) Verify(k *DNSKEY, rrset []RR) error {
 			return ErrKey
 		}
 
-		h := hash.New()
 		h.Write(signeddata)
 		h.Write(wire)
-		return rsa.VerifyPKCS1v15(pubkey, hash, h.Sum(nil), sigbuf)
+		return rsa.VerifyPKCS1v15(pubkey, cryptohash, h.Sum(nil), sigbuf)
 
 	case ECDSAP256SHA256, ECDSAP384SHA384:
 		pubkey := k.publicKeyECDSA()
@@ -465,7 +450,6 @@ func (rr *RRSIG) Verify(k *DNSKEY, rrset []RR) error {
 		r := new(big.Int).SetBytes(sigbuf[:len(sigbuf)/2])
 		s := new(big.Int).SetBytes(sigbuf[len(sigbuf)/2:])
 
-		h := hash.New()
 		h.Write(signeddata)
 		h.Write(wire)
 		if ecdsa.Verify(pubkey, h.Sum(nil), r, s) {

hash.go

@@ -0,0 +1,31 @@
+package dns
+
+import (
+	"bytes"
+	"crypto"
+	"hash"
+)
+
+// identityHash will not hash, it only buffers the data written into it and returns it as-is.
+type identityHash struct {
+	b *bytes.Buffer
+}
+
+// Implement the hash.Hash interface.
+
+func (i identityHash) Write(b []byte) (int, error) { return i.b.Write(b) }
+func (i identityHash) Size() int                   { return i.b.Len() }
+func (i identityHash) BlockSize() int              { return 1024 }
+func (i identityHash) Reset()                      { i.b.Reset() }
+func (i identityHash) Sum(b []byte) []byte         { return append(b, i.b.Bytes()...) }
+
+func hashFromAlgorithm(alg uint8) (hash.Hash, crypto.Hash, error) {
+	hashnumber, ok := AlgorithmToHash[alg]
+	if !ok {
+		return nil, 0, ErrAlg
+	}
+	if hashnumber == 0 {
+		return identityHash{b: &bytes.Buffer{}}, hashnumber, nil
+	}
+	return hashnumber.New(), hashnumber, nil
+}

sig0.go

@@ -3,6 +3,7 @@ package dns
 import (
 	"crypto"
 	"crypto/ecdsa"
+	"crypto/ed25519"
 	"crypto/rsa"
 	"encoding/binary"
 	"math/big"
@@ -38,18 +39,17 @@ func (rr *SIG) Sign(k crypto.Signer, m *Msg) ([]byte, error) {
 	}
 	buf = buf[:off:cap(buf)]
 
-	hash, ok := AlgorithmToHash[rr.Algorithm]
-	if !ok {
-		return nil, ErrAlg
+	h, cryptohash, err := hashFromAlgorithm(rr.Algorithm)
+	if err != nil {
+		return nil, err
 	}
 
-	hasher := hash.New()
 	// Write SIG rdata
-	hasher.Write(buf[len(mbuf)+1+2+2+4+2:])
+	h.Write(buf[len(mbuf)+1+2+2+4+2:])
 	// Write message
-	hasher.Write(buf[:len(mbuf)])
+	h.Write(buf[:len(mbuf)])
 
-	signature, err := sign(k, hasher.Sum(nil), hash, rr.Algorithm)
+	signature, err := sign(k, h.Sum(nil), cryptohash, rr.Algorithm)
 	if err != nil {
 		return nil, err
 	}
@@ -82,20 +82,10 @@ func (rr *SIG) Verify(k *KEY, buf []byte) error {
 		return ErrKey
 	}
 
-	var hash crypto.Hash
-	switch rr.Algorithm {
-	case RSASHA1:
-		hash = crypto.SHA1
-	case RSASHA256, ECDSAP256SHA256:
-		hash = crypto.SHA256
-	case ECDSAP384SHA384:
-		hash = crypto.SHA384
-	case RSASHA512:
-		hash = crypto.SHA512
-	default:
-		return ErrAlg
-	}
-	hasher := hash.New()
+	h, cryptohash, err := hashFromAlgorithm(rr.Algorithm)
+	if err != nil {
+		return err
+	}
 
 	buflen := len(buf)
 	qdc := binary.BigEndian.Uint16(buf[4:])
@@ -103,7 +93,6 @@ func (rr *SIG) Verify(k *KEY, buf []byte) error {
 	auc := binary.BigEndian.Uint16(buf[8:])
 	adc := binary.BigEndian.Uint16(buf[10:])
 	offset := headerSize
-	var err error
 	for i := uint16(0); i < qdc && offset < buflen; i++ {
 		_, offset, err = UnpackDomainName(buf, offset)
 		if err != nil {
@@ -166,21 +155,21 @@ func (rr *SIG) Verify(k *KEY, buf []byte) error {
 		return &Error{err: "signer name doesn't match key name"}
 	}
 	sigend := offset
-	hasher.Write(buf[sigstart:sigend])
-	hasher.Write(buf[:10])
-	hasher.Write([]byte{
+	h.Write(buf[sigstart:sigend])
+	h.Write(buf[:10])
+	h.Write([]byte{
 		byte((adc - 1) << 8),
 		byte(adc - 1),
 	})
-	hasher.Write(buf[12:bodyend])
+	h.Write(buf[12:bodyend])
 
