+++ /dev/null
-// Copyright 2012 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 secretbox encrypts and authenticates small messages.
-
-Secretbox uses XSalsa20 and Poly1305 to encrypt and authenticate messages with
-secret-key cryptography. The length of messages is not hidden.
-
-It is the caller's responsibility to ensure the uniqueness of nonces—for
-example, by using nonce 1 for the first message, nonce 2 for the second
-message, etc. Nonces are long enough that randomly generated nonces have
-negligible risk of collision.
-
-This package is interoperable with NaCl: https://nacl.cr.yp.to/secretbox.html.
-*/
-package secretbox // import "golang.org/x/crypto/nacl/secretbox"
-
-import (
- "golang.org/x/crypto/poly1305"
- "golang.org/x/crypto/salsa20/salsa"
-)
-
-// Overhead is the number of bytes of overhead when boxing a message.
-const Overhead = poly1305.TagSize
-
-// setup produces a sub-key and Salsa20 counter given a nonce and key.
-func setup(subKey *[32]byte, counter *[16]byte, nonce *[24]byte, key *[32]byte) {
- // We use XSalsa20 for encryption so first we need to generate a
- // key and nonce with HSalsa20.
- var hNonce [16]byte
- copy(hNonce[:], nonce[:])
- salsa.HSalsa20(subKey, &hNonce, key, &salsa.Sigma)
-
- // The final 8 bytes of the original nonce form the new nonce.
- copy(counter[:], nonce[16:])
-}
-
-// 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
-}
-
-// Seal appends an encrypted and authenticated copy of message to out, which
-// must not overlap message. The key and nonce pair must be unique for each
-// distinct message and the output will be Overhead bytes longer than message.
-func Seal(out, message []byte, nonce *[24]byte, key *[32]byte) []byte {
- var subKey [32]byte
- var counter [16]byte
- setup(&subKey, &counter, nonce, key)
-
- // The Poly1305 key is generated by encrypting 32 bytes of zeros. Since
- // Salsa20 works with 64-byte blocks, we also generate 32 bytes of
- // keystream as a side effect.
- var firstBlock [64]byte
- salsa.XORKeyStream(firstBlock[:], firstBlock[:], &counter, &subKey)
-
- var poly1305Key [32]byte
- copy(poly1305Key[:], firstBlock[:])
-
- ret, out := sliceForAppend(out, len(message)+poly1305.TagSize)
-
- // We XOR up to 32 bytes of message with the keystream generated from
- // the first block.
- firstMessageBlock := message
- if len(firstMessageBlock) > 32 {
- firstMessageBlock = firstMessageBlock[:32]
- }
-
- tagOut := out
- out = out[poly1305.TagSize:]
- for i, x := range firstMessageBlock {
- out[i] = firstBlock[32+i] ^ x
- }
- message = message[len(firstMessageBlock):]
- ciphertext := out
- out = out[len(firstMessageBlock):]
-
- // Now encrypt the rest.
- counter[8] = 1
- salsa.XORKeyStream(out, message, &counter, &subKey)
-
- var tag [poly1305.TagSize]byte
- poly1305.Sum(&tag, ciphertext, &poly1305Key)
- copy(tagOut, tag[:])
-
- return ret
-}
-
-// Open authenticates and decrypts a box produced by Seal and appends the
-// message to out, which must not overlap box. The output will be Overhead
-// bytes smaller than box.
-func Open(out []byte, box []byte, nonce *[24]byte, key *[32]byte) ([]byte, bool) {
- if len(box) < Overhead {
- return nil, false
- }
-
- var subKey [32]byte
- var counter [16]byte
- setup(&subKey, &counter, nonce, key)
-
- // The Poly1305 key is generated by encrypting 32 bytes of zeros. Since
- // Salsa20 works with 64-byte blocks, we also generate 32 bytes of
- // keystream as a side effect.
- var firstBlock [64]byte
- salsa.XORKeyStream(firstBlock[:], firstBlock[:], &counter, &subKey)
-
- var poly1305Key [32]byte
- copy(poly1305Key[:], firstBlock[:])
- var tag [poly1305.TagSize]byte
- copy(tag[:], box)
-
- if !poly1305.Verify(&tag, box[poly1305.TagSize:], &poly1305Key) {
- return nil, false
- }
-
- ret, out := sliceForAppend(out, len(box)-Overhead)
-
- // We XOR up to 32 bytes of box with the keystream generated from
- // the first block.
- box = box[Overhead:]
- firstMessageBlock := box
- if len(firstMessageBlock) > 32 {
- firstMessageBlock = firstMessageBlock[:32]
- }
- for i, x := range firstMessageBlock {
- out[i] = firstBlock[32+i] ^ x
- }
-
- box = box[len(firstMessageBlock):]
- out = out[len(firstMessageBlock):]
-
- // Now decrypt the rest.
- counter[8] = 1
- salsa.XORKeyStream(out, box, &counter, &subKey)
-
- return ret, true
-}
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