diff --git a/ssh/certs.go b/ssh/certs.go
index ddece44..53bc8fd 100644
--- a/ssh/certs.go
+++ b/ssh/certs.go
@@ -68,10 +68,6 @@ func (c *OpenSSHCertV01) PublicKeyAlgo() string {
 	return algo
 }
 
-func (c *OpenSSHCertV01) RawKey() interface{} {
-	return c.Key.RawKey()
-}
-
 func (c *OpenSSHCertV01) PrivateKeyAlgo() string {
 	return c.Key.PrivateKeyAlgo()
 }
diff --git a/ssh/client_auth_test.go b/ssh/client_auth_test.go
index 4460b41..a726595 100644
--- a/ssh/client_auth_test.go
+++ b/ssh/client_auth_test.go
@@ -6,12 +6,7 @@ package ssh
 
 import (
 	"bytes"
-	"crypto"
 	"crypto/dsa"
-	"crypto/rsa"
-	"crypto/x509"
-	"encoding/pem"
-	"errors"
 	"io"
 	"io/ioutil"
 	"math/big"
@@ -62,32 +57,23 @@ rrxx26itVhJmcvoUhOjwuzSlP2bE5VHAvkGB352YBg==
 
 // keychain implements the ClientKeyring interface
 type keychain struct {
-	keys []interface{}
+	keys []Signer
 }
 
 func (k *keychain) Key(i int) (PublicKey, error) {
 	if i < 0 || i >= len(k.keys) {
 		return nil, nil
 	}
-	switch key := k.keys[i].(type) {
-	case *rsa.PrivateKey:
-		return NewRSAPublicKey(&key.PublicKey), nil
-	case *dsa.PrivateKey:
-		return NewDSAPublicKey(&key.PublicKey), nil
-	}
-	panic("unknown key type")
+
+	return k.keys[i].PublicKey(), nil
 }
 
 func (k *keychain) Sign(i int, rand io.Reader, data []byte) (sig []byte, err error) {
-	hashFunc := crypto.SHA1
-	h := hashFunc.New()
-	h.Write(data)
-	digest := h.Sum(nil)
-	switch key := k.keys[i].(type) {
-	case *rsa.PrivateKey:
-		return rsa.SignPKCS1v15(rand, key, hashFunc, digest)
-	}
-	return nil, errors.New("ssh: unknown key type")
+	return k.keys[i].Sign(rand, data)
+}
+
+func (k *keychain) add(key Signer) {
+	k.keys = append(k.keys, key)
 }
 
 func (k *keychain) loadPEM(file string) error {
@@ -95,15 +81,11 @@ func (k *keychain) loadPEM(file string) error {
 	if err != nil {
 		return err
 	}
-	block, _ := pem.Decode(buf)
-	if block == nil {
-		return errors.New("ssh: no key found")
-	}
-	r, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	key, err := ParsePrivateKey(buf)
 	if err != nil {
 		return err
 	}
-	k.keys = append(k.keys, r)
+	k.add(key)
 	return nil
 }
 
@@ -126,8 +108,8 @@ func (cr *keyboardInteractive) Challenge(user string, instruction string, questi
 
 // reused internally by tests
 var (
-	rsakey         *rsa.PrivateKey
-	dsakey         *dsa.PrivateKey
+	rsaKey         Signer
+	dsaKey         Signer
 	clientKeychain = new(keychain)
 	clientPassword = password("tiger")
 	serverConfig   = &ServerConfig{
@@ -135,8 +117,7 @@ var (
 			return user == "testuser" && pass == string(clientPassword)
 		},
 		PublicKeyCallback: func(conn *ServerConn, user, algo string, pubkey []byte) bool {
-			rsaKey := &clientKeychain.keys[0].(*rsa.PrivateKey).PublicKey
-			key := NewRSAPublicKey(rsaKey)
+			key, _ := clientKeychain.Key(0)
 			expected := MarshalPublicKey(key)
 			algoname := key.PublicKeyAlgo()
 			return user == "testuser" && algo == algoname && bytes.Equal(pubkey, expected)
@@ -157,21 +138,26 @@ var (
 )
 
 func init() {
-	if err := serverConfig.SetRSAPrivateKey([]byte(testServerPrivateKey)); err != nil {
+	var err error
+	rsaKey, err = ParsePrivateKey([]byte(testServerPrivateKey))
+	if err != nil {
 		panic("unable to set private key: " + err.Error())
 	}
+	rawDSAKey := new(dsa.PrivateKey)
 
