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
  15 static 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  */
  75 void 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 }
  89 EXPORT_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  */
 102 void 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 }
 113 EXPORT_SYMBOL(hchacha_block);