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// 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 ChaCha20 implements the core ChaCha20 function as specified in https://tools.ietf.org/html/rfc7539#section-2.3.
package chacha20
import "encoding/binary"
const rounds = 20
// core applies the ChaCha20 core function to 16-byte input in, 32-byte key k,
// and 16-byte constant c, and puts the result into 64-byte array out.
func core(out *[64]byte, in *[16]byte, k *[32]byte) {
j0 := uint32(0x61707865)
j1 := uint32(0x3320646e)
j2 := uint32(0x79622d32)
j3 := uint32(0x6b206574)
j4 := binary.LittleEndian.Uint32(k[0:4])
j5 := binary.LittleEndian.Uint32(k[4:8])
j6 := binary.LittleEndian.Uint32(k[8:12])
j7 := binary.LittleEndian.Uint32(k[12:16])
j8 := binary.LittleEndian.Uint32(k[16:20])
j9 := binary.LittleEndian.Uint32(k[20:24])
j10 := binary.LittleEndian.Uint32(k[24:28])
j11 := binary.LittleEndian.Uint32(k[28:32])
j12 := binary.LittleEndian.Uint32(in[0:4])
j13 := binary.LittleEndian.Uint32(in[4:8])
j14 := binary.LittleEndian.Uint32(in[8:12])
j15 := binary.LittleEndian.Uint32(in[12:16])
x0, x1, x2, x3, x4, x5, x6, x7 := j0, j1, j2, j3, j4, j5, j6, j7
x8, x9, x10, x11, x12, x13, x14, x15 := j8, j9, j10, j11, j12, j13, j14, j15
for i := 0; i < rounds; i += 2 {
x0 += x4
x12 ^= x0
x12 = (x12 << 16) | (x12 >> (16))
x8 += x12
x4 ^= x8
x4 = (x4 << 12) | (x4 >> (20))
x0 += x4
x12 ^= x0
x12 = (x12 << 8) | (x12 >> (24))
x8 += x12
x4 ^= x8
x4 = (x4 << 7) | (x4 >> (25))
x1 += x5
x13 ^= x1
x13 = (x13 << 16) | (x13 >> 16)
x9 += x13
x5 ^= x9
x5 = (x5 << 12) | (x5 >> 20)
x1 += x5
x13 ^= x1
x13 = (x13 << 8) | (x13 >> 24)
x9 += x13
x5 ^= x9
x5 = (x5 << 7) | (x5 >> 25)
x2 += x6
x14 ^= x2
x14 = (x14 << 16) | (x14 >> 16)
x10 += x14
x6 ^= x10
x6 = (x6 << 12) | (x6 >> 20)
x2 += x6
x14 ^= x2
x14 = (x14 << 8) | (x14 >> 24)
x10 += x14
x6 ^= x10
x6 = (x6 << 7) | (x6 >> 25)
x3 += x7
x15 ^= x3
x15 = (x15 << 16) | (x15 >> 16)
x11 += x15
x7 ^= x11
x7 = (x7 << 12) | (x7 >> 20)
x3 += x7
x15 ^= x3
x15 = (x15 << 8) | (x15 >> 24)
x11 += x15
x7 ^= x11
x7 = (x7 << 7) | (x7 >> 25)
x0 += x5
x15 ^= x0
x15 = (x15 << 16) | (x15 >> 16)
x10 += x15
x5 ^= x10
x5 = (x5 << 12) | (x5 >> 20)
x0 += x5
x15 ^= x0
x15 = (x15 << 8) | (x15 >> 24)
x10 += x15
x5 ^= x10
x5 = (x5 << 7) | (x5 >> 25)
x1 += x6
x12 ^= x1
x12 = (x12 << 16) | (x12 >> 16)
x11 += x12
x6 ^= x11
x6 = (x6 << 12) | (x6 >> 20)
x1 += x6
x12 ^= x1
x12 = (x12 << 8) | (x12 >> 24)
x11 += x12
x6 ^= x11
x6 = (x6 << 7) | (x6 >> 25)
x2 += x7
x13 ^= x2
x13 = (x13 << 16) | (x13 >> 16)
x8 += x13
x7 ^= x8
x7 = (x7 << 12) | (x7 >> 20)
x2 += x7
x13 ^= x2
x13 = (x13 << 8) | (x13 >> 24)
x8 += x13
x7 ^= x8
x7 = (x7 << 7) | (x7 >> 25)
x3 += x4
x14 ^= x3
x14 = (x14 << 16) | (x14 >> 16)
x9 += x14
x4 ^= x9
x4 = (x4 << 12) | (x4 >> 20)
x3 += x4
x14 ^= x3
x14 = (x14 << 8) | (x14 >> 24)
x9 += x14
x4 ^= x9
x4 = (x4 << 7) | (x4 >> 25)
}
x0 += j0
x1 += j1
x2 += j2
x3 += j3
x4 += j4
x5 += j5
x6 += j6
x7 += j7
x8 += j8
x9 += j9
x10 += j10
x11 += j11
x12 += j12
x13 += j13
x14 += j14
x15 += j15
binary.LittleEndian.PutUint32(out[0:4], x0)
binary.LittleEndian.PutUint32(out[4:8], x1)
binary.LittleEndian.PutUint32(out[8:12], x2)
binary.LittleEndian.PutUint32(out[12:16], x3)
binary.LittleEndian.PutUint32(out[16:20], x4)
binary.LittleEndian.PutUint32(out[20:24], x5)
binary.LittleEndian.PutUint32(out[24:28], x6)
binary.LittleEndian.PutUint32(out[28:32], x7)
binary.LittleEndian.PutUint32(out[32:36], x8)
binary.LittleEndian.PutUint32(out[36:40], x9)
binary.LittleEndian.PutUint32(out[40:44], x10)
binary.LittleEndian.PutUint32(out[44:48], x11)
binary.LittleEndian.PutUint32(out[48:52], x12)
binary.LittleEndian.PutUint32(out[52:56], x13)
binary.LittleEndian.PutUint32(out[56:60], x14)
binary.LittleEndian.PutUint32(out[60:64], x15)
}
// XORKeyStream crypts bytes from in to out using the given key and counters.
// In and out must overlap entirely or not at all. Counter contains the raw
// ChaCha20 counter bytes (i.e. block counter followed by nonce).
func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
var block [64]byte
var counterCopy [16]byte
copy(counterCopy[:], counter[:])
for len(in) >= 64 {
core(&block, &counterCopy, key)
for i, x := range block {
out[i] = in[i] ^ x
}
u := uint32(1)
for i := 0; i < 4; i++ {
u += uint32(counterCopy[i])
counterCopy[i] = byte(u)
u >>= 8
}
in = in[64:]
out = out[64:]
}
if len(in) > 0 {
core(&block, &counterCopy, key)
for i, v := range in {
out[i] = v ^ block[i]
}
}
}
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