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Currently when timing the pbkdf algorithm a fixed key size of 32 bytes is used. This results in inaccurate timings for certain hashes depending on their digest size. For example when using sha1 with aes-256, this causes us to measure time for the master key digest doing 2 sha1 operations per iteration, instead of 1. Instead we should pass in the desired key size to the timing routine that matches the key size that will be used for real later. Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
157 lines
4.9 KiB
C
157 lines
4.9 KiB
C
/*
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* QEMU Crypto PBKDF support (Password-Based Key Derivation Function)
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*
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* Copyright (c) 2015-2016 Red Hat, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#ifndef QCRYPTO_PBKDF_H
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#define QCRYPTO_PBKDF_H
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#include "crypto/hash.h"
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/**
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* This module provides an interface to the PBKDF2 algorithm
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*
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* https://en.wikipedia.org/wiki/PBKDF2
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*
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* <example>
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* <title>Generating an AES encryption key from a user password</title>
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* <programlisting>
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* #include "crypto/cipher.h"
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* #include "crypto/random.h"
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* #include "crypto/pbkdf.h"
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*
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* ....
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*
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* char *password = "a-typical-awful-user-password";
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* size_t nkey = qcrypto_cipher_get_key_len(QCRYPTO_CIPHER_ALG_AES_128);
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* uint8_t *salt = g_new0(uint8_t, nkey);
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* uint8_t *key = g_new0(uint8_t, nkey);
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* int iterations;
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* QCryptoCipher *cipher;
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*
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* if (qcrypto_random_bytes(salt, nkey, errp) < 0) {
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* g_free(key);
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* g_free(salt);
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* return -1;
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* }
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*
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* iterations = qcrypto_pbkdf2_count_iters(QCRYPTO_HASH_ALG_SHA256,
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* (const uint8_t *)password,
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* strlen(password),
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* salt, nkey, errp);
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* if (iterations < 0) {
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* g_free(key);
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* g_free(salt);
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* return -1;
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* }
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*
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* if (qcrypto_pbkdf2(QCRYPTO_HASH_ALG_SHA256,
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* (const uint8_t *)password, strlen(password),
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* salt, nkey, iterations, key, nkey, errp) < 0) {
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* g_free(key);
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* g_free(salt);
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* return -1;
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* }
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*
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* g_free(salt);
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*
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* cipher = qcrypto_cipher_new(QCRYPTO_CIPHER_ALG_AES_128,
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* QCRYPTO_CIPHER_MODE_ECB,
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* key, nkey, errp);
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* g_free(key);
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*
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* ....encrypt some data...
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*
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* qcrypto_cipher_free(cipher);
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* </programlisting>
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* </example>
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*
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*/
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/**
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* qcrypto_pbkdf2_supports:
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* @hash: the hash algorithm
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*
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* Determine if the current build supports the PBKDF2 algorithm
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* in combination with the hash @hash.
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*
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* Returns true if supported, false otherwise
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*/
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bool qcrypto_pbkdf2_supports(QCryptoHashAlgorithm hash);
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/**
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* qcrypto_pbkdf2:
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* @hash: the hash algorithm to use
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* @key: the user password / key
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* @nkey: the length of @key in bytes
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* @salt: a random salt
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* @nsalt: length of @salt in bytes
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* @iterations: the number of iterations to compute
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* @out: pointer to pre-allocated buffer to hold output
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* @nout: length of @out in bytes
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* @errp: pointer to a NULL-initialized error object
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*
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* Apply the PBKDF2 algorithm to derive an encryption
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* key from a user password provided in @key. The
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* @salt parameter is used to perturb the algorithm.
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* The @iterations count determines how many times
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* the hashing process is run, which influences how
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* hard it is to crack the key. The number of @iterations
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* should be large enough such that the algorithm takes
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* 1 second or longer to derive a key. The derived key
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* will be stored in the preallocated buffer @out.
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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_pbkdf2(QCryptoHashAlgorithm hash,
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const uint8_t *key, size_t nkey,
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const uint8_t *salt, size_t nsalt,
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uint64_t iterations,
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uint8_t *out, size_t nout,
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Error **errp);
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/**
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* qcrypto_pbkdf2_count_iters:
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* @hash: the hash algorithm to use
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* @key: the user password / key
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* @nkey: the length of @key in bytes
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* @salt: a random salt
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* @nsalt: length of @salt in bytes
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* @nout: size of desired derived key
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* @errp: pointer to a NULL-initialized error object
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*
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* Time the PBKDF2 algorithm to determine how many
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* iterations are required to derive an encryption
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* key from a user password provided in @key in 1
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* second of compute time. The result of this can
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* be used as a the @iterations parameter of a later
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* call to qcrypto_pbkdf2(). The value of @nout should
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* match that value that will later be provided with
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* a call to qcrypto_pbkdf2().
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*
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* Returns: number of iterations in 1 second, -1 on error
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*/
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uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
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const uint8_t *key, size_t nkey,
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const uint8_t *salt, size_t nsalt,
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size_t nout,
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Error **errp);
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#endif /* QCRYPTO_PBKDF_H */
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