1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
  4 *
  5 * Copyright (C) 2015 Martin Willi
  6 */
  7
  8#include <linux/bug.h>
  9#include <linux/kernel.h>
 10#include <linux/export.h>
 11#include <linux/bitops.h>
 12#include <linux/string.h>
 13#include <asm/unaligned.h>
 14#include <crypto/chacha.h>
 15
 16static void chacha_permute(u32 *x, int nrounds)
 17{
 18	int i;
 19
 20	/* whitelist the allowed round counts */
 21	WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
 22
 23	for (i = 0; i < nrounds; i += 2) {
 24		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],  16);
 25		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],  16);
 26		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],  16);
 27		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],  16);
 28
 29		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],  12);
 30		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],  12);
 31		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10], 12);
 32		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11], 12);
 33
 34		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],   8);
 35		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],   8);
 36		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],   8);
 37		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],   8);
 38
 39		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],   7);
 40		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],   7);
 41		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10],  7);
 42		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11],  7);
 43
 44		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],  16);
 45		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],  16);
 46		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],  16);
 47		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],  16);
 48
 49		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10], 12);
 50		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11], 12);
 51		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],  12);
 52		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],  12);
 53
 54		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],   8);
 55		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],   8);
 56		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],   8);
 57		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],   8);
 58
 59		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10],  7);
 60		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11],  7);
 61		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],   7);
 62		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],   7);
 63	}
 64}
 65
 66/**
 67 * chacha_block_generic - generate one keystream block and increment block counter
 68 * @state: input state matrix (16 32-bit words)
 69 * @stream: output keystream block (64 bytes)
 70 * @nrounds: number of rounds (20 or 12; 20 is recommended)
 71 *
 72 * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
 73 * The caller has already converted the endianness of the input.  This function
 74 * also handles incrementing the block counter in the input matrix.
 75 */
 76void chacha_block_generic(u32 *state, u8 *stream, int nrounds)
 77{
 78	u32 x[16];
 79	int i;
 80
 81	memcpy(x, state, 64);
 82
 83	chacha_permute(x, nrounds);
 84
 85	for (i = 0; i < ARRAY_SIZE(x); i++)
 86		put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
 87
 88	state[12]++;
 89}
 90EXPORT_SYMBOL(chacha_block_generic);
 91
 92/**
 93 * hchacha_block_generic - abbreviated ChaCha core, for XChaCha
 94 * @state: input state matrix (16 32-bit words)
 95 * @stream: output (8 32-bit words)
 96 * @nrounds: number of rounds (20 or 12; 20 is recommended)
 97 *
 98 * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
 99 * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf).  HChaCha
100 * skips the final addition of the initial state, and outputs only certain words
101 * of the state.  It should not be used for streaming directly.
102 */
103void hchacha_block_generic(const u32 *state, u32 *stream, int nrounds)
104{
105	u32 x[16];
106
107	memcpy(x, state, 64);
108
109	chacha_permute(x, nrounds);
110
111	memcpy(&stream[0], &x[0], 16);
112	memcpy(&stream[4], &x[12], 16);
113}
114EXPORT_SYMBOL(hchacha_block_generic);