Upgrading dependencies to include logrus.

vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305.go

@@ -0,0 +1,101 @@
+// Copyright 2016 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 chacha20poly1305 implements the ChaCha20-Poly1305 AEAD as specified in RFC 7539,
+// and its extended nonce variant XChaCha20-Poly1305.
+package chacha20poly1305 // import "golang.org/x/crypto/chacha20poly1305"
+
+import (
+	"crypto/cipher"
+	"encoding/binary"
+	"errors"
+)
+
+const (
+	// KeySize is the size of the key used by this AEAD, in bytes.
+	KeySize = 32
+
+	// NonceSize is the size of the nonce used with the standard variant of this
+	// AEAD, in bytes.
+	//
+	// Note that this is too short to be safely generated at random if the same
+	// key is reused more than 2³² times.
+	NonceSize = 12
+
+	// NonceSizeX is the size of the nonce used with the XChaCha20-Poly1305
+	// variant of this AEAD, in bytes.
+	NonceSizeX = 24
+)
+
+type chacha20poly1305 struct {
+	key [8]uint32
+}
+
+// New returns a ChaCha20-Poly1305 AEAD that uses the given 256-bit key.
+func New(key []byte) (cipher.AEAD, error) {
+	if len(key) != KeySize {
+		return nil, errors.New("chacha20poly1305: bad key length")
+	}
+	ret := new(chacha20poly1305)
+	ret.key[0] = binary.LittleEndian.Uint32(key[0:4])
+	ret.key[1] = binary.LittleEndian.Uint32(key[4:8])
+	ret.key[2] = binary.LittleEndian.Uint32(key[8:12])
+	ret.key[3] = binary.LittleEndian.Uint32(key[12:16])
+	ret.key[4] = binary.LittleEndian.Uint32(key[16:20])
+	ret.key[5] = binary.LittleEndian.Uint32(key[20:24])
+	ret.key[6] = binary.LittleEndian.Uint32(key[24:28])
+	ret.key[7] = binary.LittleEndian.Uint32(key[28:32])
+	return ret, nil
+}
+
+func (c *chacha20poly1305) NonceSize() int {
+	return NonceSize
+}
+
+func (c *chacha20poly1305) Overhead() int {
+	return 16
+}
+
+func (c *chacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
+	if len(nonce) != NonceSize {
+		panic("chacha20poly1305: bad nonce length passed to Seal")
+	}
+
+	if uint64(len(plaintext)) > (1<<38)-64 {
+		panic("chacha20poly1305: plaintext too large")
+	}
+
+	return c.seal(dst, nonce, plaintext, additionalData)
+}
+
+var errOpen = errors.New("chacha20poly1305: message authentication failed")
+
+func (c *chacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
+	if len(nonce) != NonceSize {
+		panic("chacha20poly1305: bad nonce length passed to Open")
+	}
+	if len(ciphertext) < 16 {
+		return nil, errOpen
+	}
+	if uint64(len(ciphertext)) > (1<<38)-48 {
+		panic("chacha20poly1305: ciphertext too large")
+	}
+
+	return c.open(dst, nonce, ciphertext, additionalData)
+}
+
+// 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
+}

vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.go

@@ -0,0 +1,86 @@
+// Copyright 2016 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.
+
+// +build go1.7,amd64,!gccgo,!appengine
+
+package chacha20poly1305
+
+import (
+	"encoding/binary"
+
+	"golang.org/x/crypto/internal/subtle"
+	"golang.org/x/sys/cpu"
+)
+
+//go:noescape
+func chacha20Poly1305Open(dst []byte, key []uint32, src, ad []byte) bool
+
+//go:noescape
+func chacha20Poly1305Seal(dst []byte, key []uint32, src, ad []byte)
+
+var (
+	useAVX2 = cpu.X86.HasAVX2 && cpu.X86.HasBMI2
+)
+
+// setupState writes a ChaCha20 input matrix to state. See
+// https://tools.ietf.org/html/rfc7539#section-2.3.
+func setupState(state *[16]uint32, key *[8]uint32, nonce []byte) {
+	state[0] = 0x61707865
+	state[1] = 0x3320646e
+	state[2] = 0x79622d32
+	state[3] = 0x6b206574
+
+	state[4] = key[0]
+	state[5] = key[1]
+	state[6] = key[2]
+	state[7] = key[3]
+	state[8] = key[4]
+	state[9] = key[5]
+	state[10] = key[6]
+	state[11] = key[7]
+
+	state[12] = 0
+	state[13] = binary.LittleEndian.Uint32(nonce[:4])
+	state[14] = binary.LittleEndian.Uint32(nonce[4:8])
+	state[15] = binary.LittleEndian.Uint32(nonce[8:12])
+}
+
+func (c *chacha20poly1305) seal(dst, nonce, plaintext, additionalData []byte) []byte {
+	if !cpu.X86.HasSSSE3 {
+		return c.sealGeneric(dst, nonce, plaintext, additionalData)
+	}
+
+	var state [16]uint32
+	setupState(&state, &c.key, nonce)
+
+	ret, out := sliceForAppend(dst, len(plaintext)+16)
+	if subtle.InexactOverlap(out, plaintext) {
+		panic("chacha20poly1305: invalid buffer overlap")
+	}
+	chacha20Poly1305Seal(out[:], state[:], plaintext, additionalData)
+	return ret
+}
+
+func (c *chacha20poly1305) open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
+	if !cpu.X86.HasSSSE3 {
+		return c.openGeneric(dst, nonce, ciphertext, additionalData)
+	}
+
+	var state [16]uint32
+	setupState(&state, &c.key, nonce)
+
+	ciphertext = ciphertext[:len(ciphertext)-16]
+	ret, out := sliceForAppend(dst, len(ciphertext))
+	if subtle.InexactOverlap(out, ciphertext) {
+		panic("chacha20poly1305: invalid buffer overlap")
+	}
+	if !chacha20Poly1305Open(out, state[:], ciphertext, additionalData) {
+		for i := range out {
+			out[i] = 0
+		}
+		return nil, errOpen
+	}
+
+	return ret, nil
+}

vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_generic.go

@@ -0,0 +1,81 @@
+// Copyright 2016 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 chacha20poly1305
+
+import (
+	"encoding/binary"
+
+	"golang.org/x/crypto/internal/chacha20"
+	"golang.org/x/crypto/internal/subtle"
+	"golang.org/x/crypto/poly1305"
+)
+
+func roundTo16(n int) int {
+	return 16 * ((n + 15) / 16)
+}
+
+func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
+	ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
+	if subtle.InexactOverlap(out, plaintext) {
+		panic("chacha20poly1305: invalid buffer overlap")
+	}
+
+	var polyKey [32]byte
+	s := chacha20.New(c.key, [3]uint32{
+		binary.LittleEndian.Uint32(nonce[0:4]),
+		binary.LittleEndian.Uint32(nonce[4:8]),
+		binary.LittleEndian.Uint32(nonce[8:12]),
+	})
+	s.XORKeyStream(polyKey[:], polyKey[:])
+	s.Advance() // skip the next 32 bytes
+	s.XORKeyStream(out, plaintext)
+
+	polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(plaintext))+8+8)
+	copy(polyInput, additionalData)
+	copy(polyInput[roundTo16(len(additionalData)):], out[:len(plaintext)])
+	binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
+	binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(plaintext)))
+
+	var tag [poly1305.TagSize]byte
+	poly1305.Sum(&tag, polyInput, &polyKey)
+	copy(out[len(plaintext):], tag[:])
+
+	return ret
+}
+
+func (c *chacha20poly1305) openGeneric(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
+	var tag [poly1305.TagSize]byte
+	copy(tag[:], ciphertext[len(ciphertext)-16:])
+	ciphertext = ciphertext[:len(ciphertext)-16]
+
+	var polyKey [32]byte
+	s := chacha20.New(c.key, [3]uint32{
+		binary.LittleEndian.Uint32(nonce[0:4]),
+		binary.LittleEndian.Uint32(nonce[4:8]),
+		binary.LittleEndian.Uint32(nonce[8:12]),
+	})
+	s.XORKeyStream(polyKey[:], polyKey[:])
+	s.Advance() // skip the next 32 bytes
+
+	polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(ciphertext))+8+8)
+	copy(polyInput, additionalData)
+	copy(polyInput[roundTo16(len(additionalData)):], ciphertext)
+	binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
+	binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(ciphertext)))
+
+	ret, out := sliceForAppend(dst, len(ciphertext))
+	if subtle.InexactOverlap(out, ciphertext) {
+		panic("chacha20poly1305: invalid buffer overlap")
+	}
+	if !poly1305.Verify(&tag, polyInput, &polyKey) {
+		for i := range out {
+			out[i] = 0
+		}
+		return nil, errOpen
+	}
+
+	s.XORKeyStream(out, ciphertext)
+	return ret, nil
+}

vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_noasm.go

@@ -0,0 +1,15 @@
+// Copyright 2016 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.
+
+// +build !amd64 !go1.7 gccgo appengine
+
+package chacha20poly1305
+
+func (c *chacha20poly1305) seal(dst, nonce, plaintext, additionalData []byte) []byte {
+	return c.sealGeneric(dst, nonce, plaintext, additionalData)
+}
+
+func (c *chacha20poly1305) open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
+	return c.openGeneric(dst, nonce, ciphertext, additionalData)
+}

vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_test.go

@@ -0,0 +1,255 @@
+// Copyright 2016 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 chacha20poly1305
+
+import (
+	"bytes"
+	"crypto/cipher"
+	cryptorand "crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"log"
+	mathrand "math/rand"
+	"strconv"
+	"testing"
+)
+
+func TestVectors(t *testing.T) {
+	for i, test := range chacha20Poly1305Tests {
+		key, _ := hex.DecodeString(test.key)
+		nonce, _ := hex.DecodeString(test.nonce)
+		ad, _ := hex.DecodeString(test.aad)
+		plaintext, _ := hex.DecodeString(test.plaintext)
+
+		var (
+			aead cipher.AEAD
+			err  error
+		)
+		switch len(nonce) {
+		case NonceSize:
+			aead, err = New(key)
+		case NonceSizeX:
+			aead, err = NewX(key)
+		default:
+			t.Fatalf("#%d: wrong nonce length: %d", i, len(nonce))
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		ct := aead.Seal(nil, nonce, plaintext, ad)
+		if ctHex := hex.EncodeToString(ct); ctHex != test.out {
+			t.Errorf("#%d: got %s, want %s", i, ctHex, test.out)
+			continue
+		}
+
+		plaintext2, err := aead.Open(nil, nonce, ct, ad)
+		if err != nil {
+			t.Errorf("#%d: Open failed", i)
+			continue
+		}
+
+		if !bytes.Equal(plaintext, plaintext2) {
+			t.Errorf("#%d: plaintext's don't match: got %x vs %x", i, plaintext2, plaintext)
+			continue
+		}
+
+		if len(ad) > 0 {
+			alterAdIdx := mathrand.Intn(len(ad))
+			ad[alterAdIdx] ^= 0x80
+			if _, err := aead.Open(nil, nonce, ct, ad); err == nil {
+				t.Errorf("#%d: Open was successful after altering additional data", i)
+			}
+			ad[alterAdIdx] ^= 0x80
+		}
+
+		alterNonceIdx := mathrand.Intn(aead.NonceSize())
+		nonce[alterNonceIdx] ^= 0x80
+		if _, err := aead.Open(nil, nonce, ct, ad); err == nil {
+			t.Errorf("#%d: Open was successful after altering nonce", i)
+		}
+		nonce[alterNonceIdx] ^= 0x80
+
+		alterCtIdx := mathrand.Intn(len(ct))
+		ct[alterCtIdx] ^= 0x80
+		if _, err := aead.Open(nil, nonce, ct, ad); err == nil {
+			t.Errorf("#%d: Open was successful after altering ciphertext", i)
+		}
+		ct[alterCtIdx] ^= 0x80
+	}
+}
+
+func TestRandom(t *testing.T) {
+	// Some random tests to verify Open(Seal) == Plaintext
+	f := func(t *testing.T, nonceSize int) {
+		for i := 0; i < 256; i++ {
+			var nonce = make([]byte, nonceSize)
+			var key [32]byte
+
+			al := mathrand.Intn(128)
+			pl := mathrand.Intn(16384)
+			ad := make([]byte, al)
+			plaintext := make([]byte, pl)
+			cryptorand.Read(key[:])
+			cryptorand.Read(nonce[:])
+			cryptorand.Read(ad)
+			cryptorand.Read(plaintext)
+
+			var (
+				aead cipher.AEAD
+				err  error
+			)
+			switch len(nonce) {
+			case NonceSize:
+				aead, err = New(key[:])
+			case NonceSizeX:
+				aead, err = NewX(key[:])
+			default:
+				t.Fatalf("#%d: wrong nonce length: %d", i, len(nonce))
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			ct := aead.Seal(nil, nonce[:], plaintext, ad)
+
+			plaintext2, err := aead.Open(nil, nonce[:], ct, ad)
+			if err != nil {
+				t.Errorf("Random #%d: Open failed", i)
+				continue