-	block, _ := pem.Decode([]byte(testClientPrivateKey))
-	rsakey, _ = x509.ParsePKCS1PrivateKey(block.Bytes)
-
-	clientKeychain.keys = append(clientKeychain.keys, rsakey)
-	dsakey = new(dsa.PrivateKey)
 	// taken from crypto/dsa/dsa_test.go
-	dsakey.P, _ = new(big.Int).SetString("A9B5B793FB4785793D246BAE77E8FF63CA52F442DA763C440259919FE1BC1D6065A9350637A04F75A2F039401D49F08E066C4D275A5A65DA5684BC563C14289D7AB8A67163BFBF79D85972619AD2CFF55AB0EE77A9002B0EF96293BDD0F42685EBB2C66C327079F6C98000FBCB79AACDE1BC6F9D5C7B1A97E3D9D54ED7951FEF", 16)
-	dsakey.Q, _ = new(big.Int).SetString("E1D3391245933D68A0714ED34BBCB7A1F422B9C1", 16)
-	dsakey.G, _ = new(big.Int).SetString("634364FC25248933D01D1993ECABD0657CC0CB2CEED7ED2E3E8AECDFCDC4A25C3B15E9E3B163ACA2984B5539181F3EFF1A5E8903D71D5B95DA4F27202B77D2C44B430BB53741A8D59A8F86887525C9F2A6A5980A195EAA7F2FF910064301DEF89D3AA213E1FAC7768D89365318E370AF54A112EFBA9246D9158386BA1B4EEFDA", 16)
-	dsakey.Y, _ = new(big.Int).SetString("32969E5780CFE1C849A1C276D7AEB4F38A23B591739AA2FE197349AEEBD31366AEE5EB7E6C6DDB7C57D02432B30DB5AA66D9884299FAA72568944E4EEDC92EA3FBC6F39F53412FBCC563208F7C15B737AC8910DBC2D9C9B8C001E72FDC40EB694AB1F06A5A2DBD18D9E36C66F31F566742F11EC0A52E9F7B89355C02FB5D32D2", 16)
-	dsakey.X, _ = new(big.Int).SetString("5078D4D29795CBE76D3AACFE48C9AF0BCDBEE91A", 16)
+	rawDSAKey.P, _ = new(big.Int).SetString("A9B5B793FB4785793D246BAE77E8FF63CA52F442DA763C440259919FE1BC1D6065A9350637A04F75A2F039401D49F08E066C4D275A5A65DA5684BC563C14289D7AB8A67163BFBF79D85972619AD2CFF55AB0EE77A9002B0EF96293BDD0F42685EBB2C66C327079F6C98000FBCB79AACDE1BC6F9D5C7B1A97E3D9D54ED7951FEF", 16)
+	rawDSAKey.Q, _ = new(big.Int).SetString("E1D3391245933D68A0714ED34BBCB7A1F422B9C1", 16)
+	rawDSAKey.G, _ = new(big.Int).SetString("634364FC25248933D01D1993ECABD0657CC0CB2CEED7ED2E3E8AECDFCDC4A25C3B15E9E3B163ACA2984B5539181F3EFF1A5E8903D71D5B95DA4F27202B77D2C44B430BB53741A8D59A8F86887525C9F2A6A5980A195EAA7F2FF910064301DEF89D3AA213E1FAC7768D89365318E370AF54A112EFBA9246D9158386BA1B4EEFDA", 16)
+	rawDSAKey.Y, _ = new(big.Int).SetString("32969E5780CFE1C849A1C276D7AEB4F38A23B591739AA2FE197349AEEBD31366AEE5EB7E6C6DDB7C57D02432B30DB5AA66D9884299FAA72568944E4EEDC92EA3FBC6F39F53412FBCC563208F7C15B737AC8910DBC2D9C9B8C001E72FDC40EB694AB1F06A5A2DBD18D9E36C66F31F566742F11EC0A52E9F7B89355C02FB5D32D2", 16)
+	rawDSAKey.X, _ = new(big.Int).SetString("5078D4D29795CBE76D3AACFE48C9AF0BCDBEE91A", 16)
+
+	dsaKey, err = NewSignerFromKey(rawDSAKey)
+	if err != nil {
+		panic("NewSignerFromKey: " + err.Error())
+	}
+	clientKeychain.add(rsaKey)
+	serverConfig.AddHostKey(rsaKey)
 }
 
 // newMockAuthServer creates a new Server bound to
@@ -287,7 +273,8 @@ func TestClientAuthWrongKeyboardInteractive(t *testing.T) {
 // the mock server will only authenticate ssh-rsa keys
 func TestClientAuthInvalidPublicKey(t *testing.T) {
 	kc := new(keychain)
-	kc.keys = append(kc.keys, dsakey)
+
+	kc.add(dsaKey)
 	config := &ClientConfig{
 		User: "testuser",
 		Auth: []ClientAuth{
@@ -305,7 +292,8 @@ func TestClientAuthInvalidPublicKey(t *testing.T) {
 // the client should authenticate with the second key
 func TestClientAuthRSAandDSA(t *testing.T) {
 	kc := new(keychain)
-	kc.keys = append(kc.keys, dsakey, rsakey)
+	kc.add(dsaKey)
+	kc.add(rsaKey)
 	config := &ClientConfig{
 		User: "testuser",
 		Auth: []ClientAuth{
@@ -321,7 +309,7 @@ func TestClientAuthRSAandDSA(t *testing.T) {
 
 func TestClientHMAC(t *testing.T) {
 	kc := new(keychain)
-	kc.keys = append(kc.keys, rsakey)
+	kc.add(rsaKey)
 	for _, mac := range DefaultMACOrder {
 		config := &ClientConfig{
 			User: "testuser",
@@ -343,7 +331,6 @@ func TestClientHMAC(t *testing.T) {
 // issue 4285.
 func TestClientUnsupportedCipher(t *testing.T) {
 	kc := new(keychain)
-	kc.keys = append(kc.keys, rsakey)
 	config := &ClientConfig{
 		User: "testuser",
 		Auth: []ClientAuth{
@@ -362,7 +349,6 @@ func TestClientUnsupportedCipher(t *testing.T) {
 
 func TestClientUnsupportedKex(t *testing.T) {
 	kc := new(keychain)
-	kc.keys = append(kc.keys, rsakey)
 	config := &ClientConfig{
 		User: "testuser",
 		Auth: []ClientAuth{
diff --git a/ssh/common.go b/ssh/common.go
index e536c1a..7e6e5dc 100644
--- a/ssh/common.go
+++ b/ssh/common.go
@@ -6,7 +6,6 @@ package ssh
 
 import (
 	"crypto"
-	"crypto/elliptic"
 	"errors"
 	"fmt"
 	"math/big"
@@ -223,19 +222,6 @@ func (c *CryptoConfig) macs() []string {
 	return c.MACs
 }
 
-// ecHash returns the hash to match the given elliptic curve, see RFC
-// 5656, section 6.2.1
-func ecHash(curve elliptic.Curve) crypto.Hash {
-	bitSize := curve.Params().BitSize
-	switch {
-	case bitSize <= 256:
-		return crypto.SHA256
-	case bitSize <= 384:
-		return crypto.SHA384
-	}
-	return crypto.SHA512
-}
-
 // serialize a signed slice according to RFC 4254 6.6. The name should
 // be a key type name, rather than a cert type name.
 func serializeSignature(name string, sig []byte) []byte {
diff --git a/ssh/example_test.go b/ssh/example_test.go
index 715afb3..a88a677 100644
--- a/ssh/example_test.go
+++ b/ssh/example_test.go
@@ -23,14 +23,18 @@ func ExampleListen() {
 		},
 	}
 
