chacha-block-generic.c

  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 <crypto/chacha.h>
  9#include <linux/bitops.h>
 10#include <linux/bug.h>
 11#include <linux/export.h>
 12#include <linux/kernel.h>
 13#include <linux/string.h>
 14#include <linux/unaligned.h>
 15
 16static void chacha_permute(struct chacha_state *state, int nrounds)
 17{
 18	u32 *x = state->x;
 19	int i;
 20
 21	/* whitelist the allowed round counts */
 22	WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
 23
 24	for (i = 0; i < nrounds; i += 2) {
 25		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],  16);
 26		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],  16);
 27		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],  16);
 28		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],  16);
 29
 30		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],  12);
 31		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],  12);
 32		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10], 12);
 33		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11], 12);
 34
 35		x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],   8);
 36		x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],   8);
 37		x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],   8);
 38		x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],   8);
 39
 40		x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],   7);
 41		x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],   7);
 42		x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10],  7);
 43		x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11],  7);
 44
 45		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],  16);
 46		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],  16);
 47		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],  16);
 48		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],  16);
 49
 50		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10], 12);
 51		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11], 12);
 52		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],  12);
 53		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],  12);
 54
 55		x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],   8);
 56		x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],   8);
 57		x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],   8);
 58		x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],   8);
 59
 60		x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10],  7);
 61		x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11],  7);
 62		x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],   7);
 63		x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],   7);
 64	}
 65}
 66
 67/**
 68 * chacha_block_generic - generate one keystream block and increment block counter
 69 * @state: input state matrix
 70 * @out: output keystream block
 71 * @nrounds: number of rounds (20 or 12; 20 is recommended)
 72 *
 73 * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
 74 * The caller has already converted the endianness of the input.  This function
 75 * also handles incrementing the block counter in the input matrix.
 76 */
 77void chacha_block_generic(struct chacha_state *state,
 78			  u8 out[CHACHA_BLOCK_SIZE], int nrounds)
 79{
 80	struct chacha_state permuted_state = *state;
 81	int i;
 82
 83	chacha_permute(&permuted_state, nrounds);
 84
 85	for (i = 0; i < ARRAY_SIZE(state->x); i++)
 86		put_unaligned_le32(permuted_state.x[i] + state->x[i],
 87				   &out[i * sizeof(u32)]);
 88
 89	state->x[12]++;
 90
 91	chacha_zeroize_state(&permuted_state);
 92}
 93EXPORT_SYMBOL(chacha_block_generic);
 94
 95/**
 96 * hchacha_block_generic - abbreviated ChaCha core, for XChaCha
 97 * @state: input state matrix
 98 * @out: the output words
 99 * @nrounds: number of rounds (20 or 12; 20 is recommended)
100 *
101 * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
102 * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf).  HChaCha
103 * skips the final addition of the initial state, and outputs only certain words
104 * of the state.  It should not be used for streaming directly.
105 */
106void hchacha_block_generic(const struct chacha_state *state,
107			   u32 out[HCHACHA_OUT_WORDS], int nrounds)
108{
109	struct chacha_state permuted_state = *state;
110
111	chacha_permute(&permuted_state, nrounds);
112
113	memcpy(&out[0], &permuted_state.x[0], 16);
114	memcpy(&out[4], &permuted_state.x[12], 16);
115
116	chacha_zeroize_state(&permuted_state);
117}
118EXPORT_SYMBOL(hchacha_block_generic);