+			}
+
+			if !bytes.Equal(plaintext, plaintext2) {
+				t.Errorf("Random #%d: plaintext's don't match: got %x vs %x", i, plaintext2, plaintext)
+				continue
+			}
+
+			if len(ad) > 0 {
+				alterAdIdx := mathrand.Intn(len(ad))
+				ad[alterAdIdx] ^= 0x80
+				if _, err := aead.Open(nil, nonce[:], ct, ad); err == nil {
+					t.Errorf("Random #%d: Open was successful after altering additional data", i)
+				}
+				ad[alterAdIdx] ^= 0x80
+			}
+
+			alterNonceIdx := mathrand.Intn(aead.NonceSize())
+			nonce[alterNonceIdx] ^= 0x80
+			if _, err := aead.Open(nil, nonce[:], ct, ad); err == nil {
+				t.Errorf("Random #%d: Open was successful after altering nonce", i)
+			}
+			nonce[alterNonceIdx] ^= 0x80
+
+			alterCtIdx := mathrand.Intn(len(ct))
+			ct[alterCtIdx] ^= 0x80
+			if _, err := aead.Open(nil, nonce[:], ct, ad); err == nil {
+				t.Errorf("Random #%d: Open was successful after altering ciphertext", i)
+			}
+			ct[alterCtIdx] ^= 0x80
+		}
+	}
+	t.Run("Standard", func(t *testing.T) { f(t, NonceSize) })
+	t.Run("X", func(t *testing.T) { f(t, NonceSizeX) })
+}
+
+func benchamarkChaCha20Poly1305Seal(b *testing.B, buf []byte, nonceSize int) {
+	b.ReportAllocs()
+	b.SetBytes(int64(len(buf)))
+
+	var key [32]byte
+	var nonce = make([]byte, nonceSize)
+	var ad [13]byte
+	var out []byte
+
+	var aead cipher.AEAD
+	switch len(nonce) {
+	case NonceSize:
+		aead, _ = New(key[:])
+	case NonceSizeX:
+		aead, _ = NewX(key[:])
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		out = aead.Seal(out[:0], nonce[:], buf[:], ad[:])
+	}
+}
+
+func benchamarkChaCha20Poly1305Open(b *testing.B, buf []byte, nonceSize int) {
+	b.ReportAllocs()
+	b.SetBytes(int64(len(buf)))
+
+	var key [32]byte
+	var nonce = make([]byte, nonceSize)
+	var ad [13]byte
+	var ct []byte
+	var out []byte
+
+	var aead cipher.AEAD
+	switch len(nonce) {
+	case NonceSize:
+		aead, _ = New(key[:])
+	case NonceSizeX:
+		aead, _ = NewX(key[:])
+	}
+	ct = aead.Seal(ct[:0], nonce[:], buf[:], ad[:])
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		out, _ = aead.Open(out[:0], nonce[:], ct[:], ad[:])
+	}
+}
+
+func BenchmarkChacha20Poly1305(b *testing.B) {
+	for _, length := range []int{64, 1350, 8 * 1024} {
+		b.Run("Open-"+strconv.Itoa(length), func(b *testing.B) {
+			benchamarkChaCha20Poly1305Open(b, make([]byte, length), NonceSize)
+		})
+		b.Run("Seal-"+strconv.Itoa(length), func(b *testing.B) {
+			benchamarkChaCha20Poly1305Seal(b, make([]byte, length), NonceSize)
+		})
+
+		b.Run("Open-"+strconv.Itoa(length)+"-X", func(b *testing.B) {
+			benchamarkChaCha20Poly1305Open(b, make([]byte, length), NonceSizeX)
+		})
+		b.Run("Seal-"+strconv.Itoa(length)+"-X", func(b *testing.B) {
+			benchamarkChaCha20Poly1305Seal(b, make([]byte, length), NonceSizeX)
+		})
+	}
+}
+
+var key = make([]byte, KeySize)
+
+func ExampleNewX() {
+	aead, err := NewX(key)
+	if err != nil {
+		log.Fatalln("Failed to instantiate XChaCha20-Poly1305:", err)
+	}
+
+	for _, msg := range []string{
+		"Attack at dawn.",
+		"The eagle has landed.",
+		"Gophers, gophers, gophers everywhere!",
+	} {
+		// Encryption.
+		nonce := make([]byte, NonceSizeX)
+		if _, err := cryptorand.Read(nonce); err != nil {
+			panic(err)
+		}
+		ciphertext := aead.Seal(nil, nonce, []byte(msg), nil)
+
+		// Decryption.
+		plaintext, err := aead.Open(nil, nonce, ciphertext, nil)
+		if err != nil {
+			log.Fatalln("Failed to decrypt or authenticate message:", err)
+		}
+
+		fmt.Printf("%s\n", plaintext)
+	}
+
+	// Output: Attack at dawn.
+	// The eagle has landed.
+	// Gophers, gophers, gophers everywhere!
+}