-	pemBytes, err := ioutil.ReadFile("id_rsa")
+	privateBytes, err := ioutil.ReadFile("id_rsa")
 	if err != nil {
 		panic("Failed to load private key")
 	}
-	if err = config.SetRSAPrivateKey(pemBytes); err != nil {
+
+	private, err := ParsePrivateKey(privateBytes)
+	if err != nil {
 		panic("Failed to parse private key")
 	}
 
+	config.AddHostKey(private)
+
 	// Once a ServerConfig has been configured, connections can be
 	// accepted.
 	listener, err := Listen("tcp", "0.0.0.0:2022", config)
diff --git a/ssh/keys.go b/ssh/keys.go
index c135d3a..9738694 100644
--- a/ssh/keys.go
+++ b/ssh/keys.go
@@ -11,7 +11,12 @@ import (
 	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rsa"
+	"crypto/x509"
 	"encoding/base64"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
 	"math/big"
 )
 
@@ -209,12 +214,17 @@ type PublicKey interface {
 	// Verify that sig is a signature on the given data using this
 	// key. This function will hash the data appropriately first.
 	Verify(data []byte, sigBlob []byte) bool
-
-	// RawKey returns the underlying object, eg. *rsa.PublicKey.
-	RawKey() interface{}
 }
 
-// TODO(hanwen): define PrivateKey too.
+// A Signer is can create signatures that verify against a public key.
+type Signer interface {
+	// PublicKey returns an associated PublicKey instance.
+	PublicKey() PublicKey
+
+	// Sign returns raw signature for the given data. This method
+	// will apply the hash specified for the keytype to the data.
+	Sign(rand io.Reader, data []byte) ([]byte, error)
+}
 
 type rsaPublicKey rsa.PublicKey
 
@@ -223,11 +233,7 @@ func (r *rsaPublicKey) PrivateKeyAlgo() string {
 }
 
 func (r *rsaPublicKey) PublicKeyAlgo() string {
-	return "ssh-rsa"
-}
-
-func (r *rsaPublicKey) RawKey() interface{} {
-	return (*rsa.PublicKey)(r)
+	return r.PrivateKeyAlgo()
 }
 
 // parseRSA parses an RSA key according to RFC 4253, section 6.6.
@@ -250,7 +256,7 @@ func parseRSA(in []byte) (out PublicKey, rest []byte, ok bool) {
 	}
 
 	ok = true
-	return NewRSAPublicKey(key), in, ok
+	return (*rsaPublicKey)(key), in, ok
 }
 
 func (r *rsaPublicKey) Marshal() []byte {
@@ -273,8 +279,19 @@ func (r *rsaPublicKey) Verify(data []byte, sig []byte) bool {
 	return rsa.VerifyPKCS1v15((*rsa.PublicKey)(r), crypto.SHA1, digest, sig) == nil
 }
 
-func NewRSAPublicKey(k *rsa.PublicKey) PublicKey {
-	return (*rsaPublicKey)(k)
+type rsaPrivateKey struct {
+	*rsa.PrivateKey
+}
+
+func (r *rsaPrivateKey) PublicKey() PublicKey {
+	return (*rsaPublicKey)(&r.PrivateKey.PublicKey)
+}
+
+func (r *rsaPrivateKey) Sign(rand io.Reader, data []byte) ([]byte, error) {
+	h := crypto.SHA1.New()
+	h.Write(data)
+	digest := h.Sum(nil)
+	return rsa.SignPKCS1v15(rand, r.PrivateKey, crypto.SHA1, digest)
 }
 
 type dsaPublicKey dsa.PublicKey
@@ -282,11 +299,9 @@ type dsaPublicKey dsa.PublicKey
 func (r *dsaPublicKey) PrivateKeyAlgo() string {
 	return "ssh-dss"
 }
+
 func (r *dsaPublicKey) PublicKeyAlgo() string {
-	return "ssh-dss"
-}
-func (r *dsaPublicKey) RawKey() interface{} {
-	return (*dsa.PublicKey)(r)
+	return r.PrivateKeyAlgo()
 }
 
 // parseDSA parses an DSA key according to RFC 4253, section 6.6.
@@ -310,7 +325,7 @@ func parseDSA(in []byte) (out PublicKey, rest []byte, ok bool) {
 	}
 
 	ok = true
-	return NewDSAPublicKey(key), in, ok
+	return (*dsaPublicKey)(key), in, ok
 }
 
 func (r *dsaPublicKey) Marshal() []byte {
@@ -347,21 +362,33 @@ func (k *dsaPublicKey) Verify(data []byte, sigBlob []byte) bool {
 	return dsa.Verify((*dsa.PublicKey)(k), digest, r, s)
 }
 
-func NewDSAPublicKey(k *dsa.PublicKey) PublicKey {
-	return (*dsaPublicKey)(k)
+type dsaPrivateKey struct {
+	*dsa.PrivateKey
+}
+
+func (k *dsaPrivateKey) PublicKey() PublicKey {
+	return (*dsaPublicKey)(&k.PrivateKey.PublicKey)
+}
+
+func (k *dsaPrivateKey) Sign(rand io.Reader, data []byte) ([]byte, error) {
+	h := crypto.SHA1.New()
+	h.Write(data)
+	digest := h.Sum(nil)
+	r, s, err := dsa.Sign(rand, k.PrivateKey, digest)
+	if err != nil {
+		return nil, err
+	}
+
+	sig := make([]byte, 40)
+	copy(sig[:20], r.Bytes())
+	copy(sig[20:], s.Bytes())
+	return sig, nil
 }
 
 type ecdsaPublicKey ecdsa.PublicKey
 
-func NewECDSAPublicKey(k *ecdsa.PublicKey) PublicKey {
-	return (*ecdsaPublicKey)(k)
-}
-func (r *ecdsaPublicKey) RawKey() interface{} {
-	return (*ecdsa.PublicKey)(r)
-}
-
 func (key *ecdsaPublicKey) PrivateKeyAlgo() string {
-	return "ecdh-sha2-" + key.nistID()
+	return "ecdsa-sha2-" + key.nistID()
 }
 
 func (key *ecdsaPublicKey) nistID() string {
@@ -376,29 +403,25 @@ func (key *ecdsaPublicKey) nistID() string {
 	panic("ssh: unsupported ecdsa key size")
 }
 
