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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/crypto/krb/checksum_confounder.c */
/*
* Copyright (C) 2009 by the Massachusetts Institute of Technology.
* All rights reserved.
*
* Export of this software from the United States of America may
* require a specific license from the United States Government.
* It is the responsibility of any person or organization contemplating
* export to obtain such a license before exporting.
*
* WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
* distribute this software and its documentation for any purpose and
* without fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright notice and
* this permission notice appear in supporting documentation, and that
* the name of M.I.T. not be used in advertising or publicity pertaining
* to distribution of the software without specific, written prior
* permission. Furthermore if you modify this software you must label
* your software as modified software and not distribute it in such a
* fashion that it might be confused with the original M.I.T. software.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is" without express
* or implied warranty.
*/
/*
* Confounder checksum implementation, using tokens of the form:
* enc(xorkey, confounder | hash(confounder | data))
* where xorkey is the key XOR'd with 0xf0 bytes.
*/
#include "crypto_int.h"
/* Derive a key by XOR with 0xF0 bytes. */
static krb5_error_code
mk_xorkey(krb5_key origkey, krb5_key *xorkey)
{
krb5_error_code retval = 0;
unsigned char *xorbytes;
krb5_keyblock xorkeyblock;
size_t i = 0;
xorbytes = malloc(origkey->keyblock.length);
if (xorbytes == NULL)
return ENOMEM;
memcpy(xorbytes, origkey->keyblock.contents, origkey->keyblock.length);
for (i = 0; i < origkey->keyblock.length; i++)
xorbytes[i] ^= 0xf0;
/* Do a shallow copy here. */
xorkeyblock = origkey->keyblock;
xorkeyblock.contents = xorbytes;
retval = krb5_k_create_key(0, &xorkeyblock, xorkey);
zapfree(xorbytes, sizeof(xorbytes));
return retval;
}
krb5_error_code
krb5int_confounder_checksum(const struct krb5_cksumtypes *ctp,
krb5_key key, krb5_keyusage usage,
const krb5_crypto_iov *data, size_t num_data,
krb5_data *output)
{
krb5_error_code ret;
krb5_data conf, hashval;
krb5_key xorkey = NULL;
krb5_crypto_iov *hash_iov, iov;
size_t blocksize = ctp->enc->block_size, hashsize = ctp->hash->hashsize;
/* Partition the output buffer into confounder and hash. */
conf = make_data(output->data, blocksize);
hashval = make_data(output->data + blocksize, hashsize);
/* Create the confounder. */
ret = krb5_c_random_make_octets(NULL, &conf);
if (ret != 0)
return ret;
ret = mk_xorkey(key, &xorkey);
if (ret)
return ret;
/* Hash the confounder, then the input data. */
hash_iov = k5alloc((num_data + 1) * sizeof(krb5_crypto_iov), &ret);
if (hash_iov == NULL)
goto cleanup;
hash_iov[0].flags = KRB5_CRYPTO_TYPE_DATA;
hash_iov[0].data = conf;
memcpy(hash_iov + 1, data, num_data * sizeof(krb5_crypto_iov));
ret = ctp->hash->hash(hash_iov, num_data + 1, &hashval);
if (ret != 0)
goto cleanup;
/* Confounder and hash are in output buffer; encrypt them in place. */
iov.flags = KRB5_CRYPTO_TYPE_DATA;
iov.data = *output;
ret = ctp->enc->encrypt(xorkey, NULL, &iov, 1);
cleanup:
free(hash_iov);
krb5_k_free_key(NULL, xorkey);
return ret;
}
krb5_error_code krb5int_confounder_verify(const struct krb5_cksumtypes *ctp,
krb5_key key, krb5_keyusage usage,
const krb5_crypto_iov *data,
size_t num_data,
const krb5_data *input,
krb5_boolean *valid)
{
krb5_error_code ret;
unsigned char *plaintext = NULL;
krb5_key xorkey = NULL;
krb5_data computed = empty_data();
krb5_crypto_iov *hash_iov = NULL, iov;
size_t blocksize = ctp->enc->block_size, hashsize = ctp->hash->hashsize;
plaintext = k5alloc(input->length, &ret);
if (plaintext == NULL)
return ret;
ret = mk_xorkey(key, &xorkey);
if (ret != 0)
goto cleanup;
/* Decrypt the input checksum. */
iov.flags = KRB5_CRYPTO_TYPE_DATA;
iov.data = make_data(plaintext, input->length);
memcpy(plaintext, input->data, input->length);
ret = ctp->enc->decrypt(xorkey, NULL, &iov, 1);
if (ret != 0)
goto cleanup;
/* Hash the confounder, then the input data. */
hash_iov = k5alloc((num_data + 1) * sizeof(krb5_crypto_iov), &ret);
if (hash_iov == NULL)
goto cleanup;
hash_iov[0].flags = KRB5_CRYPTO_TYPE_DATA;
hash_iov[0].data = make_data(plaintext, blocksize);
memcpy(hash_iov + 1, data, num_data * sizeof(krb5_crypto_iov));
ret = alloc_data(&computed, hashsize);
if (ret != 0)
goto cleanup;
ret = ctp->hash->hash(hash_iov, num_data + 1, &computed);
if (ret != 0)
goto cleanup;
/* Compare the decrypted hash to the computed one. */
*valid = (memcmp(plaintext + blocksize, computed.data, hashsize) == 0);
cleanup:
zapfree(plaintext, input->length);
zapfree(computed.data, hashsize);
free(hash_iov);
krb5_k_free_key(NULL, xorkey);
return ret;
}
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