135 lines
4.3 KiB
C
135 lines
4.3 KiB
C
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/*
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* QEMU Crypto anti forensic information splitter
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*
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* Copyright (c) 2015-2016 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef QCRYPTO_AFSPLIT_H
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#define QCRYPTO_AFSPLIT_H
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#include "crypto/hash.h"
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/**
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* This module implements the anti-forensic splitter that is specified
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* as part of the LUKS format:
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*
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* http://clemens.endorphin.org/cryptography
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* http://clemens.endorphin.org/TKS1-draft.pdf
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*
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* The core idea is to take a short piece of data (key material)
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* and process it to expand it to a much larger piece of data.
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* The expansion process is reversible, to obtain the original
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* short data. The key property of the expansion is that if any
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* byte in the larger data set is changed / missing, it should be
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* impossible to recreate the original short data.
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*
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* <example>
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* <title>Creating a large split key for storage</title>
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* <programlisting>
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* size_t nkey = 32;
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* uint32_t stripes = 32768; // To produce a 1 MB split key
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* uint8_t *masterkey = ....a 32-byte AES key...
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* uint8_t *splitkey;
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*
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* splitkey = g_new0(uint8_t, nkey * stripes);
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*
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* if (qcrypto_afsplit_encode(QCRYPTO_HASH_ALG_SHA256,
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* nkey, stripes,
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* masterkey, splitkey, errp) < 0) {
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* g_free(splitkey);
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* g_free(masterkey);
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* return -1;
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* }
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*
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* ...store splitkey somewhere...
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*
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* g_free(splitkey);
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* g_free(masterkey);
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* </programlisting>
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* </example>
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*
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* <example>
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* <title>Retrieving a master key from storage</title>
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* <programlisting>
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* size_t nkey = 32;
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* uint32_t stripes = 32768; // To produce a 1 MB split key
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* uint8_t *masterkey;
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* uint8_t *splitkey = .... read in 1 MB of data...
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*
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* masterkey = g_new0(uint8_t, nkey);
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*
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* if (qcrypto_afsplit_decode(QCRYPTO_HASH_ALG_SHA256,
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* nkey, stripes,
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* splitkey, masterkey, errp) < 0) {
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* g_free(splitkey);
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* g_free(masterkey);
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* return -1;
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* }
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*
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* ..decrypt data with masterkey...
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*
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* g_free(splitkey);
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* g_free(masterkey);
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* </programlisting>
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* </example>
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*/
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/**
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* qcrypto_afsplit_encode:
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* @hash: the hash algorithm to use for data expansion
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* @blocklen: the size of @in in bytes
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* @stripes: the number of times to expand @in in size
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* @in: the master key to be expanded in size
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* @out: preallocated buffer to hold the split key
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* @errp: pointer to a NULL-initialized error object
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*
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* Split the data in @in, which is @blocklen bytes in
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* size, to form a larger piece of data @out, which is
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* @blocklen * @stripes bytes in size.
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*
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* Returns: 0 on success, -1 on error;
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*/
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int qcrypto_afsplit_encode(QCryptoHashAlgorithm hash,
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size_t blocklen,
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uint32_t stripes,
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const uint8_t *in,
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uint8_t *out,
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Error **errp);
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/**
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* qcrypto_afsplit_decode:
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* @hash: the hash algorithm to use for data compression
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* @blocklen: the size of @out in bytes
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* @stripes: the number of times to decrease @in in size
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* @in: the split key to be recombined
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* @out: preallocated buffer to hold the master key
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* @errp: pointer to a NULL-initialized error object
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*
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* Join the data in @in, which is @blocklen * @stripes
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* bytes in size, to form the original small piece of
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* data @out, which is @blocklen bytes in size.
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*
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* Returns: 0 on success, -1 on error;
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*/
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int qcrypto_afsplit_decode(QCryptoHashAlgorithm hash,
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size_t blocklen,
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uint32_t stripes,
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const uint8_t *in,
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uint8_t *out,
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Error **errp);
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#endif /* QCRYPTO_AFSPLIT_H */
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