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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
*
* Copyright (C) 2015 Martin Willi
*/
#include <linux/bug.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/bitops.h>
#include <linux/string.h>
#include <linux/unaligned.h>
#include <crypto/chacha.h>
static void chacha_permute(struct chacha_state *state, int nrounds)
{
u32 *x = state->x;
int i;
/* whitelist the allowed round counts */
WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
for (i = 0; i < nrounds; i += 2) {
x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16);
x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16);
x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 16);
x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 16);
x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 12);
x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 12);
x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 12);
x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 12);
x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 8);
x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 8);
x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 8);
x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 8);
x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 7);
x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 7);
x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 7);
x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 7);
x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 16);
x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 16);
x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 16);
x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 16);
x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 12);
x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 12);
x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 12);
x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 12);
x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 8);
x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 8);
x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 8);
x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 8);
x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 7);
x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 7);
x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7);
x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7);
}
}
/**
* chacha_block_generic - generate one keystream block and increment block counter
* @state: input state matrix
* @out: output keystream block
* @nrounds: number of rounds (20 or 12; 20 is recommended)
*
* This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
* The caller has already converted the endianness of the input. This function
* also handles incrementing the block counter in the input matrix.
*/
void chacha_block_generic(struct chacha_state *state,
u8 out[CHACHA_BLOCK_SIZE], int nrounds)
{
struct chacha_state permuted_state = *state;
int i;
chacha_permute(&permuted_state, nrounds);
for (i = 0; i < ARRAY_SIZE(state->x); i++)
put_unaligned_le32(permuted_state.x[i] + state->x[i],
&out[i * sizeof(u32)]);
state->x[12]++;
}
EXPORT_SYMBOL(chacha_block_generic);
/**
* hchacha_block_generic - abbreviated ChaCha core, for XChaCha
* @state: input state matrix
* @out: the output words
* @nrounds: number of rounds (20 or 12; 20 is recommended)
*
* HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
* towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha
* skips the final addition of the initial state, and outputs only certain words
* of the state. It should not be used for streaming directly.
*/
void hchacha_block_generic(const struct chacha_state *state,
u32 out[HCHACHA_OUT_WORDS], int nrounds)
{
struct chacha_state permuted_state = *state;
chacha_permute(&permuted_state, nrounds);
memcpy(&out[0], &permuted_state.x[0], 16);
memcpy(&out[4], &permuted_state.x[12], 16);
}
EXPORT_SYMBOL(hchacha_block_generic);
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