-// RFC 5656, section 6.2.1 (for ECDSA).
-func (key *ecdsaPublicKey) hash() crypto.Hash {
-	switch key.Params().BitSize {
-	case 256:
+func supportedEllipticCurve(curve elliptic.Curve) bool {
+	return (curve == elliptic.P256() || curve == elliptic.P384() || curve == elliptic.P521())
+}
+
+// ecHash returns the hash to match the given elliptic curve, see RFC
+// 5656, section 6.2.1
+func ecHash(curve elliptic.Curve) crypto.Hash {
+	bitSize := curve.Params().BitSize
+	switch {
+	case bitSize <= 256:
 		return crypto.SHA256
-	case 384:
+	case bitSize <= 384:
 		return crypto.SHA384
-	case 521:
-		return crypto.SHA512
 	}
-	panic("ssh: unsupported ecdsa key size")
+	return crypto.SHA512
 }
 
 func (key *ecdsaPublicKey) PublicKeyAlgo() string {
-	switch key.Params().BitSize {
-	case 256:
-		return KeyAlgoECDSA256
-	case 384:
-		return KeyAlgoECDSA384
-	case 521:
-		return KeyAlgoECDSA521
-	}
-	panic("ssh: unsupported ecdsa key size")
+	return key.PrivateKeyAlgo()
 }
 
 // parseECDSA parses an ECDSA key according to RFC 5656, section 3.1.
@@ -432,7 +455,7 @@ func parseECDSA(in []byte) (out PublicKey, rest []byte, ok bool) {
 		ok = false
 		return
 	}
-	return NewECDSAPublicKey(key), in, ok
+	return (*ecdsaPublicKey)(key), in, ok
 }
 
 func (key *ecdsaPublicKey) Marshal() []byte {
@@ -450,7 +473,7 @@ func (key *ecdsaPublicKey) Marshal() []byte {
 }
 
 func (key *ecdsaPublicKey) Verify(data []byte, sigBlob []byte) bool {
-	h := key.hash().New()
+	h := ecHash(key.Curve).New()
 	h.Write(data)
 	digest := h.Sum(nil)
 
@@ -468,3 +491,100 @@ func (key *ecdsaPublicKey) Verify(data []byte, sigBlob []byte) bool {
 	}
 	return ecdsa.Verify((*ecdsa.PublicKey)(key), digest, r, s)
 }
+
+type ecdsaPrivateKey struct {
+	*ecdsa.PrivateKey
+}
+
+func (k *ecdsaPrivateKey) PublicKey() PublicKey {
+	return (*ecdsaPublicKey)(&k.PrivateKey.PublicKey)
+}
+
+func (k *ecdsaPrivateKey) Sign(rand io.Reader, data []byte) ([]byte, error) {
+	h := ecHash(k.PrivateKey.PublicKey.Curve).New()
+	h.Write(data)
+	digest := h.Sum(nil)
+	r, s, err := ecdsa.Sign(rand, k.PrivateKey, digest)
+	if err != nil {
+		return nil, err
+	}
+
+	sig := make([]byte, intLength(r)+intLength(s))
+	rest := marshalInt(sig, r)
+	marshalInt(rest, s)
+	return sig, nil
+}
+
+// NewPrivateKey takes a pointer to rsa, dsa or ecdsa PrivateKey
+// returns a corresponding Signer instance. EC keys should use P256,
+// P384 or P521.
+func NewSignerFromKey(k interface{}) (Signer, error) {
+	var sshKey Signer
+	switch t := k.(type) {
+	case *rsa.PrivateKey:
+		sshKey = &rsaPrivateKey{t}
+	case *dsa.PrivateKey:
+		sshKey = &dsaPrivateKey{t}
+	case *ecdsa.PrivateKey:
+		if !supportedEllipticCurve(t.Curve) {
+			return nil, errors.New("ssh: only P256, P384 and P521 EC keys are supported.")
+		}
+
+		sshKey = &ecdsaPrivateKey{t}
+	default:
+		return nil, fmt.Errorf("ssh: unsupported key type %T", k)
+	}
+	return sshKey, nil
+}
+
+// NewPublicKey takes a pointer to rsa, dsa or ecdsa PublicKey
+// and returns a corresponding ssh PublicKey instance. EC keys should use P256, P384 or P521.
+func NewPublicKey(k interface{}) (PublicKey, error) {
+	var sshKey PublicKey
+	switch t := k.(type) {
+	case *rsa.PublicKey:
+		sshKey = (*rsaPublicKey)(t)
+	case *ecdsa.PublicKey:
+		if !supportedEllipticCurve(t.Curve) {
+			return nil, errors.New("ssh: only P256, P384 and P521 EC keys are supported.")
+		}
+		sshKey = (*ecdsaPublicKey)(t)
+	case *dsa.PublicKey:
+		sshKey = (*dsaPublicKey)(t)
+	default:
+		return nil, fmt.Errorf("ssh: unsupported key type %T", k)
+	}
+	return sshKey, nil
+}
+
+// ParsePublicKey parses a PEM encoded private key. Currently, only
+// PKCS#1, RSA and ECDSA private keys are supported.
+func ParsePrivateKey(pemBytes []byte) (Signer, error) {
+	block, _ := pem.Decode(pemBytes)
+	if block == nil {
+		return nil, errors.New("ssh: no key found")
+	}
+
+	var rawkey interface{}
+	switch block.Type {
+	case "RSA PRIVATE KEY":
+		rsa, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+		if err != nil {
+			return nil, err
+		}
+		rawkey = rsa
+	case "EC PRIVATE KEY":
+		ec, err := x509.ParseECPrivateKey(block.Bytes)
+		if err != nil {
+			return nil, err
+		}
+		rawkey = ec
+
+		// TODO(hanwen): find doc for format and implement PEM parsing
+		// for DSA keys.
+	default:
+		return nil, fmt.Errorf("ssh: unsupported key type %q", block.Type)
+	}
+
+	return NewSignerFromKey(rawkey)
+}
diff --git a/ssh/keys_test.go b/ssh/keys_test.go
index b77cacb..fb3f21e 100644
--- a/ssh/keys_test.go
+++ b/ssh/keys_test.go
@@ -1,60 +1,138 @@
 package ssh
 
