go.crypto/openpgp: fix hash presence checks.

At some point in the distant past, crypto.Hash.New() changed from
returning nil when a hash function wasn't provided, to panicing. Some
of the code in openpgp predates this and was still using the nil check.

LGTM=bradfitz
R=sburford, bradfitz
CC=golang-codereviews
https://golang.org/cl/104850045

openpgp/clearsign/clearsign.go

@@ -296,10 +296,10 @@ func Encode(w io.Writer, privateKey *packet.PrivateKey, config *packet.Config) (
 		return nil, errors.UnsupportedError("unknown hash type: " + strconv.Itoa(int(hashType)))
 	}
 
-	h := hashType.New()
-	if h == nil {
+	if !hashType.Available() {
 		return nil, errors.UnsupportedError("unsupported hash type: " + strconv.Itoa(int(hashType)))
 	}
+	h := hashType.New()
 
 	buffered := bufio.NewWriter(w)
 	// start has a \n at the beginning that we don't want here.

openpgp/packet/public_key_v3.go

@@ -237,9 +237,10 @@ func (pk *PublicKeyV3) VerifyKeySignatureV3(signed *PublicKeyV3, sig *SignatureV
 // userIdSignatureV3Hash returns a Hash of the message that needs to be signed
 // to assert that pk is a valid key for id.
 func userIdSignatureV3Hash(id string, pk signingKey, hfn crypto.Hash) (h hash.Hash, err error) {
-	if h = hfn.New(); h == nil {
+	if !hfn.Available() {
 		return nil, errors.UnsupportedError("hash function")
 	}
+	h = hfn.New()
 
 	// RFC 4880, section 5.2.4
 	pk.SerializeSignaturePrefix(h)

openpgp/read.go

@@ -276,10 +276,10 @@ FindLiteralData:
 // returns two hashes. The second should be used to hash the message itself and
 // performs any needed preprocessing.
 func hashForSignature(hashId crypto.Hash, sigType packet.SignatureType) (hash.Hash, hash.Hash, error) {
-	h := hashId.New()
-	if h == nil {
+	if !hashId.Available() {
 		return nil, nil, errors.UnsupportedError("hash not available: " + strconv.Itoa(int(hashId)))
 	}
+	h := hashId.New()
 
 	switch sigType {
 	case packet.SigTypeBinary:

openpgp/read_test.go

@@ -11,6 +11,7 @@ import (
 	"encoding/hex"
 	"io"
 	"io/ioutil"
+	"strings"
 	"testing"
 )
 
@@ -285,6 +286,33 @@ func TestDetachedSignatureDSA(t *testing.T) {
 	testDetachedSignature(t, kring, readerFromHex(detachedSignatureDSAHex), signedInput, "binary", testKey3KeyId)
 }
 
+func testHashFunctionError(t *testing.T, signatureHex string) {
+	kring, _ := ReadKeyRing(readerFromHex(testKeys1And2Hex))
+	_, err := CheckDetachedSignature(kring, nil, readerFromHex(signatureHex))
+	if err == nil {
+		t.Fatal("Packet with bad hash type was correctly parsed")
+	}
+	unsupported, ok := err.(errors.UnsupportedError)
+	if !ok {
+		t.Fatalf("Unexpected class of error: %s", err)
+	}
+	if !strings.Contains(string(unsupported), "hash ") {
+		t.Fatalf("Unexpected error: %s", err)
+	}
+}
+
+func TestUnknownHashFunction(t *testing.T) {
+	// unknownHashFunctionHex contains a signature packet with hash
+	// function type 153 (which isn't a real hash function id).
+	testHashFunctionError(t, unknownHashFunctionHex)
+}
+
+func TestMissingHashFunction(t *testing.T) {
+	// missingHashFunctionHex contains a signature packet that uses
+	// RIPEMD160, which isn't compiled in.
+	testHashFunctionError(t, missingHashFunctionHex)
+}
+
 func TestReadingArmoredPrivateKey(t *testing.T) {
 	el, err := ReadArmoredKeyRing(bytes.NewBufferString(armoredPrivateKeyBlock))
 	if err != nil {
@@ -373,3 +401,7 @@ VrM0m72/jnpKo04=
 -----END PGP PRIVATE KEY BLOCK-----`
 
 const dsaKeyWithSHA512 = `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`
+
+const unknownHashFunctionHex = `8a00000040040001990006050253863c24000a09103b4fe6acc0b21f32ffff01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101`
+
+const missingHashFunctionHex = `8a00000040040001030006050253863c24000a09103b4fe6acc0b21f32ffff01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101`

openpgp/s2k/s2k.go

@@ -91,10 +91,10 @@ func Parse(r io.Reader) (f func(out, in []byte), err error) {
 	if !ok {
 		return nil, errors.UnsupportedError("hash for S2K function: " + strconv.Itoa(int(buf[1])))
 	}
-	h := hash.New()
-	if h == nil {
+	if !hash.Available() {
 		return nil, errors.UnsupportedError("hash not available: " + strconv.Itoa(int(hash)))
 	}
+	h := hash.New()
 
 	switch buf[0] {
 	case 0: