hmac.c   [plain text]

/*
 * Copyright (C) 1998 by the FundsXpress, INC.
 * 
 * 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 FundsXpress. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  FundsXpress makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include "k5-int.h"

/*
 * the HMAC transform looks like:
 *
 * H(K XOR opad, H(K XOR ipad, text))
 *
 * where H is a cryptographic hash
 * K is an n byte key
 * ipad is the byte 0x36 repeated blocksize times
 * opad is the byte 0x5c repeated blocksize times
 * and text is the data being protected
 */

krb5_error_code
krb5_hmac(const struct krb5_hash_provider *hash, const krb5_keyblock *key,
	  unsigned int icount, const krb5_data *input, krb5_data *output)
{
    size_t hashsize, blocksize;
    unsigned char *xorkey, *ihash;
    int i;
    krb5_data *hashin, hashout;
    krb5_error_code ret;

    hashsize = hash->hashsize;
    blocksize = hash->blocksize;

    if (key->length > blocksize)
	return(KRB5_CRYPTO_INTERNAL);
    if (output->length < hashsize)
	return(KRB5_BAD_MSIZE);
    /* if this isn't > 0, then there won't be enough space in this
       array to compute the outer hash */
    if (icount == 0)
	return(KRB5_CRYPTO_INTERNAL);

    /* allocate space for the xor key, hash input vector, and inner hash */

    if ((xorkey = (unsigned char *) malloc(blocksize)) == NULL)
	return(ENOMEM);
    if ((ihash = (unsigned char *) malloc(hashsize)) == NULL) {
	free(xorkey);
	return(ENOMEM);
    }
    if ((hashin = (krb5_data *)malloc(sizeof(krb5_data)*(icount+1))) == NULL) {
	free(ihash);
	free(xorkey);
	return(ENOMEM);
    }

    /* create the inner padded key */

    memset(xorkey, 0x36, blocksize);

    for (i=0; i<key->length; i++)
	xorkey[i] ^= key->contents[i];

    /* compute the inner hash */

    for (i=0; i<icount; i++) {
	hashin[0].length = blocksize;
	hashin[0].data = (char *) xorkey;
	hashin[i+1] = input[i];
    }

    hashout.length = hashsize;
    hashout.data = (char *) ihash;

    if ((ret = ((*(hash->hash))(icount+1, hashin, &hashout))))
	goto cleanup;

    /* create the outer padded key */

    memset(xorkey, 0x5c, blocksize);

    for (i=0; i<key->length; i++)
	xorkey[i] ^= key->contents[i];

    /* compute the outer hash */

    hashin[0].length = blocksize;
    hashin[0].data = (char *) xorkey;
    hashin[1] = hashout;

    output->length = hashsize;

    if ((ret = ((*(hash->hash))(2, hashin, output))))
	memset(output->data, 0, output->length);

    /* ret is set correctly by the prior call */

cleanup:
    memset(xorkey, 0, blocksize);
    memset(ihash, 0, hashsize);

    free(hashin);
    free(ihash);
    free(xorkey);

    return(ret);
}