71 lines
2.2 KiB
Go
71 lines
2.2 KiB
Go
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// 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/chacha20poly1305/internal/chacha20"
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"golang.org/x/crypto/poly1305"
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)
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func roundTo16(n int) int {
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return 16 * ((n + 15) / 16)
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}
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func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
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var counter [16]byte
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copy(counter[4:], nonce)
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var polyKey [32]byte
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chacha20.XORKeyStream(polyKey[:], polyKey[:], &counter, &c.key)
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ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
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counter[0] = 1
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chacha20.XORKeyStream(out, plaintext, &counter, &c.key)
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polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(plaintext))+8+8)
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copy(polyInput, additionalData)
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copy(polyInput[roundTo16(len(additionalData)):], out[:len(plaintext)])
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binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
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binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(plaintext)))
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var tag [poly1305.TagSize]byte
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poly1305.Sum(&tag, polyInput, &polyKey)
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copy(out[len(plaintext):], tag[:])
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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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var tag [poly1305.TagSize]byte
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copy(tag[:], ciphertext[len(ciphertext)-16:])
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ciphertext = ciphertext[:len(ciphertext)-16]
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var counter [16]byte
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copy(counter[4:], nonce)
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var polyKey [32]byte
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chacha20.XORKeyStream(polyKey[:], polyKey[:], &counter, &c.key)
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polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(ciphertext))+8+8)
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copy(polyInput, additionalData)
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copy(polyInput[roundTo16(len(additionalData)):], ciphertext)
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binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
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binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(ciphertext)))
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ret, out := sliceForAppend(dst, len(ciphertext))
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if !poly1305.Verify(&tag, polyInput, &polyKey) {
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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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counter[0] = 1
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chacha20.XORKeyStream(out, ciphertext, &counter, &c.key)
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return ret, nil
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}
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