lib/chacha.c

   1 /*
   2  * The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
   3  *
   4  * Copyright (C) 2015 Martin Willi
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  */
  11
  12 #include <linux/kernel.h>
  13 #include <linux/export.h>
  14 #include <linux/bitops.h>
  15 #include <linux/cryptohash.h>
  16 #include <asm/unaligned.h>
  17 #include <crypto/chacha.h>
  18
  19 static void chacha_permute(u32 *x, int nrounds)
  20 {
  21         int i;
  22
  23         /* whitelist the allowed round counts */
  24         WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
  25
  26         for (i = 0; i < nrounds; i += 2) {
  27                 x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],  16);
  28                 x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],  16);
  29                 x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],  16);
  30                 x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],  16);
  31
  32                 x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],  12);
  33                 x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],  12);
  34                 x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10], 12);
  35                 x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11], 12);
  36
  37                 x[0]  += x[4];    x[12] = rol32(x[12] ^ x[0],   8);
  38                 x[1]  += x[5];    x[13] = rol32(x[13] ^ x[1],   8);
  39                 x[2]  += x[6];    x[14] = rol32(x[14] ^ x[2],   8);
  40                 x[3]  += x[7];    x[15] = rol32(x[15] ^ x[3],   8);
  41
  42                 x[8]  += x[12];   x[4]  = rol32(x[4]  ^ x[8],   7);
  43                 x[9]  += x[13];   x[5]  = rol32(x[5]  ^ x[9],   7);
  44                 x[10] += x[14];   x[6]  = rol32(x[6]  ^ x[10],  7);
  45                 x[11] += x[15];   x[7]  = rol32(x[7]  ^ x[11],  7);
  46
  47                 x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],  16);
  48                 x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],  16);
  49                 x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],  16);
  50                 x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],  16);
  51
  52                 x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10], 12);
  53                 x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11], 12);
  54                 x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],  12);
  55                 x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],  12);
  56
  57                 x[0]  += x[5];    x[15] = rol32(x[15] ^ x[0],   8);
  58                 x[1]  += x[6];    x[12] = rol32(x[12] ^ x[1],   8);
  59                 x[2]  += x[7];    x[13] = rol32(x[13] ^ x[2],   8);
  60                 x[3]  += x[4];    x[14] = rol32(x[14] ^ x[3],   8);
  61
  62                 x[10] += x[15];   x[5]  = rol32(x[5]  ^ x[10],  7);
  63                 x[11] += x[12];   x[6]  = rol32(x[6]  ^ x[11],  7);
  64                 x[8]  += x[13];   x[7]  = rol32(x[7]  ^ x[8],   7);
  65                 x[9]  += x[14];   x[4]  = rol32(x[4]  ^ x[9],   7);
  66         }
  67 }
  68
  69 /**
  70  * chacha_block - generate one keystream block and increment block counter
  71  * @state: input state matrix (16 32-bit words)
  72  * @stream: output keystream block (64 bytes)
  73  * @nrounds: number of rounds (20 or 12; 20 is recommended)
  74  *
  75  * This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
  76  * The caller has already converted the endianness of the input.  This function
  77  * also handles incrementing the block counter in the input matrix.
  78  */
  79 void chacha_block(u32 *state, u8 *stream, int nrounds)
  80 {
  81         u32 x[16];
  82         int i;
  83
  84         memcpy(x, state, 64);
  85
  86         chacha_permute(x, nrounds);
  87
  88         for (i = 0; i < ARRAY_SIZE(x); i++)
  89                 put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
  90
  91         state[12]++;
  92 }
  93 EXPORT_SYMBOL(chacha_block);
  94
  95 /**
  96  * hchacha_block - abbreviated ChaCha core, for XChaCha
  97  * @in: input state matrix (16 32-bit words)
  98  * @out: output (8 32-bit 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  */
 106 void hchacha_block(const u32 *in, u32 *out, int nrounds)
 107 {
 108         u32 x[16];
 109
 110         memcpy(x, in, 64);
 111
 112         chacha_permute(x, nrounds);
 113
 114         memcpy(&out[0], &x[0], 16);
 115         memcpy(&out[4], &x[12], 16);
 116 }
 117 EXPORT_SYMBOL(hchacha_block);