 import (
-	"crypto"
 	"crypto/dsa"
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
 	"reflect"
+	"strings"
 	"testing"
 )
 
-func TestRSAMarshal(t *testing.T) {
-	k0 := &rsakey.PublicKey
-	k1 := NewRSAPublicKey(k0)
-	k2, rest, ok := ParsePublicKey(MarshalPublicKey(k1))
-	if !ok {
-		t.Errorf("could not parse back Blob output")
+var ecdsaKey Signer
+
+func rawKey(pub PublicKey) interface{} {
+	switch k := pub.(type) {
+	case *rsaPublicKey:
+		return (*rsa.PublicKey)(k)
+	case *dsaPublicKey:
+		return (*dsa.PublicKey)(k)
+	case *ecdsaPublicKey:
+		return (*ecdsa.PublicKey)(k)
 	}
-	if len(rest) > 0 {
-		t.Errorf("trailing junk in RSA Blob() output")
-	}
-	if !reflect.DeepEqual(k0, k2.RawKey().(*rsa.PublicKey)) {
-		t.Errorf("got %#v in roundtrip, want %#v", k2.RawKey(), k0)
+	panic("unknown key type")
+}
+
+func TestKeyMarshalParse(t *testing.T) {
+	keys := []Signer{rsaKey, dsaKey, ecdsaKey}
+	for _, priv := range keys {
+		pub := priv.PublicKey()
+		roundtrip, rest, ok := ParsePublicKey(MarshalPublicKey(pub))
+		if !ok {
+			t.Errorf("ParsePublicKey(%T) failed", pub)
+		}
+
+		if len(rest) > 0 {
+			t.Errorf("ParsePublicKey(%T): trailing junk", pub)
+		}
+
+		k1 := rawKey(pub)
+		k2 := rawKey(roundtrip)
+
+		if !reflect.DeepEqual(k1, k2) {
+			t.Errorf("got %#v in roundtrip, want %#v", k2, k1)
+		}
 	}
 }
 
-func TestRSAKeyVerify(t *testing.T) {
-	pub := NewRSAPublicKey(&rsakey.PublicKey)
-
-	data := []byte("sign me")
-	h := crypto.SHA1.New()
-	h.Write(data)
-	digest := h.Sum(nil)
-
-	sig, err := rsa.SignPKCS1v15(rand.Reader, rsakey, crypto.SHA1, digest)
+func TestUnsupportedCurves(t *testing.T) {
+	raw, err := ecdsa.GenerateKey(elliptic.P224(), rand.Reader)
 	if err != nil {
-		t.Fatalf("SignPKCS1v15: %v", err)
+		t.Fatalf("GenerateKey: %v", err)
 	}
 
-	if !pub.Verify(data, sig) {
-		t.Errorf("publicKey.Verify failed")
+	if _, err = NewSignerFromKey(raw); err == nil || !strings.Contains(err.Error(), "only P256") {
+		t.Fatalf("NewPrivateKey should not succeed with P224, got: %v", err)
+	}
+
+	if _, err = NewPublicKey(&raw.PublicKey); err == nil || !strings.Contains(err.Error(), "only P256") {
+		t.Fatalf("NewPublicKey should not succeed with P224, got: %v", err)
 	}
 }
 
-func TestDSAMarshal(t *testing.T) {
-	k0 := &dsakey.PublicKey
-	k1 := NewDSAPublicKey(k0)
-	k2, rest, ok := ParsePublicKey(MarshalPublicKey(k1))
+func TestNewPublicKey(t *testing.T) {
+	keys := []Signer{rsaKey, dsaKey, ecdsaKey}
+	for _, k := range keys {
+		raw := rawKey(k.PublicKey())
+		pub, err := NewPublicKey(raw)
+		if err != nil {
+			t.Errorf("NewPublicKey(%#v): %v", raw, err)
+		}
+		if !reflect.DeepEqual(k.PublicKey(), pub) {
+			t.Errorf("NewPublicKey(%#v) = %#v, want %#v", raw, pub, k.PublicKey())
+		}
+	}
+}
+
+func TestKeySignVerify(t *testing.T) {
+	keys := []Signer{rsaKey, dsaKey, ecdsaKey}
+	for _, priv := range keys {
+		pub := priv.PublicKey()
+
+		data := []byte("sign me")
+		sig, err := priv.Sign(rand.Reader, data)
+		if err != nil {
+			t.Fatalf("Sign(%T): %v", priv, err)
+		}
+
+		if !pub.Verify(data, sig) {
+			t.Errorf("publicKey.Verify(%T) failed", priv)
+		}
+	}
+}
+
+func TestParseRSAPrivateKey(t *testing.T) {
+	key, err := ParsePrivateKey([]byte(testServerPrivateKey))
+	if err != nil {
+		t.Fatalf("ParsePrivateKey: %v", err)
+	}
+
+	rsa, ok := key.(*rsaPrivateKey)
 	if !ok {
-		t.Errorf("could not parse back Blob output")
+		t.Fatalf("got %T, want *rsa.PrivateKey", rsa)
 	}
-	if len(rest) > 0 {
-		t.Errorf("trailing junk in DSA Blob() output")
-	}
-	if !reflect.DeepEqual(k0, k2.RawKey().(*dsa.PublicKey)) {
-		t.Errorf("got %#v in roundtrip, want %#v", k2.RawKey(), k0)
+
+	if err := rsa.Validate(); err != nil {
+		t.Errorf("Validate: %v", err)
 	}
 }
 
