crypto: add package.

The crypto package is added as a common place to store identifiers for
hash functions. At the moment, the rsa package has an enumeration of
hash functions and knowledge of their digest lengths. This is an
unfortunate coupling and other high level crypto packages tend to need
to duplicate this enumeration and knowledge (i.e. openpgp).

crypto pulls this code out into a common location.

It would also make sense to add similar support for ciphers to crypto,
but the problem there isn't as acute that isn't done in this change.

R=bradfitzgo, r, rsc
CC=golang-dev
https://golang.org/cl/4080046

16 files changed, 153 insertions, 60 deletions

diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index 619e8aa261..6ba6951afc 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -28,6 +28,7 @@ DIRS=\
 	container/list\
 	container/ring\
 	container/vector\
+	crypto\
 	crypto/aes\
 	crypto/block\
 	crypto/blowfish\
@@ -154,6 +155,7 @@ DIRS+=\
 endif
 
 NOTEST=\
+	crypto\
 	debug/proc\
 	exp/draw/x11\
 	go/ast\
diff --git a/src/pkg/crypto/Makefile b/src/pkg/crypto/Makefile
new file mode 100644
index 0000000000..738a520623
--- /dev/null
+++ b/src/pkg/crypto/Makefile
@@ -0,0 +1,11 @@
+# Copyright 2011 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.
+
+include ../../Make.inc
+
+TARG=crypto
+GOFILES=\
+	crypto.go\
+
+include ../../Make.pkg
diff --git a/src/pkg/crypto/crypto.go b/src/pkg/crypto/crypto.go
new file mode 100644
index 0000000000..be6b34adf2
--- /dev/null
+++ b/src/pkg/crypto/crypto.go
@@ -0,0 +1,73 @@
+// Copyright 2011 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.
+
+// The crypto package collects common cryptographic constants.
+package crypto
+
+import (
+	"hash"
+)
+
+// Hash identifies a cryptographic hash function that is implemented in another
+// package.
+type Hash uint
+
+const (
+	MD4       Hash = 1 + iota // in package crypto/md4
+	MD5                       // in package crypto/md5
+	SHA1                      // in package crypto/sha1
+	SHA224                    // in package crypto/sha256
+	SHA256                    // in package crypto/sha256
+	SHA384                    // in package crypto/sha512
+	SHA512                    // in package crypto/sha512
+	MD5SHA1                   // no implementation; MD5+SHA1 used for TLS RSA
+	RIPEMD160                 // in package crypto/ripemd160
+	maxHash
+)
+
+var digestSizes = []uint8{
+	MD4:       16,
+	MD5:       16,
+	SHA1:      20,
+	SHA224:    28,
+	SHA256:    32,
+	SHA384:    48,
+	SHA512:    64,
+	MD5SHA1:   36,
+	RIPEMD160: 20,
+}
+
+// Size returns the length, in bytes, of a digest resulting from the given hash
+// function. It doesn't require that the hash function in question be linked
+// into the program.
+func (h Hash) Size() int {
+	if h > 0 && h < maxHash {
+		return int(digestSizes[h])
+	}
+	panic("crypto: Size of unknown hash function")
+}
+
+var hashes = make([]func() hash.Hash, maxHash)
+
+// New returns a new hash.Hash calculating the given hash function. If the
+// hash function is not linked into the binary, New returns nil.
+func (h Hash) New() hash.Hash {
+	if h > 0 && h < maxHash {
+		f := hashes[h]
+		if f != nil {
+			return f()
+		}
+	}
+	return nil
+}
+
+// RegisterHash registers a function that returns a new instance of the given
+// hash function. This is intended to be called from the init function in
+// packages that implement hash functions.
+func RegisterHash(h Hash, f func() hash.Hash) {
+	if h >= maxHash {
+		panic("crypto: RegisterHash of unknown hash function")
+	}
+	hashes[h] = f
+}
diff --git a/src/pkg/crypto/md4/md4.go b/src/pkg/crypto/md4/md4.go
index e13c986e68..ee46544a92 100644
--- a/src/pkg/crypto/md4/md4.go
+++ b/src/pkg/crypto/md4/md4.go
@@ -6,10 +6,15 @@
 package md4
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.MD4, New)
+}
+
 // The size of an MD4 checksum in bytes.
 const Size = 16
 
