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NetBSD/sbin/cgdconfig/hkdf_hmac_sha256.h

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cgdconfig(8): Add support for shared keys. New clause `shared <id> algorithm <alg> subkey <info>' in a keygen block enables `cgdconfig -C' to reuse a key between different params files, so you can, e.g., use a single password for multiple disks. This is better than simply caching the password itself because: - Hashing the password is expensive, so it should only be done once. Suppose your budget is time t before you get bored, and you calibrate password hash parameters to unlock n disks before you get bored waiting for `cgdconfig -C'. . With n password hashings the adversary's cost goes up only by a factor of t/n. . With one password hashing and n subkeys the adversary's cost goes up by a factor of n. And if you ever add a disk, rehashing it will make `cgdconfig -C' go over budget, whereas another subkey adds negligible cost to you. - Subkeys work for other types of keygen blocks, like shell_cmd, which could be used to get a key from a hardware token that needs a button press. The <info> parameter must be different for each params file; everything else in the keygen block must be the same. With this clause, the keygen block determines a shared key used only to derive keys; the actual key used by cgdconfig is derived from the shared key by the specified algorithm. The only supported algorithm is hkdf-hmac-sha256, which uses HKDF-Expand of RFC 5869 instantiated with SHA-256. Example: algorithm aes-cbc; iv-method encblkno1; keylength 128; verify_method none; keygen pkcs5_pbkdf2/sha1 { iterations 39361; salt AAAAgMoHiYonye6KogdYJAobCHE=; shared "pw" algorithm hkdf-hmac-sha256 subkey AAAAgFlw0BMQ5gY+haYkZ6JC+yY=; }; The key used for this disk will be derived by HKDF-HMAC-SHA256_k(WXDQExDmBj6FpiRnokL7Jg==), where k is the outcome of PBKDF2-SHA1 with the given parameters. Note that <info> encodes a four-byte prefix giving the big-endian length in bits of the info argument to HKDF, just like all other bit strings in cgdconfig parameters files. If you have multiple disks configured using the same keygen block except for the info parameter, `cgdconfig -C' will only prompt once for your passphrase, generate a shared key k with PBKDF2 as usual, and then reuse it for each of the disks.
2022-08-12 13:49:17 +03:00
/* $NetBSD: hkdf_hmac_sha256.h,v 1.1 2022/08/12 10:49:17 riastradh Exp $ */
/*-
* Copyright (c) 2022 The NetBSD Foundation, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef HKDF_HMAC_SHA256_H
#define HKDF_HMAC_SHA256_H
#include <stddef.h>
int hkdf_hmac_sha256(void *, size_t,
const void *, size_t,
const void *, size_t);
int hkdf_hmac_sha256_selftest(void);
#endif /* HKDF_HMAC_SHA256_H */