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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/crypto/krb/cf2.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.
*/
/*
* Implement KRB_FX_CF2 function per draft-ietf-krb-wg-preauth-framework-09.
* Take two keys and two pepper strings as input and return a combined key.
*/
#include "crypto_int.h"
/*
* Call the PRF function multiple times with the pepper prefixed with
* a count byte to get enough bits of output.
*/
static krb5_error_code
prf_plus(krb5_context context, krb5_keyblock *k, const char *pepper,
size_t keybytes, char **out)
{
krb5_error_code retval = 0;
size_t prflen, iterations;
krb5_data out_data;
krb5_data in_data;
char *buffer = NULL;
struct k5buf prf_inbuf;
krb5int_buf_init_dynamic(&prf_inbuf);
krb5int_buf_add_len(&prf_inbuf, "\001", 1);
krb5int_buf_add(&prf_inbuf, pepper);
retval = krb5_c_prf_length( context, k->enctype, &prflen);
if (retval)
goto cleanup;
iterations = keybytes / prflen;
if (keybytes % prflen != 0)
iterations++;
assert(iterations <= 254);
buffer = k5alloc(iterations * prflen, &retval);
if (retval)
goto cleanup;
if (krb5int_buf_len(&prf_inbuf) == -1) {
retval = ENOMEM;
goto cleanup;
}
in_data.length = (krb5_int32) krb5int_buf_len(&prf_inbuf);
in_data.data = krb5int_buf_data(&prf_inbuf);
out_data.length = prflen;
out_data.data = buffer;
while (iterations > 0) {
retval = krb5_c_prf(context, k, &in_data, &out_data);
if (retval)
goto cleanup;
out_data.data += prflen;
in_data.data[0]++;
iterations--;
}
*out = buffer;
buffer = NULL;
cleanup:
free(buffer);
krb5int_free_buf(&prf_inbuf);
return retval;
}
krb5_error_code KRB5_CALLCONV
krb5_c_fx_cf2_simple(krb5_context context,
krb5_keyblock *k1, const char *pepper1,
krb5_keyblock *k2, const char *pepper2,
krb5_keyblock **out)
{
const struct krb5_keytypes *out_enctype;
size_t keybytes, keylength, i;
char *prf1 = NULL, *prf2 = NULL;
krb5_data keydata;
krb5_enctype out_enctype_num;
krb5_error_code retval = 0;
krb5_keyblock *out_key = NULL;
if (k1 == NULL || !krb5_c_valid_enctype(k1->enctype))
return KRB5_BAD_ENCTYPE;
if (k2 == NULL || !krb5_c_valid_enctype(k2->enctype))
return KRB5_BAD_ENCTYPE;
out_enctype_num = k1->enctype;
assert(out != NULL);
out_enctype = find_enctype(out_enctype_num);
assert(out_enctype != NULL);
if (out_enctype->prf == NULL) {
if (context)
krb5int_set_error(&(context->err), KRB5_CRYPTO_INTERNAL,
_("Enctype %d has no PRF"), out_enctype_num);
return KRB5_CRYPTO_INTERNAL;
}
keybytes = out_enctype->enc->keybytes;
keylength = out_enctype->enc->keylength;
retval = prf_plus(context, k1, pepper1, keybytes, &prf1);
if (retval)
goto cleanup;
retval = prf_plus(context, k2, pepper2, keybytes, &prf2);
if (retval)
goto cleanup;
for (i = 0; i < keybytes; i++)
prf1[i] ^= prf2[i];
retval = krb5int_c_init_keyblock(context, out_enctype_num, keylength,
&out_key);
if (retval)
goto cleanup;
keydata.data = prf1;
keydata.length = keybytes;
retval = (*out_enctype->rand2key)(&keydata, out_key);
if (retval)
goto cleanup;
*out = out_key;
out_key = NULL;
cleanup:
krb5int_c_free_keyblock( context, out_key);
zapfree(prf1, keybytes);
zapfree(prf2, keybytes);
return retval;
}
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