vendor/golang.org/x/crypto/chacha20poly1305/xchacha20poly1305.go

@@ -0,0 +1,104 @@
+// 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 chacha20poly1305
+
+import (
+	"crypto/cipher"
+	"encoding/binary"
+	"errors"
+
+	"golang.org/x/crypto/internal/chacha20"
+)
+
+type xchacha20poly1305 struct {
+	key [8]uint32
+}
+
+// NewX returns a XChaCha20-Poly1305 AEAD that uses the given 256-bit key.
+//
+// XChaCha20-Poly1305 is a ChaCha20-Poly1305 variant that takes a longer nonce,
+// suitable to be generated randomly without risk of collisions. It should be
+// preferred when nonce uniqueness cannot be trivially ensured, or whenever
+// nonces are randomly generated.
+func NewX(key []byte) (cipher.AEAD, error) {
+	if len(key) != KeySize {
+		return nil, errors.New("chacha20poly1305: bad key length")
+	}
+	ret := new(xchacha20poly1305)
+	ret.key[0] = binary.LittleEndian.Uint32(key[0:4])
+	ret.key[1] = binary.LittleEndian.Uint32(key[4:8])
+	ret.key[2] = binary.LittleEndian.Uint32(key[8:12])
+	ret.key[3] = binary.LittleEndian.Uint32(key[12:16])
+	ret.key[4] = binary.LittleEndian.Uint32(key[16:20])
+	ret.key[5] = binary.LittleEndian.Uint32(key[20:24])
+	ret.key[6] = binary.LittleEndian.Uint32(key[24:28])
+	ret.key[7] = binary.LittleEndian.Uint32(key[28:32])
+	return ret, nil
+}
+
+func (*xchacha20poly1305) NonceSize() int {
+	return NonceSizeX
+}
+
+func (*xchacha20poly1305) Overhead() int {
+	return 16
+}
+
+func (x *xchacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
+	if len(nonce) != NonceSizeX {
+		panic("chacha20poly1305: bad nonce length passed to Seal")
+	}
+
+	// XChaCha20-Poly1305 technically supports a 64-bit counter, so there is no
+	// size limit. However, since we reuse the ChaCha20-Poly1305 implementation,
+	// the second half of the counter is not available. This is unlikely to be
+	// an issue because the cipher.AEAD API requires the entire message to be in
+	// memory, and the counter overflows at 256 GB.
+	if uint64(len(plaintext)) > (1<<38)-64 {
+		panic("chacha20poly1305: plaintext too large")
+	}
+
+	hNonce := [4]uint32{
+		binary.LittleEndian.Uint32(nonce[0:4]),
+		binary.LittleEndian.Uint32(nonce[4:8]),
+		binary.LittleEndian.Uint32(nonce[8:12]),
+		binary.LittleEndian.Uint32(nonce[12:16]),
+	}
+	c := &chacha20poly1305{
+		key: chacha20.HChaCha20(&x.key, &hNonce),
+	}
+	// The first 4 bytes of the final nonce are unused counter space.
+	cNonce := make([]byte, NonceSize)
+	copy(cNonce[4:12], nonce[16:24])
+
+	return c.seal(dst, cNonce[:], plaintext, additionalData)
+}
+
+func (x *xchacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
+	if len(nonce) != NonceSizeX {
+		panic("chacha20poly1305: bad nonce length passed to Open")
+	}
+	if len(ciphertext) < 16 {
+		return nil, errOpen
+	}
+	if uint64(len(ciphertext)) > (1<<38)-48 {
+		panic("chacha20poly1305: ciphertext too large")
+	}
+
+	hNonce := [4]uint32{
+		binary.LittleEndian.Uint32(nonce[0:4]),
+		binary.LittleEndian.Uint32(nonce[4:8]),
+		binary.LittleEndian.Uint32(nonce[8:12]),
+		binary.LittleEndian.Uint32(nonce[12:16]),
+	}
+	c := &chacha20poly1305{
+		key: chacha20.HChaCha20(&x.key, &hNonce),
+	}
+	// The first 4 bytes of the final nonce are unused counter space.
+	cNonce := make([]byte, NonceSize)
+	copy(cNonce[4:12], nonce[16:24])
+
+	return c.open(dst, cNonce[:], ciphertext, additionalData)
+}