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https://github.com/cryb-to/cryb-to.git
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b28507b0e9
In my eagerness to eliminate a branch which is taken once per 2^38 bytes of keystream, I forgot that the state words are in host order. Thus, the counter increment code worked fine on little-endian machines, but not on big-endian ones. Switch to a simpler (branchful) solution.
202 lines
5.8 KiB
C
202 lines
5.8 KiB
C
/*-
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* Copyright (c) 2017 Dag-Erling Smørgrav
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "cryb/impl.h"
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#include <stdint.h>
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#include <string.h>
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#include <cryb/assert.h>
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#include <cryb/bitwise.h>
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#include <cryb/endian.h>
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#include <cryb/memset_s.h>
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#include <cryb/salsa.h>
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#define SALSA_QR(x, a, b, c, d) \
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do { \
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x[a] ^= rol32(x[d] + x[c], 7); \
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x[b] ^= rol32(x[a] + x[d], 9); \
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x[c] ^= rol32(x[b] + x[a], 13); \
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x[d] ^= rol32(x[c] + x[b], 18); \
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} while (0)
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static const char magic128[] = "expand 16-byte k";
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static const char magic256[] = "expand 32-byte k";
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/*
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* Fill the state array with 16 bytes of magic and 32 bytes of key,
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* repeating the key if necessary. The 8-byte stream position and the
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* 8-byte nonce are initialized to all-zeroes. The number of rounds is
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* set to 20, the most commonly used value.
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*/
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void
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salsa_init(salsa_ctx *ctx, cipher_mode mode CRYB_UNUSED,
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const uint8_t *key, size_t keylen)
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{
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assert(mode == CIPHER_MODE_ENCRYPT || mode == CIPHER_MODE_DECRYPT);
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assert(keylen == 16 || keylen == 32);
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memset(ctx, 0, sizeof *ctx);
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if (keylen == 32) {
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/* magic */
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ctx->state[ 0] = le32dec(magic256 + 0);
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ctx->state[ 5] = le32dec(magic256 + 4);
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ctx->state[10] = le32dec(magic256 + 8);
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ctx->state[15] = le32dec(magic256 + 12);
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/* first half of key */
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ctx->state[ 1] = le32dec(key + 0);
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ctx->state[ 2] = le32dec(key + 4);
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ctx->state[ 3] = le32dec(key + 8);
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ctx->state[ 4] = le32dec(key + 12);
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/* second half of key */
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ctx->state[11] = le32dec(key + 16);
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ctx->state[12] = le32dec(key + 20);
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ctx->state[13] = le32dec(key + 24);
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ctx->state[14] = le32dec(key + 28);
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} else {
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/* magic */
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ctx->state[ 0] = le32dec(magic128 + 0);
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ctx->state[ 5] = le32dec(magic128 + 4);
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ctx->state[10] = le32dec(magic128 + 8);
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ctx->state[15] = le32dec(magic128 + 12);
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/* first half of key */
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ctx->state[ 1] = le32dec(key + 0);
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ctx->state[ 2] = le32dec(key + 4);
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ctx->state[ 3] = le32dec(key + 8);
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ctx->state[ 4] = le32dec(key + 12);
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/* repeat first half of key */
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ctx->state[11] = le32dec(key + 0);
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ctx->state[12] = le32dec(key + 4);
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ctx->state[13] = le32dec(key + 8);
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ctx->state[14] = le32dec(key + 12);
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}
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ctx->rounds = 20;
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}
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/*
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* Reset the stream position, load a new nonce, and change the number of
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* rounds if requested.
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*/
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void
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salsa_reset(salsa_ctx *ctx, const uint8_t *nonce, unsigned int rounds)
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{
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/* reset stream counter */
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ctx->state[8] = 0;
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ctx->state[9] = 0;
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/* copy nonce */
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ctx->state[6] = le32dec(nonce + 0);
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ctx->state[7] = le32dec(nonce + 4);
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/* set rounds if specified */
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if (rounds != 0)
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ctx->rounds = rounds;
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}
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/*
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* Generate a block of keystream.
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*/
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size_t
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salsa_keystream(salsa_ctx *ctx, uint8_t *ks, size_t len)
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{
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return (salsa_encrypt(ctx, NULL, ks, len));
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}
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/*
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* Encryption: generate a block of keystream, xor it with the plaintext to
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* produce the ciphertext, and increment the stream position.
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*/
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size_t
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salsa_encrypt(salsa_ctx *ctx, const void *vpt, uint8_t *ct, size_t len)
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{
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const uint8_t *pt = vpt;
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uint32_t mix[16];
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uint8_t ks[64];
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unsigned int b, i;
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len -= len % sizeof ks;
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for (b = 0; b < len; b += sizeof ks) {
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memcpy(mix, ctx->state, sizeof mix);
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for (i = 0; i < ctx->rounds; i += 2) {
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SALSA_QR(mix, 4, 8, 12, 0);
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SALSA_QR(mix, 9, 13, 1, 5);
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SALSA_QR(mix, 14, 2, 6, 10);
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SALSA_QR(mix, 3, 7, 11, 15);
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SALSA_QR(mix, 1, 2, 3, 0);
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SALSA_QR(mix, 6, 7, 4, 5);
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SALSA_QR(mix, 11, 8, 9, 10);
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SALSA_QR(mix, 12, 13, 14, 15);
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}
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for (i = 0; i < 16; ++i)
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le32enc(ks + i * 4, ctx->state[i] + mix[i]);
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if (pt == NULL) {
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memcpy(ct, ks, sizeof ks);
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ct += sizeof ks;
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} else {
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for (i = 0; i < 64 && i < len; ++i)
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*ct++ = *pt++ ^ ks[i];
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}
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if (++ctx->state[12] == 0)
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++ctx->state[13];
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}
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return (len);
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}
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/*
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* Decryption: identical to encryption.
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*/
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size_t
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salsa_decrypt(salsa_ctx *ctx, const uint8_t *ct, void *vpt, size_t len)
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{
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return (salsa_encrypt(ctx, ct, vpt, len));
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}
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/*
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* Wipe our state.
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*/
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void
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salsa_finish(salsa_ctx *ctx)
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{
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(void)memset_s(ctx, 0, sizeof *ctx, sizeof *ctx);
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}
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cipher_algorithm salsa_cipher = {
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.name = "salsa",
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.contextlen = sizeof(salsa_ctx),
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.blocklen = 64,
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.keylen = 32,
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.init = (cipher_init_func)salsa_init,
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.keystream = (cipher_keystream_func)salsa_keystream,
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.encrypt = (cipher_encrypt_func)salsa_encrypt,
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.decrypt = (cipher_decrypt_func)salsa_decrypt,
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.finish = (cipher_finish_func)salsa_finish,
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};
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