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crypto: add support for anti-forensic split algorithm

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The LUKS format specifies an anti-forensic split algorithm which
is used to artificially expand the size of the key material on
disk. This is an implementation of that algorithm.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrange 2015-10-23 16:14:25 +01:00
parent cb730894ae
commit 5a95e0fccd
6 changed files with 490 additions and 0 deletions
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135
include/crypto/afsplit.h Normal file
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/*
* QEMU Crypto anti forensic information splitter
*
* Copyright (c) 2015-2016 Red Hat, Inc.
*
* This library 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.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#ifndef QCRYPTO_AFSPLIT_H__
#define QCRYPTO_AFSPLIT_H__
#include "crypto/hash.h"
/**
* This module implements the anti-forensic splitter that is specified
* as part of the LUKS format:
*
* http://clemens.endorphin.org/cryptography
* http://clemens.endorphin.org/TKS1-draft.pdf
*
* The core idea is to take a short piece of data (key material)
* and process it to expand it to a much larger piece of data.
* The expansion process is reversible, to obtain the original
* short data. The key property of the expansion is that if any
* byte in the larger data set is changed / missing, it should be
* impossible to recreate the original short data.
*
* <example>
* <title>Creating a large split key for storage</title>
* <programlisting>
* size_t nkey = 32;
* uint32_t stripes = 32768; // To produce a 1 MB split key
* uint8_t *masterkey = ....a 32-byte AES key...
* uint8_t *splitkey;
*
* splitkey = g_new0(uint8_t, nkey * stripes);
*
* if (qcrypto_afsplit_encode(QCRYPTO_HASH_ALG_SHA256,
* nkey, stripes,
* masterkey, splitkey, errp) < 0) {
* g_free(splitkey);
* g_free(masterkey);
* return -1;
* }
*
* ...store splitkey somewhere...
*
* g_free(splitkey);
* g_free(masterkey);
* </programlisting>
* </example>
*
* <example>
* <title>Retrieving a master key from storage</title>
* <programlisting>
* size_t nkey = 32;
* uint32_t stripes = 32768; // To produce a 1 MB split key
* uint8_t *masterkey;
* uint8_t *splitkey = .... read in 1 MB of data...
*
* masterkey = g_new0(uint8_t, nkey);
*
* if (qcrypto_afsplit_decode(QCRYPTO_HASH_ALG_SHA256,
* nkey, stripes,
* splitkey, masterkey, errp) < 0) {
* g_free(splitkey);
* g_free(masterkey);
* return -1;
* }
*
* ..decrypt data with masterkey...
*
* g_free(splitkey);
* g_free(masterkey);
* </programlisting>
* </example>
*/
/**
* qcrypto_afsplit_encode:
* @hash: the hash algorithm to use for data expansion
* @blocklen: the size of @in in bytes
* @stripes: the number of times to expand @in in size
* @in: the master key to be expanded in size
* @out: preallocated buffer to hold the split key
* @errp: pointer to a NULL-initialized error object
*
* Split the data in @in, which is @blocklen bytes in
* size, to form a larger piece of data @out, which is
* @blocklen * @stripes bytes in size.
*
* Returns: 0 on success, -1 on error;
*/
int qcrypto_afsplit_encode(QCryptoHashAlgorithm hash,
size_t blocklen,
uint32_t stripes,
const uint8_t *in,
uint8_t *out,
Error **errp);
/**
* qcrypto_afsplit_decode:
* @hash: the hash algorithm to use for data compression
* @blocklen: the size of @out in bytes
* @stripes: the number of times to decrease @in in size
* @in: the split key to be recombined
* @out: preallocated buffer to hold the master key
* @errp: pointer to a NULL-initialized error object
*
* Join the data in @in, which is @blocklen * @stripes
* bytes in size, to form the original small piece of
* data @out, which is @blocklen bytes in size.
*
* Returns: 0 on success, -1 on error;
*/
int qcrypto_afsplit_decode(QCryptoHashAlgorithm hash,
size_t blocklen,
uint32_t stripes,
const uint8_t *in,
uint8_t *out,
Error **errp);
#endif /* QCRYPTO_AFSPLIT_H__ */