120 lines
3.9 KiB
C
120 lines
3.9 KiB
C
/*
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* The "hash function" used as the core of the ChaCha stream cipher (RFC7539)
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*
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* Copyright (C) 2015 Martin Willi
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*/
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#include <linux/bug.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/bitops.h>
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#include <linux/string.h>
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#include <linux/cryptohash.h>
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#include <asm/unaligned.h>
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#include <crypto/chacha.h>
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static void chacha_permute(u32 *x, int nrounds)
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{
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int i;
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/* whitelist the allowed round counts */
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WARN_ON_ONCE(nrounds != 20 && nrounds != 12);
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for (i = 0; i < nrounds; i += 2) {
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x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16);
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x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16);
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x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 16);
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x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 16);
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x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 12);
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x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 12);
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x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 12);
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x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 12);
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x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 8);
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x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 8);
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x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 8);
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x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 8);
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x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 7);
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x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 7);
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x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 7);
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x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 7);
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x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 16);
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x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 16);
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x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 16);
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x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 16);
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x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 12);
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x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 12);
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x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 12);
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x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 12);
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x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 8);
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x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 8);
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x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 8);
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x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 8);
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x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 7);
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x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 7);
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x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7);
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x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7);
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}
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}
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/**
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* chacha_block - generate one keystream block and increment block counter
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* @state: input state matrix (16 32-bit words)
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* @stream: output keystream block (64 bytes)
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* @nrounds: number of rounds (20 or 12; 20 is recommended)
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*
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* This is the ChaCha core, a function from 64-byte strings to 64-byte strings.
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* The caller has already converted the endianness of the input. This function
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* also handles incrementing the block counter in the input matrix.
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*/
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void chacha_block_generic(u32 *state, u8 *stream, int nrounds)
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{
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u32 x[16];
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int i;
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memcpy(x, state, 64);
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chacha_permute(x, nrounds);
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for (i = 0; i < ARRAY_SIZE(x); i++)
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put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
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state[12]++;
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}
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EXPORT_SYMBOL(chacha_block_generic);
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/**
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* hchacha_block_generic - abbreviated ChaCha core, for XChaCha
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* @state: input state matrix (16 32-bit words)
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* @out: output (8 32-bit words)
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* @nrounds: number of rounds (20 or 12; 20 is recommended)
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*
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* HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step
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* towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha
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* skips the final addition of the initial state, and outputs only certain words
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* of the state. It should not be used for streaming directly.
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*/
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void hchacha_block_generic(const u32 *state, u32 *stream, int nrounds)
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{
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u32 x[16];
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memcpy(x, state, 64);
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chacha_permute(x, nrounds);
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memcpy(&stream[0], &x[0], 16);
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memcpy(&stream[4], &x[12], 16);
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}
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EXPORT_SYMBOL(hchacha_block_generic);
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