lib/crypto/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/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
  16 static 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 - 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  */
  76 void 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 }
  90 EXPORT_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  * @out: 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  */
 103 void 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 }
 114 EXPORT_SYMBOL(hchacha_block_generic);