-	hashed := hasher.Sum(nil)
+	hashed := h.Sum(nil)
 	sig := buf[sigend:]
 	switch k.Algorithm {
 	case RSASHA1, RSASHA256, RSASHA512:
 		pk := k.publicKeyRSA()
 		if pk != nil {
-			return rsa.VerifyPKCS1v15(pk, hash, hashed, sig)
+			return rsa.VerifyPKCS1v15(pk, cryptohash, hashed, sig)
 		}
 	case ECDSAP256SHA256, ECDSAP384SHA384:
 		pk := k.publicKeyECDSA()
@@ -192,6 +181,14 @@ func (rr *SIG) Verify(k *KEY, buf []byte) error {
 			}
 			return ErrSig
 		}
+	case ED25519:
+		pk := k.publicKeyED25519()
+		if pk != nil {
+			if ed25519.Verify(pk, hashed, sig) {
+				return nil
+			}
+			return ErrSig
+		}
 	}
 	return ErrKeyAlg
 }

sig0_test.go

@@ -12,7 +12,7 @@ func TestSIG0(t *testing.T) {
 	}
 	m := new(Msg)
 	m.SetQuestion("example.org.", TypeSOA)
-	for _, alg := range []uint8{ECDSAP256SHA256, ECDSAP384SHA384, RSASHA1, RSASHA256, RSASHA512} {
+	for _, alg := range []uint8{ECDSAP256SHA256, ECDSAP384SHA384, RSASHA1, RSASHA256, RSASHA512, ED25519} {
 		algstr := AlgorithmToString[alg]
 		keyrr := new(KEY)
 		keyrr.Hdr.Name = algstr + "."
@@ -21,7 +21,7 @@ func TestSIG0(t *testing.T) {
 		keyrr.Algorithm = alg
 		keysize := 512
 		switch alg {
-		case ECDSAP256SHA256:
+		case ECDSAP256SHA256, ED25519:
 			keysize = 256
 		case ECDSAP384SHA384:
 			keysize = 384
@@ -30,7 +30,7 @@ func TestSIG0(t *testing.T) {
 		}
 		pk, err := keyrr.Generate(keysize)
 		if err != nil {
-			t.Errorf("failed to generate key for “%s”: %v", algstr, err)
+			t.Errorf("failed to generate key for %q: %v", algstr, err)
 			continue
 		}
 		now := uint32(time.Now().Unix())
@@ -45,16 +45,16 @@ func TestSIG0(t *testing.T) {
 		sigrr.SignerName = keyrr.Hdr.Name
 		mb, err := sigrr.Sign(pk.(crypto.Signer), m)
 		if err != nil {
-			t.Errorf("failed to sign message using “%s”: %v", algstr, err)
+			t.Errorf("failed to sign message using %q: %v", algstr, err)
 			continue
 		}
 		m := new(Msg)
 		if err := m.Unpack(mb); err != nil {
-			t.Errorf("failed to unpack message signed using “%s”: %v", algstr, err)
+			t.Errorf("failed to unpack message signed using %q: %v", algstr, err)
 			continue
 		}
 		if len(m.Extra) != 1 {
-			t.Errorf("missing SIG for message signed using “%s”", algstr)
+			t.Errorf("missing SIG for message signed using %q", algstr)
 			continue
 		}
 		var sigrrwire *SIG
@@ -71,20 +71,20 @@ func TestSIG0(t *testing.T) {
 				id = "sigrrwire"
 			}
 			if err := rr.Verify(keyrr, mb); err != nil {
-				t.Errorf("failed to verify “%s” signed SIG(%s): %v", algstr, id, err)
+				t.Errorf("failed to verify %q signed SIG(%s): %v", algstr, id, err)
 				continue
 			}
 		}
 		mb[13]++
 		if err := sigrr.Verify(keyrr, mb); err == nil {
-			t.Errorf("verify succeeded on an altered message using “%s”", algstr)
+			t.Errorf("verify succeeded on an altered message using %q", algstr)
 			continue
 		}
 		sigrr.Expiration = 2
 		sigrr.Inception = 1
 		mb, _ = sigrr.Sign(pk.(crypto.Signer), m)
 		if err := sigrr.Verify(keyrr, mb); err == nil {
-			t.Errorf("verify succeeded on an expired message using “%s”", algstr)
+			t.Errorf("verify succeeded on an expired message using %q", algstr)
 			continue
 		}
 	}