82 lines
2.1 KiB
Go
82 lines
2.1 KiB
Go
// Copyright 2016 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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package chacha20poly1305
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import (
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"encoding/binary"
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"golang.org/x/crypto/chacha20"
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"golang.org/x/crypto/internal/subtle"
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"golang.org/x/crypto/poly1305"
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)
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func writeWithPadding(p *poly1305.MAC, b []byte) {
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p.Write(b)
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if rem := len(b) % 16; rem != 0 {
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var buf [16]byte
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padLen := 16 - rem
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p.Write(buf[:padLen])
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}
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}
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func writeUint64(p *poly1305.MAC, n int) {
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var buf [8]byte
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binary.LittleEndian.PutUint64(buf[:], uint64(n))
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p.Write(buf[:])
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}
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func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
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ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
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ciphertext, tag := out[:len(plaintext)], out[len(plaintext):]
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if subtle.InexactOverlap(out, plaintext) {
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panic("chacha20poly1305: invalid buffer overlap")
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}
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var polyKey [32]byte
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s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
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s.XORKeyStream(polyKey[:], polyKey[:])
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s.SetCounter(1) // set the counter to 1, skipping 32 bytes
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s.XORKeyStream(ciphertext, plaintext)
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p := poly1305.New(&polyKey)
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writeWithPadding(p, additionalData)
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writeWithPadding(p, ciphertext)
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writeUint64(p, len(additionalData))
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writeUint64(p, len(plaintext))
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p.Sum(tag[:0])
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return ret
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}
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func (c *chacha20poly1305) openGeneric(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
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tag := ciphertext[len(ciphertext)-16:]
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ciphertext = ciphertext[:len(ciphertext)-16]
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var polyKey [32]byte
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s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
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s.XORKeyStream(polyKey[:], polyKey[:])
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s.SetCounter(1) // set the counter to 1, skipping 32 bytes
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p := poly1305.New(&polyKey)
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writeWithPadding(p, additionalData)
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writeWithPadding(p, ciphertext)
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writeUint64(p, len(additionalData))
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writeUint64(p, len(ciphertext))
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ret, out := sliceForAppend(dst, len(ciphertext))
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if subtle.InexactOverlap(out, ciphertext) {
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panic("chacha20poly1305: invalid buffer overlap")
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}
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if !p.Verify(tag) {
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for i := range out {
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out[i] = 0
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}
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return nil, errOpen
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}
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s.XORKeyStream(out, ciphertext)
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return ret, nil
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}
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