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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* plugins/preauth/spake/util.c - Utility functions for SPAKE preauth module */
/*
* Copyright (C) 2015 by the Massachusetts Institute of Technology.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "k5-int.h"
#include "trace.h"
#include "util.h"
#include "groups.h"
/* Use data to construct a single-element pa-data list of type
* KRB5_PADATA_SPAKE. Claim data's memory on success or failure. */
krb5_error_code
convert_to_padata(krb5_data *data, krb5_pa_data ***pa_out)
{
krb5_pa_data *pa = NULL, **list = NULL;
list = calloc(2, sizeof(*list));
if (list == NULL)
goto fail;
pa = calloc(1, sizeof(*pa));
if (pa == NULL)
goto fail;
pa->magic = KV5M_PA_DATA;
pa->pa_type = KRB5_PADATA_SPAKE;
pa->length = data->length;
pa->contents = (uint8_t *)data->data;
list[0] = pa;
list[1] = NULL;
*pa_out = list;
free(data);
return 0;
fail:
free(list);
free(pa);
free(data->data);
free(data);
return ENOMEM;
}
/*
* Update the transcript hash thash with its current value and the
* concatenation of data1 and data2, using the hash function for group. Either
* data1 or data2 may be NULL to omit it. Allocate thash if it is empty.
*/
krb5_error_code
update_thash(krb5_context context, groupstate *gstate, int32_t group,
krb5_data *thash, const krb5_data *data1, const krb5_data *data2)
{
krb5_error_code ret;
size_t hashlen;
krb5_data dlist[3];
const krb5_data empty = empty_data();
if (thash->length == 0) {
/* Initialize the transcript hash to all zeros. */
ret = group_hash_len(group, &hashlen);
if (ret)
return ret;
ret = alloc_data(thash, hashlen);
if (ret)
return ret;
}
/* Set up the data array and hash it with the group's hash function. */
dlist[0] = *thash;
dlist[1] = (data1 != NULL) ? *data1 : empty;
dlist[2] = (data2 != NULL) ? *data2 : empty;
return group_hash(context, gstate, group, dlist, 3,
(uint8_t *)thash->data);
}
/* Derive a byte vector for the SPAKE w multiplier input from ikey. Place
* result in allocated storage in *wbytes_out. */
krb5_error_code
derive_wbytes(krb5_context context, int32_t group, const krb5_keyblock *ikey,
krb5_data *wbytes_out)
{
krb5_error_code ret;
const char prefix[] = "SPAKEsecret";
size_t mult_len, prefix_len = sizeof(prefix) - 1;
krb5_data prf_input = empty_data(), wbytes = empty_data();
*wbytes_out = empty_data();
/* Allocate space for a multiplier. */
ret = group_mult_len(group, &mult_len);
if (ret)
goto cleanup;
ret = alloc_data(&wbytes, mult_len);
if (ret)
goto cleanup;
/* Compose the PRF input string. */
ret = alloc_data(&prf_input, prefix_len + 4);
if (ret)
goto cleanup;
memcpy(prf_input.data, prefix, prefix_len);
store_32_be(group, prf_input.data + prefix_len);
/* Derive the SPAKE input from the initial reply key with PRF+. */
ret = krb5_c_prfplus(context, ikey, &prf_input, &wbytes);
if (ret)
goto cleanup;
*wbytes_out = wbytes;
wbytes = empty_data();
cleanup:
free(prf_input.data);
zapfree(wbytes.data, wbytes.length);
return ret;
}
/*
* Derive K'[n] from the group number, the initial key enctype, the initial
* multiplier, the SPAKE result, the transcript hash, and the encoded
* KDC-REQ-BODY. Place the result in allocated storage in *out.
*/
krb5_error_code
derive_key(krb5_context context, groupstate *gstate, int32_t group,
const krb5_keyblock *ikey, const krb5_data *wbytes,
const krb5_data *spakeresult, const krb5_data *thash,
const krb5_data *der_req, uint32_t n, krb5_keyblock **out)
{
krb5_error_code ret;
krb5_data dlist[9], seed = empty_data(), d;
uint8_t groupnbuf[4], etypenbuf[4], nbuf[4], bcount;
size_t hashlen, seedlen, keylen, nblocks, i;
size_t ndata = sizeof(dlist) / sizeof(*dlist);
krb5_keyblock *hkey = NULL;
*out = NULL;
store_32_be(group, groupnbuf);
store_32_be(n, nbuf);
store_32_be(ikey->enctype, etypenbuf);
dlist[0] = string2data("SPAKEkey");
dlist[1] = make_data(groupnbuf, sizeof(groupnbuf));
dlist[2] = make_data(etypenbuf, sizeof(etypenbuf));
dlist[3] = *wbytes;
dlist[4] = *spakeresult;
dlist[5] = *thash;
dlist[6] = *der_req;
dlist[7] = make_data(nbuf, sizeof(nbuf));
dlist[8] = make_data(&bcount, 1);
/* Count the number of hash blocks required (should be 1 for all current
* scenarios) and allocate space. */
ret = group_hash_len(group, &hashlen);
if (ret)
goto cleanup;
ret = krb5_c_keylengths(context, ikey->enctype, &seedlen, &keylen);
if (ret)
goto cleanup;
nblocks = (seedlen + hashlen - 1) / hashlen;
ret = alloc_data(&seed, nblocks * hashlen);
if (ret)
goto cleanup;
/* Compute and concatenate hash blocks to fill the seed buffer. */
for (i = 0; i < nblocks; i++) {
bcount = i + 1;
ret = group_hash(context, gstate, group, dlist, ndata,
(uint8_t *)seed.data + i * hashlen);
if (ret)
goto cleanup;
}
ret = krb5_init_keyblock(context, ikey->enctype, keylen, &hkey);
if (ret)
goto cleanup;
d = make_data(seed.data, seedlen);
ret = krb5_c_random_to_key(context, ikey->enctype, &d, hkey);
if (ret)
goto cleanup;
ret = krb5_c_fx_cf2_simple(context, ikey, "SPAKE", hkey, "keyderiv", out);
cleanup:
zapfree(seed.data, seed.length);
krb5_free_keyblock(context, hkey);
return ret;
}
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