-// TODO(hanwen): test for ECDSA marshal.
+func TestParseECPrivateKey(t *testing.T) {
+	// Taken from the data in test/ .
+	pem := []byte(`-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEINGWx0zo6fhJ/0EAfrPzVFyFC9s18lBt3cRoEDhS3ARooAoGCCqGSM49
+AwEHoUQDQgAEi9Hdw6KvZcWxfg2IDhA7UkpDtzzt6ZqJXSsFdLd+Kx4S3Sx4cVO+
+6/ZOXRnPmNAlLUqjShUsUBBngG0u2fqEqA==
+-----END EC PRIVATE KEY-----`)
+
+	key, err := ParsePrivateKey(pem)
+	if err != nil {
+		t.Fatalf("ParsePrivateKey: %v", err)
+	}
+
+	ecKey, ok := key.(*ecdsaPrivateKey)
+	if !ok {
+		t.Fatalf("got %T, want *ecdsaPrivateKey", ecKey)
+	}
+
+	if !validateECPublicKey(ecKey.Curve, ecKey.X, ecKey.Y) {
+		t.Fatalf("public key does not validate.")
+	}
+}
+
+func init() {
+	raw, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	ecdsaKey, _ = NewSignerFromKey(raw)
+}
diff --git a/ssh/server.go b/ssh/server.go
index dc5cd9f..ffc35dd 100644
--- a/ssh/server.go
+++ b/ssh/server.go
@@ -10,10 +10,7 @@ import (
 	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rand"
-	"crypto/rsa"
-	"crypto/x509"
 	"encoding/binary"
-	"encoding/pem"
 	"errors"
 	"io"
 	"math/big"
@@ -24,11 +21,7 @@ import (
 )
 
 type ServerConfig struct {
-	rsa *rsa.PrivateKey
-
-	// rsaSerialized is the serialized form of the public key that
-	// corresponds to the private key held in the rsa field.
-	rsaSerialized []byte
+	hostKeys []Signer
 
 	// Rand provides the source of entropy for key exchange. If Rand is
 	// nil, the cryptographic random reader in package crypto/rand will
@@ -69,21 +62,29 @@ func (c *ServerConfig) rand() io.Reader {
 	return c.Rand
 }
 
+// AddHostKey adds a private key as a host key. If an existing host
+// key exists with the same algorithm, it is overwritten.
+func (s *ServerConfig) AddHostKey(key Signer) {
+	for i, k := range s.hostKeys {
+		if k.PublicKey().PublicKeyAlgo() == key.PublicKey().PublicKeyAlgo() {
+			s.hostKeys[i] = key
+			return
+		}
+	}
+
+	s.hostKeys = append(s.hostKeys, key)
+}
+
 // SetRSAPrivateKey sets the private key for a Server. A Server must have a
 // private key configured in order to accept connections. The private key must
 // be in the form of a PEM encoded, PKCS#1, RSA private key. The file "id_rsa"
 // typically contains such a key.
 func (s *ServerConfig) SetRSAPrivateKey(pemBytes []byte) error {
-	block, _ := pem.Decode(pemBytes)
-	if block == nil {
-		return errors.New("ssh: no key found")
-	}
-	rsa, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	priv, err := ParsePrivateKey(pemBytes)
 	if err != nil {
 		return err
 	}
-	s.rsa = rsa
-	s.rsaSerialized = MarshalPublicKey(NewRSAPublicKey(&rsa.PublicKey))
+	s.AddHostKey(priv)
 	return nil
 }
 
@@ -141,7 +142,7 @@ func Server(c net.Conn, config *ServerConfig) *ServerConn {
 
 // kexECDH performs Elliptic Curve Diffie-Hellman key agreement on a
 // ServerConnection, as documented in RFC 5656, section 4.
-func (s *ServerConn) kexECDH(curve elliptic.Curve, magics *handshakeMagics, hostKeyAlgo string) (result *kexResult, err error) {
+func (s *ServerConn) kexECDH(curve elliptic.Curve, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
 	packet, err := s.readPacket()
 	if err != nil {
 		return
@@ -169,7 +170,7 @@ func (s *ServerConn) kexECDH(curve elliptic.Curve, magics *handshakeMagics, host
 		return nil, err
 	}
 
-	hostKeyBytes := s.config.rsaSerialized
+	hostKeyBytes := MarshalPublicKey(priv.PublicKey())
 
 	serializedEphKey := elliptic.Marshal(curve, ephKey.PublicKey.X, ephKey.PublicKey.Y)
 
@@ -192,7 +193,9 @@ func (s *ServerConn) kexECDH(curve elliptic.Curve, magics *handshakeMagics, host
 
 	H := h.Sum(nil)
 
-	sig, err := s.serializedHostKeySignature(hostKeyAlgo, H)
+	// H is already a hash, but the hostkey signing will apply its
+	// own key specific hash algorithm.
+	sig, err := signAndMarshal(priv, s.config.rand(), H)
 	if err != nil {
 		return nil, err
 	}
@@ -247,7 +250,7 @@ func validateECPublicKey(curve elliptic.Curve, x, y *big.Int) bool {
 }
 
 // kexDH performs Diffie-Hellman key agreement on a ServerConnection.
-func (s *ServerConn) kexDH(group *dhGroup, hashFunc crypto.Hash, magics *handshakeMagics, hostKeyAlgo string) (result *kexResult, err error) {
+func (s *ServerConn) kexDH(group *dhGroup, hashFunc crypto.Hash, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
 	packet, err := s.readPacket()
 	if err != nil {
 		return
@@ -268,7 +271,7 @@ func (s *ServerConn) kexDH(group *dhGroup, hashFunc crypto.Hash, magics *handsha
 		return nil, err
 	}
 
