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