diff --git a/src/pkg/crypto/md5/md5.go b/src/pkg/crypto/md5/md5.go
index 54fddb63b9..8f93fc4b35 100644
--- a/src/pkg/crypto/md5/md5.go
+++ b/src/pkg/crypto/md5/md5.go
@@ -6,10 +6,15 @@
 package md5
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.MD5, New)
+}
+
 // The size of an MD5 checksum in bytes.
 const Size = 16
 
diff --git a/src/pkg/crypto/ocsp/ocsp.go b/src/pkg/crypto/ocsp/ocsp.go
index f3fa3bc834..f42d808888 100644
--- a/src/pkg/crypto/ocsp/ocsp.go
+++ b/src/pkg/crypto/ocsp/ocsp.go
@@ -9,8 +9,9 @@ package ocsp
 
 import (
 	"asn1"
+	"crypto"
 	"crypto/rsa"
-	"crypto/sha1"
+	_ "crypto/sha1"
 	"crypto/x509"
 	"os"
 	"time"
@@ -168,8 +169,8 @@ func ParseResponse(bytes []byte) (*Response, os.Error) {
 		return nil, x509.UnsupportedAlgorithmError{}
 	}
 
-	h := sha1.New()
-	hashType := rsa.HashSHA1
+	hashType := crypto.SHA1
+	h := hashType.New()
 
 	pub := ret.Certificate.PublicKey.(*rsa.PublicKey)
 	h.Write(basicResp.TBSResponseData.Raw)
diff --git a/src/pkg/crypto/ripemd160/ripemd160.go b/src/pkg/crypto/ripemd160/ripemd160.go
index 5614f1360e..6e88521c3f 100644
--- a/src/pkg/crypto/ripemd160/ripemd160.go
+++ b/src/pkg/crypto/ripemd160/ripemd160.go
@@ -10,10 +10,15 @@ package ripemd160
 // http://homes.esat.kuleuven.be/~cosicart/pdf/AB-9601/AB-9601.pdf.
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.RIPEMD160, New)
+}
+
 // The size of the checksum in bytes.
 const Size = 20
 
diff --git a/src/pkg/crypto/rsa/pkcs1v15.go b/src/pkg/crypto/rsa/pkcs1v15.go
index e4fc7d14a6..2eaadee24c 100644
--- a/src/pkg/crypto/rsa/pkcs1v15.go
+++ b/src/pkg/crypto/rsa/pkcs1v15.go
@@ -6,6 +6,7 @@ package rsa
 
 import (
 	"big"
+	"crypto"
 	"crypto/subtle"
 	"io"
 	"os"
@@ -139,19 +140,6 @@ func nonZeroRandomBytes(s []byte, rand io.Reader) (err os.Error) {
 	return
 }
 
