diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index 619e8aa2612..6ba6951afc3 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 00000000000..738a5206232
--- /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 00000000000..be6b34adf28
--- /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 e13c986e686..ee46544a920 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 54fddb63b93..8f93fc4b354 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 f3fa3bc834c..f42d8088884 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 5614f1360eb..6e88521c3f6 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 e4fc7d14a6b..2eaadee24c2 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 bf6306dc29b..7b2ce08cb0b 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 8716c359107..e6aa096e2a6 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 57a8ffa0d76..69b356b4e51 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 c3cda97d968..7e9f330e594 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 1ca33f59dd0..19d2bfa3ba7 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 955811ada35..af46ea51133 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 861c64f04bb..8edbb11900c 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 6199e8db9f5..599263432b5 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
 	}