85c2beccaf
New() -> NewAES256GCM() Also add missing NewChacha20poly1305 constructor in without_openssl.go.
118 lines
3.5 KiB
Go
118 lines
3.5 KiB
Go
// +build !without_openssl
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// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//
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// Copied from
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// https://github.com/golang/crypto/blob/32db794688a5a24a23a43f2a984cecd5b3d8da58/chacha20poly1305/xchacha20poly1305.go
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// and adapted for stupidgcm by @rfjakob.
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package stupidgcm
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import (
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"crypto/cipher"
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"errors"
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"log"
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"golang.org/x/crypto/chacha20"
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"golang.org/x/crypto/chacha20poly1305"
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)
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type stupidXchacha20poly1305 struct {
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// array instead of byte slice like
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// `struct xchacha20poly1305` in x/crypto/chacha20poly1305
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key [chacha20poly1305.KeySize]byte
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wiped bool
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}
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// NewXchacha20poly1305 returns a XChaCha20-Poly1305 cipher that satisfied the
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// cipher.AEAD interface.
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//
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// XChaCha20-Poly1305 is a ChaCha20-Poly1305 variant that takes a longer nonce,
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// suitable to be generated randomly without risk of collisions. It should be
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// preferred when nonce uniqueness cannot be trivially ensured, or whenever
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// nonces are randomly generated.
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//
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// Only 32-bytes keys and 24-byte IVs are supported.
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func NewXchacha20poly1305(key []byte) cipher.AEAD {
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if len(key) != chacha20poly1305.KeySize {
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log.Panic("bad key length")
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}
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ret := new(stupidXchacha20poly1305)
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copy(ret.key[:], key)
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return ret
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}
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func (*stupidXchacha20poly1305) NonceSize() int {
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return chacha20poly1305.NonceSizeX
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}
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func (*stupidXchacha20poly1305) Overhead() int {
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return tagLen
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}
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func (x *stupidXchacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
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if x.wiped {
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log.Panic("BUG: tried to use wiped key")
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}
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if len(nonce) != chacha20poly1305.NonceSizeX {
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log.Panic("bad nonce length passed to Seal")
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}
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// XChaCha20-Poly1305 technically supports a 64-bit counter, so there is no
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// size limit. However, since we reuse the ChaCha20-Poly1305 implementation,
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// the second half of the counter is not available. This is unlikely to be
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// an issue because the cipher.AEAD API requires the entire message to be in
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// memory, and the counter overflows at 256 GB.
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if uint64(len(plaintext)) > (1<<38)-64 {
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log.Panic("plaintext too large")
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}
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hKey, _ := chacha20.HChaCha20(x.key[:], nonce[0:16])
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c := NewChacha20poly1305(hKey).(*stupidChacha20poly1305)
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defer c.Wipe()
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// The first 4 bytes of the final nonce are unused counter space.
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cNonce := make([]byte, chacha20poly1305.NonceSize)
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copy(cNonce[4:12], nonce[16:24])
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return c.Seal(dst, cNonce[:], plaintext, additionalData)
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}
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func (x *stupidXchacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
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if x.wiped {
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log.Panic("BUG: tried to use wiped key")
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}
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if len(nonce) != chacha20poly1305.NonceSizeX {
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log.Panic("bad nonce length passed to Open")
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}
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if len(ciphertext) < 16 {
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return nil, errors.New("message too short")
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}
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if uint64(len(ciphertext)) > (1<<38)-48 {
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log.Panic("ciphertext too large")
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}
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hKey, _ := chacha20.HChaCha20(x.key[:], nonce[0:16])
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c := NewChacha20poly1305(hKey).(*stupidChacha20poly1305)
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defer c.Wipe()
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// The first 4 bytes of the final nonce are unused counter space.
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cNonce := make([]byte, chacha20poly1305.NonceSize)
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copy(cNonce[4:12], nonce[16:24])
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return c.Open(dst, cNonce[:], ciphertext, additionalData)
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}
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// Wipe tries to wipe the key from memory by overwriting it with zeros.
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//
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// This is not bulletproof due to possible GC copies, but
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// still raises the bar for extracting the key.
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func (g *stupidXchacha20poly1305) Wipe() {
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g.wiped = true
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for i := range g.key {
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g.key[i] = 0
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}
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}
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