-// Due to the design of PKCS#1 v1.5, we need to know the exact hash function in
-// use. A generic hash.Hash will not do.
-type PKCS1v15Hash int
-
-const (
-	HashMD5 PKCS1v15Hash = iota
-	HashSHA1
-	HashSHA256
-	HashSHA384
-	HashSHA512
-	HashMD5SHA1 // combined MD5 and SHA1 hash used for RSA signing in TLS.
-)
-
 // These are ASN1 DER structures:
 //   DigestInfo ::= SEQUENCE {
 //     digestAlgorithm AlgorithmIdentifier,
@@ -160,25 +148,20 @@ const (
 // For performance, we don't use the generic ASN1 encoder. Rather, we
 // precompute a prefix of the digest value that makes a valid ASN1 DER string
 // with the correct contents.
-var hashPrefixes = [][]byte{
-	// HashMD5
-	{0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10},
-	// HashSHA1
-	{0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
-	// HashSHA256
-	{0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
-	// HashSHA384
-	{0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30},
-	// HashSHA512
-	{0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40},
-	// HashMD5SHA1
-	{}, // A special TLS case which doesn't use an ASN1 prefix.
+var hashPrefixes = map[crypto.Hash][]byte{
+	crypto.MD5:       []byte{0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10},
+	crypto.SHA1:      []byte{0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
+	crypto.SHA256:    []byte{0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
+	crypto.SHA384:    []byte{0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30},
+	crypto.SHA512:    {0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40},
+	crypto.MD5SHA1:   {}, // A special TLS case which doesn't use an ASN1 prefix.
+	crypto.RIPEMD160: {0x30, 0x20, 0x30, 0x08, 0x06, 0x06, 0x28, 0xcf, 0x06, 0x03, 0x00, 0x31, 0x04, 0x14},
 }
 
 // SignPKCS1v15 calculates the signature of hashed using RSASSA-PKCS1-V1_5-SIGN from RSA PKCS#1 v1.5.
 // Note that hashed must be the result of hashing the input message using the
 // given hash function.
-func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash PKCS1v15Hash, hashed []byte) (s []byte, err os.Error) {
+func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) (s []byte, err os.Error) {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
 		return
@@ -211,7 +194,7 @@ func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash PKCS1v15Hash, hashed []
 // hashed is the result of hashing the input message using the given hash
 // function and sig is the signature. A valid signature is indicated by
 // returning a nil error.
-func VerifyPKCS1v15(pub *PublicKey, hash PKCS1v15Hash, hashed []byte, sig []byte) (err os.Error) {
+func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) (err os.Error) {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
 		return
@@ -246,28 +229,14 @@ func VerifyPKCS1v15(pub *PublicKey, hash PKCS1v15Hash, hashed []byte, sig []byte
 	return nil
 }
 
-func pkcs1v15HashInfo(hash PKCS1v15Hash, inLen int) (hashLen int, prefix []byte, err os.Error) {
-	switch hash {
-	case HashMD5:
-		hashLen = 16
-	case HashSHA1:
-		hashLen = 20
-	case HashSHA256:
-		hashLen = 32
-	case HashSHA384:
-		hashLen = 48
-	case HashSHA512:
-		hashLen = 64
-	case HashMD5SHA1:
-		hashLen = 36
-	default:
-		return 0, nil, os.ErrorString("unknown hash function")
-	}
-
+func pkcs1v15HashInfo(hash crypto.Hash, inLen int) (hashLen int, prefix []byte, err os.Error) {
+	hashLen = hash.Size()
 	if inLen != hashLen {
 		return 0, nil, os.ErrorString("input must be hashed message")
 	}
-
-	prefix = hashPrefixes[int(hash)]
+	prefix, ok := hashPrefixes[hash]
+	if !ok {
+		return 0, nil, os.ErrorString("unsupported hash function")
+	}
 	return
 }
diff --git a/src/pkg/crypto/rsa/pkcs1v15_test.go b/src/pkg/crypto/rsa/pkcs1v15_test.go
index bf6306dc29..7b2ce08cb0 100644
--- a/src/pkg/crypto/rsa/pkcs1v15_test.go
+++ b/src/pkg/crypto/rsa/pkcs1v15_test.go
@@ -7,6 +7,7 @@ package rsa
 import (
 	"big"
 	"bytes"
+	"crypto"
 	"crypto/rand"
 	"crypto/sha1"
 	"encoding/base64"
@@ -165,7 +166,7 @@ func TestSignPKCS1v15(t *testing.T) {
 		h.Write([]byte(test.in))
 		digest := h.Sum()
 
