diff --git a/nacl/sign/sign.go b/nacl/sign/sign.go
new file mode 100644
index 0000000..a9ac0a7
--- /dev/null
+++ b/nacl/sign/sign.go
@@ -0,0 +1,83 @@
+// Copyright 2018 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.
+
+// Package sign signs small messages using public-key cryptography.
+//
+// Sign uses Ed25519 to sign messages. The length of messages is not hidden.
+// Messages should be small because:
+// 1. The whole message needs to be held in memory to be processed.
+// 2. Using large messages pressures implementations on small machines to process
+// plaintext without verifying the signature. This is very dangerous, and this API
+// discourages it, but a protocol that uses excessive message sizes might present
+// some implementations with no other choice.
+// 3. Performance may be improved by working with messages that fit into data caches.
+// Thus large amounts of data should be chunked so that each message is small.
+//
+// This package is not interoperable with the current release of NaCl
+// (https://nacl.cr.yp.to/sign.html), which does not support Ed25519 yet. However,
+// it is compatible with the NaCl fork libsodium (https://www.libsodium.org), as well
+// as TweetNaCl (https://tweetnacl.cr.yp.to/).
+package sign
+
+import (
+	"io"
+
+	"golang.org/x/crypto/ed25519"
+)
+
+// Overhead is the number of bytes of overhead when signing a message.
+const Overhead = 64
+
+// GenerateKey generates a new public/private key pair suitable for use with
+// Sign and Open.
+func GenerateKey(rand io.Reader) (publicKey *[32]byte, privateKey *[64]byte, err error) {
+	pub, priv, err := ed25519.GenerateKey(rand)
+	if err != nil {
+		return nil, nil, err
+	}
+	publicKey, privateKey = new([32]byte), new([64]byte)
+	copy((*publicKey)[:], pub)
+	copy((*privateKey)[:], priv)
+	return publicKey, privateKey, nil
+}
+
+// Sign appends a signed copy of message to out, which will be Overhead bytes
+// longer than the original and must not overlap it.
+func Sign(out, message []byte, privateKey *[64]byte) []byte {
+	sig := ed25519.Sign(ed25519.PrivateKey((*privateKey)[:]), message)
+	ret, out := sliceForAppend(out, Overhead+len(message))
+	copy(out, sig)
+	copy(out[Overhead:], message)
+	return ret
+}
+
+// Open verifies a signed message produced by Sign and appends the message to
+// out, which must not overlap the signed message. The output will be Overhead
+// bytes smaller than the signed message.
+func Open(out, signedMessage []byte, publicKey *[32]byte) ([]byte, bool) {
+	if len(signedMessage) < Overhead {
+		return nil, false
+	}
+	if !ed25519.Verify(ed25519.PublicKey((*publicKey)[:]), signedMessage[Overhead:], signedMessage[:Overhead]) {
+		return nil, false
+	}
+	ret, out := sliceForAppend(out, len(signedMessage)-Overhead)
+	copy(out, signedMessage[Overhead:])
+	return ret, true
+}
+
+// sliceForAppend takes a slice and a requested number of bytes. It returns a
+// slice with the contents of the given slice followed by that many bytes and a
+// second slice that aliases into it and contains only the extra bytes. If the
+// original slice has sufficient capacity then no allocation is performed.
+func sliceForAppend(in []byte, n int) (head, tail []byte) {
+	if total := len(in) + n; cap(in) >= total {
+		head = in[:total]
+	} else {
+		head = make([]byte, total)
+		copy(head, in)
+	}
+	tail = head[len(in):]
+	return
+}
diff --git a/nacl/sign/sign_test.go b/nacl/sign/sign_test.go
new file mode 100644
index 0000000..0a6439a
--- /dev/null
+++ b/nacl/sign/sign_test.go
@@ -0,0 +1,74 @@
+// Copyright 2018 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.
+
+package sign
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/hex"
+	"testing"
+)
+
+var testSignedMessage, _ = hex.DecodeString("26a0a47f733d02ddb74589b6cbd6f64a7dab1947db79395a1a9e00e4c902c0f185b119897b89b248d16bab4ea781b5a3798d25c2984aec833dddab57e0891e0d68656c6c6f20776f726c64")
+var testMessage = testSignedMessage[Overhead:]
+var testPublicKey [32]byte
+var testPrivateKey = [64]byte{
+	0x98, 0x3c, 0x6a, 0xa6, 0x21, 0xcc, 0xbb, 0xb2, 0xa7, 0xe8, 0x97, 0x94, 0xde, 0x5f, 0xf8, 0x11,
+	0x8a, 0xf3, 0x33, 0x1a, 0x03, 0x5c, 0x43, 0x99, 0x03, 0x13, 0x2d, 0xd7, 0xb4, 0xc4, 0x8b, 0xb0,
+	0xf6, 0x33, 0x20, 0xa3, 0x34, 0x8b, 0x7b, 0xe2, 0xfe, 0xb4, 0xe7, 0x3a, 0x54, 0x08, 0x2d, 0xd7,
+	0x0c, 0xb7, 0xc0, 0xe3, 0xbf, 0x62, 0x6c, 0x55, 0xf0, 0x33, 0x28, 0x52, 0xf8, 0x48, 0x7d, 0xfd,
+}
+
+func init() {
+	copy(testPublicKey[:], testPrivateKey[32:])
+}
+
+func TestSign(t *testing.T) {
+	signedMessage := Sign(nil, testMessage, &testPrivateKey)
+	if !bytes.Equal(signedMessage, testSignedMessage) {
+		t.Fatalf("signed message did not match, got\n%x\n, expected\n%x", signedMessage, testSignedMessage)
+	}
+}
+
+func TestOpen(t *testing.T) {
+	message, ok := Open(nil, testSignedMessage, &testPublicKey)
+	if !ok {
+		t.Fatalf("valid signed message not successfully verified")
+	}
+	if !bytes.Equal(message, testMessage) {
+		t.Fatalf("message did not match, got\n%x\n, expected\n%x", message, testMessage)
+	}
+	message, ok = Open(nil, testSignedMessage[1:], &testPublicKey)
+	if ok {
+		t.Fatalf("invalid signed message successfully verified")
+	}
+
+	badMessage := make([]byte, len(testSignedMessage))
+	copy(badMessage, testSignedMessage)
+	badMessage[5] ^= 1
+	if _, ok := Open(nil, badMessage, &testPublicKey); ok {
+		t.Fatalf("Open succeeded with a corrupt message")
+	}
+
+	var badPublicKey [32]byte
+	copy(badPublicKey[:], testPublicKey[:])
+	badPublicKey[5] ^= 1
+	if _, ok := Open(nil, testSignedMessage, &badPublicKey); ok {
+		t.Fatalf("Open succeeded with a corrupt public key")
+	}
+}
+
+func TestGenerateSignOpen(t *testing.T) {
+	publicKey, privateKey, _ := GenerateKey(rand.Reader)
+	signedMessage := Sign(nil, testMessage, privateKey)
+	message, ok := Open(nil, signedMessage, publicKey)
+	if !ok {
+		t.Fatalf("failed to verify signed message")
+	}
+
+	if !bytes.Equal(message, testMessage) {
+		t.Fatalf("verified message does not match signed messge, got\n%x\n, expected\n%x", message, testMessage)
+	}
+}