228 lines
6.9 KiB
Plaintext
228 lines
6.9 KiB
Plaintext
.\" This file is dual-licensed. Choose whichever you want.
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.\"
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.\" The first licence is a regular 2-clause BSD licence. The second licence
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.\" is the CC-0 from Creative Commons. It is intended to release Monocypher
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.\" to the public domain. The BSD licence serves as a fallback option.
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.\"
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.\" SPDX-License-Identifier: BSD-2-Clause OR CC0-1.0
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.\"
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.\" ----------------------------------------------------------------------------
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.\"
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.\" Copyright (c) 2019-2020 Fabio Scotoni
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.\" All rights reserved.
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.\"
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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 are
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.\" met:
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.\"
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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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.\"
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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
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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.\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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.\" HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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.\" OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" ----------------------------------------------------------------------------
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.\"
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.\" Written in 2019-2020 by Fabio Scotoni
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.\"
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.\" To the extent possible under law, the author(s) have dedicated all copyright
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.\" and related neighboring rights to this software to the public domain
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.\" worldwide. This software is distributed without any warranty.
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.\"
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.\" You should have received a copy of the CC0 Public Domain Dedication along
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.\" with this software. If not, see
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.\" <https://creativecommons.org/publicdomain/zero/1.0/>
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.\"
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.Dd March 2, 2020
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.Dt CRYPTO_HMAC_SHA512 3MONOCYPHER
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.Os
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.Sh NAME
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.Nm crypto_hmac_sha512 ,
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.Nm crypto_hmac_sha512_init ,
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.Nm crypto_hmac_sha512_update ,
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.Nm crypto_hmac_sha512_final
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.Nd cryptographic hash-based message authentication code with SHA-512
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.Sh SYNOPSIS
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.In monocypher-ed25519.h
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.Ft void
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.Fo crypto_hmac_sha512
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.Fa "uint8_t hmac[64]"
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.Fa "const uint8_t *key"
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.Fa "size_t key_size"
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.Fa "const uint8_t *message"
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.Fa "size_t message_size"
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.Fc
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.Ft void
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.Fo crypto_hmac_sha512_init
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.Fa "crypto_hmac_sha512_ctx *ctx"
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.Fa "const uint8_t *key"
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.Fa "size_t key_size"
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.Fc
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.Ft void
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.Fo crypto_hmac_sha512_update
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.Fa "crypto_hmac_sha512_ctx *ctx"
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.Fa "const uint8_t *message"
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.Fa "size_t message_size"
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.Fc
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.Ft void
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.Fo crypto_hmac_sha512_final
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.Fa "crypto_hmac_sha512_ctx *ctx"
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.Fa "uint8_t hmac[64]"
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.Fc
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.Sh DESCRIPTION
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HMAC with SHA-512 is a cryptographically secure message authentication
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code (MAC),
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provided to enable compatibility with other cryptographic systems.
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It is generally recommended to use
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.Xr crypto_blake2b_general 3monocypher
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instead,
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as it performs faster on x86_64 CPUs.
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.Pp
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The arguments are:
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.Bl -tag -width Ds
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.It Fa hmac
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The output MAC,
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which is always 64 bytes long.
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.It Fa key
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Some secret key.
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One cannot predict the final hash without it.
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Users may want to wipe the key with
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.Xr crypto_wipe 3monocypher
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once they are done with it.
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.It Fa key_size
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Length of
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.Fa key ,
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in bytes.
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32 is a good default.
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Keys longer than 128 bytes will be reduced to 64 bytes by hashing
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the key with SHA-512.
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.It Fa message
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The message to compute the HMAC for.
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May overlap with
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.Fa hmac .
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May be
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.Dv NULL
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if
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.Fa message_size
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is 0.
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.It Fa message_size
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Length of
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.Fa message ,
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in bytes.
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.El
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.Pp
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An incremental interface is provided.
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It is useful for handling streams of data or
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large files without using too much memory.
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This interface uses three steps:
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.Bl -bullet
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.It
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initialisation with
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.Fn crypto_hmac_sha512_init ,
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which sets up a context with the hashing parameters;
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.It
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update with
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.Fn crypto_hmac_sha512_update ,
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which hashes the message chunk by chunk, and keep the intermediary
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result in the context;
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.It
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and finalisation with
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.Fn crypto_hmac_sha512_final ,
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which produces the final hash.
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The
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.Ft crypto_hmac_sha512_ctx
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is automatically wiped upon finalisation.
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.El
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.Pp
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.Fn crypto_hmac_sha512
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is a convenience function that
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performs
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.Fn crypto_hmac_sha512_init ,
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.Fn crypto_hmac_sha512_update ,
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and
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.Fn crypto_hmac_sha512_final .
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.Pp
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MACs may be truncated safely down to at most 16 bytes;
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the
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.Xr crypto_verify64 3monocypher ,
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.Xr crypto_verify32 3monocypher ,
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and
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.Xr crypto_verify16 3monocypher
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functions can be used to to compare (possibly truncated) MACs.
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.Sh RETURN VALUES
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These functions return nothing.
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.Sh EXAMPLES
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The following examples assume the existence of
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.Fn arc4random_buf ,
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which fills the given buffer with cryptographically secure random bytes.
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If
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.Fn arc4random_buf
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does not exist on your system, see
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.Xr intro 3monocypher
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for advice about how to generate cryptographically secure random bytes.
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.Pp
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Computing a message authentication code all at once:
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.Bd -literal -offset indent
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uint8_t hash [64]; /* Output hash (between 1 and 64 bytes) */
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uint8_t key [32]; /* Key (at least 1 byte) */
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uint8_t message[10] = "Lorem ipsu"; /* Message to authenticate */
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arc4random_buf(key, 32);
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crypto_hmac_sha512(hash, key, 32, message, 500);
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(message, 500);
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crypto_wipe(key, 32);
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.Ed
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.Pp
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Computing a message authentication code incrementally:
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.Bd -literal -offset indent
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uint8_t hash [64]; /* Output hash (between 1 and 64 bytes) */
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uint8_t key [32]; /* Key (at least 1 byte) */
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uint8_t message[500] = {1}; /* Message to authenticate */
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crypto_hmac_sha512_ctx ctx;
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arc4random_buf(key, 32);
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crypto_hmac_sha512_init(&ctx, key, 32);
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/* Wipe the key */
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crypto_wipe(key, 32);
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for (size_t i = 0; i < 500; i += 100) {
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crypto_hmac_sha512_update(&ctx, message + i, 100);
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/* Wipe secrets if they are no longer needed */
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crypto_wipe(message + i, 100);
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}
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crypto_hmac_sha512_final(&ctx, hash);
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.Ed
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.Sh SEE ALSO
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.Xr crypto_blake2b 3monocypher ,
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.Xr crypto_lock 3monocypher ,
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.Xr crypto_poly1305 3monocypher ,
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.Xr crypto_sha512 3monocypher ,
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.Xr intro 3monocypher
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.Sh STANDARDS
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These functions implement HMAC with SHA-512.
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HMAC and SHA-512 itself are described in RFC 6234;
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SHA-512 is also described in the Federal Information Processing Standard
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(FIPS) 180-4;
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HMAC is also described in FIPS 198-1.
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.Sh HISTORY
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The
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.Fn crypto_hmac_sha512 ,
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.Fn crypto_hmac_sha512_init ,
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.Fn crypto_hmac_sha512_update ,
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and
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.Fn crypto_hmac_sha512_final
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functions first appeared in Monocypher 3.0.0.
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