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Diffstat (limited to 'lib/chacha.c')
| -rw-r--r-- | lib/chacha.c | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/lib/chacha.c b/lib/chacha.c new file mode 100644 index 000000000000..a46d2832dbab --- /dev/null +++ b/lib/chacha.c @@ -0,0 +1,117 @@ +/* + * The "hash function" used as the core of the ChaCha stream cipher (RFC7539) + * + * Copyright (C) 2015 Martin Willi + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + */ + +#include <linux/kernel.h> +#include <linux/export.h> +#include <linux/bitops.h> +#include <linux/cryptohash.h> +#include <asm/unaligned.h> +#include <crypto/chacha.h> + +static void chacha_permute(u32 *x, int nrounds) +{ + int i; + + /* whitelist the allowed round counts */ + WARN_ON_ONCE(nrounds != 20 && nrounds != 12); + + for (i = 0; i < nrounds; i += 2) { + x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16); + x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16); + x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 16); + x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 16); + + x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 12); + x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 12); + x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 12); + x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 12); + + x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 8); + x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 8); + x[2] += x[6]; x[14] = rol32(x[14] ^ x[2], 8); + x[3] += x[7]; x[15] = rol32(x[15] ^ x[3], 8); + + x[8] += x[12]; x[4] = rol32(x[4] ^ x[8], 7); + x[9] += x[13]; x[5] = rol32(x[5] ^ x[9], 7); + x[10] += x[14]; x[6] = rol32(x[6] ^ x[10], 7); + x[11] += x[15]; x[7] = rol32(x[7] ^ x[11], 7); + + x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 16); + x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 16); + x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 16); + x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 16); + + x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 12); + x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 12); + x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 12); + x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 12); + + x[0] += x[5]; x[15] = rol32(x[15] ^ x[0], 8); + x[1] += x[6]; x[12] = rol32(x[12] ^ x[1], 8); + x[2] += x[7]; x[13] = rol32(x[13] ^ x[2], 8); + x[3] += x[4]; x[14] = rol32(x[14] ^ x[3], 8); + + x[10] += x[15]; x[5] = rol32(x[5] ^ x[10], 7); + x[11] += x[12]; x[6] = rol32(x[6] ^ x[11], 7); + x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7); + x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7); + } +} + +/** + * chacha_block - generate one keystream block and increment block counter + * @state: input state matrix (16 32-bit words) + * @stream: output keystream block (64 bytes) + * @nrounds: number of rounds (20 or 12; 20 is recommended) + * + * This is the ChaCha core, a function from 64-byte strings to 64-byte strings. + * The caller has already converted the endianness of the input. This function + * also handles incrementing the block counter in the input matrix. + */ +void chacha_block(u32 *state, u8 *stream, int nrounds) +{ + u32 x[16]; + int i; + + memcpy(x, state, 64); + + chacha_permute(x, nrounds); + + for (i = 0; i < ARRAY_SIZE(x); i++) + put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]); + + state[12]++; +} +EXPORT_SYMBOL(chacha_block); + +/** + * hchacha_block - abbreviated ChaCha core, for XChaCha + * @in: input state matrix (16 32-bit words) + * @out: output (8 32-bit words) + * @nrounds: number of rounds (20 or 12; 20 is recommended) + * + * HChaCha is the ChaCha equivalent of HSalsa and is an intermediate step + * towards XChaCha (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha + * skips the final addition of the initial state, and outputs only certain words + * of the state. It should not be used for streaming directly. + */ +void hchacha_block(const u32 *in, u32 *out, int nrounds) +{ + u32 x[16]; + + memcpy(x, in, 64); + + chacha_permute(x, nrounds); + + memcpy(&out[0], &x[0], 16); + memcpy(&out[4], &x[12], 16); +} +EXPORT_SYMBOL(hchacha_block); |