/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/crypto/krb/checksum_dk_cmac.c */
/*
 * Copyright 2010 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.
 */

#include "crypto_int.h"

#define K5CLENGTH 5 /* 32 bit net byte order integer + one byte seed */

krb5_error_code
krb5int_dk_cmac_checksum(const struct krb5_cksumtypes *ctp,
                         krb5_key key, krb5_keyusage usage,
                         const krb5_crypto_iov *data, size_t num_data,
                         krb5_data *output)
{
    const struct krb5_enc_provider *enc = ctp->enc;
    krb5_error_code ret;
    unsigned char constantdata[K5CLENGTH];
    krb5_data datain;
    krb5_key kc;

    /* Derive the key. */
    datain = make_data(constantdata, K5CLENGTH);
    store_32_be(usage, constantdata);
    constantdata[4] = (char) 0x99;
    ret = krb5int_derive_key(enc, NULL, key, &kc, &datain,
                             DERIVE_SP800_108_CMAC);
    if (ret != 0)
        return ret;

    /* Hash the data. */
    ret = krb5int_cmac_checksum(enc, kc, data, num_data, output);
    if (ret != 0)
        memset(output->data, 0, output->length);

    krb5_k_free_key(NULL, kc);
    return ret;
}