-	hostKeyBytes := s.config.rsaSerialized
+	hostKeyBytes := MarshalPublicKey(priv.PublicKey())
 
 	h := hashFunc.New()
 	writeString(h, magics.clientVersion)
@@ -285,7 +288,9 @@ func (s *ServerConn) kexDH(group *dhGroup, hashFunc crypto.Hash, magics *handsha
 
 	H := h.Sum(nil)
 
-	sig, err := s.serializedHostKeySignature(hostKeyAlgo, H)
+	// H is already a hash, but the hostkey signing will apply its
+	// own key specific hash algorithm.
+	sig, err := signAndMarshal(priv, s.config.rand(), H)
 	if err != nil {
 		return nil, err
 	}
@@ -306,25 +311,15 @@ func (s *ServerConn) kexDH(group *dhGroup, hashFunc crypto.Hash, magics *handsha
 	}, nil
 }
 
-// serializedHostKeySignature signs the hashed data, and serializes
-// the signature according to SSH conventions.
-func (s *ServerConn) serializedHostKeySignature(hostKeyAlgo string, hashed []byte) ([]byte, error) {
-	var sig []byte
-	switch hostKeyAlgo {
-	case hostAlgoRSA:
-		hashFunc := crypto.SHA1
-		hh := hashFunc.New()
-		hh.Write(hashed)
-		var err error
-		sig, err = rsa.SignPKCS1v15(s.config.rand(), s.config.rsa, hashFunc, hh.Sum(nil))
-		if err != nil {
-			return nil, err
-		}
-	default:
-		return nil, errors.New("ssh: internal error")
+// signAndMarshal signs the data with the appropriate algorithm,
+// and serializes the result in SSH wire format.
+func signAndMarshal(k Signer, rand io.Reader, data []byte) ([]byte, error) {
+	sig, err := k.Sign(rand, data)
+	if err != nil {
+		return nil, err
 	}
 
-	return serializeSignature(hostKeyAlgo, sig), nil
+	return serializeSignature(k.PublicKey().PrivateKeyAlgo(), sig), nil
 }
 
 // serverVersion is the fixed identification string that Server will use.
@@ -374,7 +369,6 @@ func (s *ServerConn) Handshake() (err error) {
 func (s *ServerConn) clientInitHandshake(clientKexInit *kexInitMsg, clientKexInitPacket []byte) (err error) {
 	serverKexInit := kexInitMsg{
 		KexAlgos:                s.config.Crypto.kexes(),
-		ServerHostKeyAlgos:      supportedHostKeyAlgos,
 		CiphersClientServer:     s.config.Crypto.ciphers(),
 		CiphersServerClient:     s.config.Crypto.ciphers(),
 		MACsClientServer:        s.config.Crypto.macs(),
@@ -382,8 +376,12 @@ func (s *ServerConn) clientInitHandshake(clientKexInit *kexInitMsg, clientKexIni
 		CompressionClientServer: supportedCompressions,
 		CompressionServerClient: supportedCompressions,
 	}
-	serverKexInitPacket := marshal(msgKexInit, serverKexInit)
+	for _, k := range s.config.hostKeys {
+		serverKexInit.ServerHostKeyAlgos = append(
+			serverKexInit.ServerHostKeyAlgos, k.PublicKey().PublicKeyAlgo())
+	}
 
+	serverKexInitPacket := marshal(msgKexInit, serverKexInit)
 	if err = s.writePacket(serverKexInitPacket); err != nil {
 		return
 	}
@@ -410,6 +408,13 @@ func (s *ServerConn) clientInitHandshake(clientKexInit *kexInitMsg, clientKexIni
 		}
 	}
 
+	var hostKey Signer
+	for _, k := range s.config.hostKeys {
+		if hostKeyAlgo == k.PublicKey().PublicKeyAlgo() {
+			hostKey = k
+		}
+	}
+
 	var magics handshakeMagics
 	magics.serverVersion = serverVersion[:len(serverVersion)-2]
 	magics.clientVersion = s.ClientVersion
@@ -419,17 +424,17 @@ func (s *ServerConn) clientInitHandshake(clientKexInit *kexInitMsg, clientKexIni
 	var result *kexResult
 	switch kexAlgo {
 	case kexAlgoECDH256:
-		result, err = s.kexECDH(elliptic.P256(), &magics, hostKeyAlgo)
+		result, err = s.kexECDH(elliptic.P256(), &magics, hostKey)
 	case kexAlgoECDH384:
-		result, err = s.kexECDH(elliptic.P384(), &magics, hostKeyAlgo)
+		result, err = s.kexECDH(elliptic.P384(), &magics, hostKey)
 	case kexAlgoECDH521:
-		result, err = s.kexECDH(elliptic.P521(), &magics, hostKeyAlgo)
+		result, err = s.kexECDH(elliptic.P521(), &magics, hostKey)
 	case kexAlgoDH14SHA1:
 		dhGroup14Once.Do(initDHGroup14)
-		result, err = s.kexDH(dhGroup14, crypto.SHA1, &magics, hostKeyAlgo)
+		result, err = s.kexDH(dhGroup14, crypto.SHA1, &magics, hostKey)
 	case kexAlgoDH1SHA1:
 		dhGroup1Once.Do(initDHGroup1)
-		result, err = s.kexDH(dhGroup1, crypto.SHA1, &magics, hostKeyAlgo)
+		result, err = s.kexDH(dhGroup1, crypto.SHA1, &magics, hostKey)
 	default:
 		err = errors.New("ssh: unexpected key exchange algorithm " + kexAlgo)
 	}
diff --git a/ssh/test/keys_test.go b/ssh/test/keys_test.go
index 363872c..b116422 100644
--- a/ssh/test/keys_test.go
+++ b/ssh/test/keys_test.go
@@ -1,8 +1,6 @@
 package test
 
 import (
-	"crypto/x509"
-	"encoding/pem"
 	"reflect"
 	"strings"
 	"testing"
@@ -171,16 +169,12 @@ func testAuthorizedKeys(t *testing.T, authKeys []byte, expected []authResult) {
 }
 
 func getTestPublicKey(t *testing.T) ssh.PublicKey {
-	block, _ := pem.Decode([]byte(testClientPrivateKey))
-	if block == nil {
-		t.Fatalf("pem.Decode: %v", testClientPrivateKey)
-	}
-	priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	priv, err := ssh.ParsePrivateKey([]byte(testClientPrivateKey))
 	if err != nil {
-		t.Fatalf("x509.ParsePKCS1PrivateKey: %v", err)
+		t.Fatalf("ParsePrivateKey: %v", err)
 	}
 