-		s, err := SignPKCS1v15(nil, rsaPrivateKey, HashSHA1, digest)
+		s, err := SignPKCS1v15(nil, rsaPrivateKey, crypto.SHA1, digest)
 		if err != nil {
 			t.Errorf("#%d %s", i, err)
 		}
@@ -185,7 +186,7 @@ func TestVerifyPKCS1v15(t *testing.T) {
 
 		sig, _ := hex.DecodeString(test.out)
 
-		err := VerifyPKCS1v15(&rsaPrivateKey.PublicKey, HashSHA1, digest, sig)
+		err := VerifyPKCS1v15(&rsaPrivateKey.PublicKey, crypto.SHA1, digest, sig)
 		if err != nil {
 			t.Errorf("#%d %s", i, err)
 		}
diff --git a/src/pkg/crypto/sha1/sha1.go b/src/pkg/crypto/sha1/sha1.go
index 8716c35910..e6aa096e2a 100644
--- a/src/pkg/crypto/sha1/sha1.go
+++ b/src/pkg/crypto/sha1/sha1.go
@@ -6,10 +6,15 @@
 package sha1
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.SHA1, New)
+}
+
 // The size of a SHA1 checksum in bytes.
 const Size = 20
 
diff --git a/src/pkg/crypto/sha256/sha256.go b/src/pkg/crypto/sha256/sha256.go
index 57a8ffa0d7..69b356b4e5 100644
--- a/src/pkg/crypto/sha256/sha256.go
+++ b/src/pkg/crypto/sha256/sha256.go
@@ -6,10 +6,16 @@
 package sha256
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.SHA224, New224)
+	crypto.RegisterHash(crypto.SHA256, New)
+}
+
 // The size of a SHA256 checksum in bytes.
 const Size = 32
 
diff --git a/src/pkg/crypto/sha512/sha512.go b/src/pkg/crypto/sha512/sha512.go
index c3cda97d96..7e9f330e59 100644
--- a/src/pkg/crypto/sha512/sha512.go
+++ b/src/pkg/crypto/sha512/sha512.go
@@ -6,10 +6,16 @@
 package sha512
 
 import (
+	"crypto"
 	"hash"
 	"os"
 )
 
+func init() {
+	crypto.RegisterHash(crypto.SHA384, New384)
+	crypto.RegisterHash(crypto.SHA512, New)
+}
+
 // The size of a SHA512 checksum in bytes.
 const Size = 64
 
diff --git a/src/pkg/crypto/tls/handshake_client.go b/src/pkg/crypto/tls/handshake_client.go
index 1ca33f59dd..19d2bfa3ba 100644
--- a/src/pkg/crypto/tls/handshake_client.go
+++ b/src/pkg/crypto/tls/handshake_client.go
@@ -5,6 +5,7 @@
 package tls
 
 import (
+	"crypto"
 	"crypto/rsa"
 	"crypto/subtle"
 	"crypto/x509"
@@ -248,7 +249,7 @@ func (c *Conn) clientHandshake() os.Error {
 		var digest [36]byte
 		copy(digest[0:16], finishedHash.serverMD5.Sum())
 		copy(digest[16:36], finishedHash.serverSHA1.Sum())
-		signed, err := rsa.SignPKCS1v15(c.config.rand(), c.config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, digest[0:])
+		signed, err := rsa.SignPKCS1v15(c.config.rand(), c.config.Certificates[0].PrivateKey, crypto.MD5SHA1, digest[0:])
 		if err != nil {
 			return c.sendAlert(alertInternalError)
 		}
diff --git a/src/pkg/crypto/tls/handshake_server.go b/src/pkg/crypto/tls/handshake_server.go
index 955811ada3..af46ea5113 100644
--- a/src/pkg/crypto/tls/handshake_server.go
+++ b/src/pkg/crypto/tls/handshake_server.go
@@ -5,6 +5,7 @@
 package tls
 
