diff --git a/openpgp/packet/symmetric_key_encrypted.go b/openpgp/packet/symmetric_key_encrypted.go
index a78344f..30d02b2 100644
--- a/openpgp/packet/symmetric_key_encrypted.go
+++ b/openpgp/packet/symmetric_key_encrypted.go
@@ -6,11 +6,12 @@ package packet
 
 import (
 	"bytes"
-	"code.google.com/p/go.crypto/openpgp/errors"
-	"code.google.com/p/go.crypto/openpgp/s2k"
 	"crypto/cipher"
 	"io"
 	"strconv"
+
+	"code.google.com/p/go.crypto/openpgp/errors"
+	"code.google.com/p/go.crypto/openpgp/s2k"
 )
 
 // This is the largest session key that we'll support. Since no 512-bit cipher
@@ -119,7 +120,7 @@ func SerializeSymmetricKeyEncrypted(w io.Writer, passphrase []byte, config *Conf
 	keyEncryptingKey := make([]byte, keySize)
 	// s2k.Serialize salts and stretches the passphrase, and writes the
 	// resulting key to keyEncryptingKey and the s2k descriptor to s2kBuf.
-	err = s2k.Serialize(s2kBuf, keyEncryptingKey, config.Random(), passphrase)
+	err = s2k.Serialize(s2kBuf, keyEncryptingKey, config.Random(), passphrase, &s2k.Config{Hash: config.Hash()})
 	if err != nil {
 		return
 	}
diff --git a/openpgp/s2k/s2k.go b/openpgp/s2k/s2k.go
index aab3041..cf06a25 100644
--- a/openpgp/s2k/s2k.go
+++ b/openpgp/s2k/s2k.go
@@ -7,13 +7,33 @@
 package s2k
 
 import (
-	"code.google.com/p/go.crypto/openpgp/errors"
 	"crypto"
 	"hash"
 	"io"
 	"strconv"
+
+	"code.google.com/p/go.crypto/openpgp/errors"
 )
 
+// Config collects configuration parameters for s2k key-stretching
+// transformatioms. A nil *Config is valid and results in all default
+// values. Currently, Config is used only by the Serialize function in
+// this package.
+type Config struct {
+	// Hash is the default hash function to be used. If
+	// nil, SHA1 is used.
+	Hash crypto.Hash
+}
+
+func (c *Config) hash() crypto.Hash {
+	if c == nil || uint(c.Hash) == 0 {
+		// SHA1 is the historical default in this package.
+		return crypto.SHA1
+	}
+
+	return c.Hash
+}
+
 // Simple writes to out the result of computing the Simple S2K function (RFC
 // 4880, section 3.7.1.1) using the given hash and input passphrase.
 func Simple(out []byte, h hash.Hash, in []byte) {
@@ -126,12 +146,14 @@ func Parse(r io.Reader) (f func(out, in []byte), err error) {
 	return nil, errors.UnsupportedError("S2K function")
 }
 
-// Serialize salts and stretches the given passphrase and writes the resulting
-// key into key. It also serializes an S2K descriptor to w.
-func Serialize(w io.Writer, key []byte, rand io.Reader, passphrase []byte) error {
+// Serialize salts and stretches the given passphrase and writes the
+// resulting key into key. It also serializes an S2K descriptor to
+// w. The key stretching can be configured with c, which may be
+// nil. In that case, sensible defaults will be used.
+func Serialize(w io.Writer, key []byte, rand io.Reader, passphrase []byte, c *Config) error {
 	var buf [11]byte
 	buf[0] = 3 /* iterated and salted */
-	buf[1], _ = HashToHashId(crypto.SHA1)
+	buf[1], _ = HashToHashId(c.hash())
 	salt := buf[2:10]
 	if _, err := io.ReadFull(rand, salt); err != nil {
 		return err
@@ -142,7 +164,7 @@ func Serialize(w io.Writer, key []byte, rand io.Reader, passphrase []byte) error
 		return err
 	}
 
-	Iterated(key, crypto.SHA1.New(), passphrase, salt, count)
+	Iterated(key, c.hash().New(), passphrase, salt, count)
 	return nil
 }
 
diff --git a/openpgp/s2k/s2k_test.go b/openpgp/s2k/s2k_test.go
index 4898828..ed2255d 100644
--- a/openpgp/s2k/s2k_test.go
+++ b/openpgp/s2k/s2k_test.go
@@ -6,10 +6,16 @@ package s2k
 
 import (
 	"bytes"
+	"crypto"
+	_ "crypto/md5"
 	"crypto/rand"
 	"crypto/sha1"
+	_ "crypto/sha256"
+	_ "crypto/sha512"
 	"encoding/hex"
 	"testing"
+
+	_ "code.google.com/p/go.crypto/ripemd160"
 )
 
 var saltedTests = []struct {
@@ -96,10 +102,20 @@ func TestParse(t *testing.T) {
 }
 
 func TestSerialize(t *testing.T) {
+	hashes := []crypto.Hash{crypto.MD5, crypto.SHA1, crypto.RIPEMD160,
+		crypto.SHA256, crypto.SHA384, crypto.SHA512, crypto.SHA224}
+	for _, h := range hashes {
+		testSerializeConfig(t, &Config{Hash: h})
+	}
+}
+
+func testSerializeConfig(t *testing.T, c *Config) {
+	t.Logf("Running testSerializeConfig() with config: %+v", c)
+
 	buf := bytes.NewBuffer(nil)
 	key := make([]byte, 16)
 	passphrase := []byte("testing")
-	err := Serialize(buf, key, rand.Reader, passphrase)
+	err := Serialize(buf, key, rand.Reader, passphrase, c)
 	if err != nil {
 		t.Errorf("failed to serialize: %s", err)
 		return