-	return ssh.NewRSAPublicKey(&priv.PublicKey)
+	return priv.PublicKey()
 }
 
 func TestAuth(t *testing.T) {
diff --git a/ssh/test/test_unix_test.go b/ssh/test/test_unix_test.go
index 7ab5e22..6311876 100644
--- a/ssh/test/test_unix_test.go
+++ b/ssh/test/test_unix_test.go
@@ -10,12 +10,7 @@ package test
 
 import (
 	"bytes"
-	"crypto"
-	"crypto/dsa"
-	"crypto/rsa"
-	"crypto/x509"
-	"encoding/pem"
-	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
@@ -53,25 +48,23 @@ HostbasedAuthentication no
 `
 
 var (
-	configTmpl        template.Template
-	rsakey            *rsa.PrivateKey
-	serializedHostKey []byte
+	configTmpl template.Template
+	privateKey ssh.Signer
+	hostKey    ssh.Signer
 )
 
 func init() {
 	template.Must(configTmpl.Parse(sshd_config))
-	block, _ := pem.Decode([]byte(testClientPrivateKey))
-	rsakey, _ = x509.ParsePKCS1PrivateKey(block.Bytes)
 
-	block, _ = pem.Decode([]byte(keys["ssh_host_rsa_key"]))
-	if block == nil {
-		panic("pem.Decode ssh_host_rsa_key")
-	}
-	priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	var err error
+	hostKey, err = ssh.ParsePrivateKey([]byte(keys["ssh_host_rsa_key"]))
 	if err != nil {
-		panic("ParsePKCS1PrivateKey: " + err.Error())
+		panic("ParsePrivateKey: " + err.Error())
+	}
+	privateKey, err = ssh.ParsePrivateKey([]byte(testClientPrivateKey))
+	if err != nil {
+		panic("ParsePrivateKey: " + err.Error())
 	}
-	serializedHostKey = ssh.MarshalPublicKey(ssh.NewRSAPublicKey(&priv.PublicKey))
 }
 
 type server struct {
@@ -106,26 +99,26 @@ type storedHostKey struct {
 	keys map[string][]byte
 }
 
-func (k *storedHostKey) Add(algo string, public []byte) {
+func (k *storedHostKey) Add(key ssh.PublicKey) {
 	if k.keys == nil {
 		k.keys = map[string][]byte{}
 	}
-	k.keys[algo] = append([]byte(nil), public...)
+	k.keys[key.PublicKeyAlgo()] = append([]byte(nil), ssh.MarshalPublicKey(key)...)
 }
 
 func (k *storedHostKey) Check(addr string, remote net.Addr, algo string, key []byte) error {
 	if k.keys == nil || bytes.Compare(key, k.keys[algo]) != 0 {
-		return errors.New("host key mismatch")
+		return fmt.Errorf("host key mismatch. Got %q, want %q", key, k.keys[algo])
 	}
 	return nil
 }
 
 func clientConfig() *ssh.ClientConfig {
 	keyChecker := storedHostKey{}
-	keyChecker.Add("ssh-rsa", serializedHostKey)
+	keyChecker.Add(hostKey.PublicKey())
 
 	kc := new(keychain)
-	kc.keys = append(kc.keys, rsakey)
+	kc.keys = append(kc.keys, privateKey)
 	config := &ssh.ClientConfig{
 		User: username(),
 		Auth: []ssh.ClientAuth{
@@ -261,34 +254,20 @@ func newServer(t *testing.T) *server {
 	}
 }
 
-// keychain implements the ClientKeyring interface
+// keychain implements the ClientKeyring interface.
 type keychain struct {
-	keys []interface{}
+	keys []ssh.Signer
 }
 
 func (k *keychain) Key(i int) (ssh.PublicKey, error) {
 	if i < 0 || i >= len(k.keys) {
 		return nil, nil
 	}
-	switch key := k.keys[i].(type) {
-	case *rsa.PrivateKey:
-		return ssh.NewRSAPublicKey(&key.PublicKey), nil
-	case *dsa.PrivateKey:
-		return ssh.NewDSAPublicKey(&key.PublicKey), nil
-	}
-	panic("unknown key type")
+	return k.keys[i].PublicKey(), nil
 }
 
 func (k *keychain) Sign(i int, rand io.Reader, data []byte) (sig []byte, err error) {
-	hashFunc := crypto.SHA1
-	h := hashFunc.New()
-	h.Write(data)
-	digest := h.Sum(nil)
-	switch key := k.keys[i].(type) {
-	case *rsa.PrivateKey:
-		return rsa.SignPKCS1v15(rand, key, hashFunc, digest)
-	}
-	return nil, errors.New("ssh: unknown key type")
+	return k.keys[i].Sign(rand, data)
 }
 
 func (k *keychain) loadPEM(file string) error {
@@ -296,14 +275,10 @@ func (k *keychain) loadPEM(file string) error {
 	if err != nil {
 		return err
 	}
-	block, _ := pem.Decode(buf)
-	if block == nil {
-		return errors.New("ssh: no key found")
-	}
-	r, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	key, err := ssh.ParsePrivateKey(buf)
 	if err != nil {
 		return err
 	}
-	k.keys = append(k.keys, r)
+	k.keys = append(k.keys, key)
 	return nil
 }