 import (
+	"crypto"
 	"crypto/rsa"
 	"crypto/subtle"
 	"crypto/x509"
@@ -213,7 +214,7 @@ Curves:
 		digest := make([]byte, 36)
 		copy(digest[0:16], finishedHash.serverMD5.Sum())
 		copy(digest[16:36], finishedHash.serverSHA1.Sum())
-		err = rsa.VerifyPKCS1v15(pub, rsa.HashMD5SHA1, digest, certVerify.signature)
+		err = rsa.VerifyPKCS1v15(pub, crypto.MD5SHA1, digest, certVerify.signature)
 		if err != nil {
 			c.sendAlert(alertBadCertificate)
 			return os.ErrorString("could not validate signature of connection nonces: " + err.String())
diff --git a/src/pkg/crypto/tls/key_agreement.go b/src/pkg/crypto/tls/key_agreement.go
index 861c64f04b..8edbb11900 100644
--- a/src/pkg/crypto/tls/key_agreement.go
+++ b/src/pkg/crypto/tls/key_agreement.go
@@ -6,6 +6,7 @@ package tls
 
 import (
 	"big"
+	"crypto"
 	"crypto/elliptic"
 	"crypto/md5"
 	"crypto/rsa"
@@ -143,7 +144,7 @@ Curve:
 	copy(serverECDHParams[4:], ecdhePublic)
 
 	md5sha1 := md5SHA1Hash(clientHello.random, hello.random, serverECDHParams)
-	sig, err := rsa.SignPKCS1v15(config.rand(), config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, md5sha1)
+	sig, err := rsa.SignPKCS1v15(config.rand(), config.Certificates[0].PrivateKey, crypto.MD5SHA1, md5sha1)
 	if err != nil {
 		return nil, os.ErrorString("failed to sign ECDHE parameters: " + err.String())
 	}
@@ -216,7 +217,7 @@ func (ka *ecdheRSAKeyAgreement) processServerKeyExchange(config *Config, clientH
 	sig = sig[2:]
 
 	md5sha1 := md5SHA1Hash(clientHello.random, serverHello.random, serverECDHParams)
-	return rsa.VerifyPKCS1v15(cert.PublicKey.(*rsa.PublicKey), rsa.HashMD5SHA1, md5sha1, sig)
+	return rsa.VerifyPKCS1v15(cert.PublicKey.(*rsa.PublicKey), crypto.MD5SHA1, md5sha1, sig)
 
 Error:
 	return os.ErrorString("invalid ServerKeyExchange")
diff --git a/src/pkg/crypto/x509/x509.go b/src/pkg/crypto/x509/x509.go
index 6199e8db9f..599263432b 100644
--- a/src/pkg/crypto/x509/x509.go
+++ b/src/pkg/crypto/x509/x509.go
@@ -9,6 +9,7 @@ import (
 	"asn1"
 	"big"
 	"container/vector"
+	"crypto"
 	"crypto/rsa"
 	"crypto/sha1"
 	"hash"
@@ -374,12 +375,12 @@ func (c *Certificate) CheckSignatureFrom(parent *Certificate) (err os.Error) {
 	// TODO(agl): don't ignore the path length constraint.
 
 	var h hash.Hash
-	var hashType rsa.PKCS1v15Hash
+	var hashType crypto.Hash
 
 	switch c.SignatureAlgorithm {
 	case SHA1WithRSA:
 		h = sha1.New()
-		hashType = rsa.HashSHA1
+		hashType = crypto.SHA1
 	default:
 		return UnsupportedAlgorithmError{}
 	}
@@ -840,7 +841,7 @@ func CreateCertificate(rand io.Reader, template, parent *Certificate, pub *rsa.P
 	h.Write(tbsCertContents)
 	digest := h.Sum()
 
-	signature, err := rsa.SignPKCS1v15(rand, priv, rsa.HashSHA1, digest)
+	signature, err := rsa.SignPKCS1v15(rand, priv, crypto.SHA1, digest)
 	if err != nil {
 		return
 	}