/* $NetBSD: rxkad_kdf.c,v 1.4 2023/06/19 21:41:44 christos Exp $ */
/*
* Copyright (c) 1995-2003 Kungliga Tekniska Högskolan
* (Royal Institute of Technology, Stockholm, Sweden).
* All rights reserved.
*
* Portions Copyright (c) 2013-2014 Carnegie Mellon University
* All rights reserved.
*
* Portions Copyright (c) 2013 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:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. 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.
*
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE 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 INSTITUTE 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.
*/
#define HC_DEPRECATED_CRYPTO
#include "kafs_locl.h"
static int rxkad_derive_des_key(const void *, size_t, char[8]);
static int compress_parity_bits(void *, size_t *);
/**
* Use NIST SP800-108 with HMAC(MD5) in counter mode as the PRF to derive a
* des key from another type of key.
*
* L is 64, as we take 64 random bits and turn them into a 56-bit des key.
* The output of hmac_md5 is 128 bits; we take the first 64 only, so n
* properly should be 1. However, we apply a slight variation due to the
* possibility of producing a weak des key. If the output key is weak, do NOT
* simply correct it, instead, the counter is advanced and the next output
* used. As such, we code so as to have n be the full 255 permitted by our
* encoding of the counter i in an 8-bit field. L itself is encoded as a
* 32-bit field, big-endian. We use the constant string "rxkad" as a label
* for this key derivation, the standard NUL byte separator, and omit a
* key-derivation context. The input key is unique to the krb5 service ticket,
* which is unlikely to be used in an other location. If it is used in such
* a fashion, both locations will derive the same des key from the PRF, but
* this is no different from if a krb5 des key had been used in the same way,
* as traditional krb5 rxkad uses the ticket session key directly as the token
* key.
*
* @param[in] in pointer to input key data
* @param[in] insize length of input key data
* @param[out] out 8-byte buffer to hold the derived key
*
* @return Returns 0 to indicate success, or an error code.
*
* @retval KRB5DES_WEAK_KEY Successive derivation attempts with all
* 255 possible counter values each produced weak DES keys. This input
* cannot be used to produce a usable key.
*/
static int
rxkad_derive_des_key(const void *in, size_t insize, char out[8])
{
unsigned char i;
static unsigned char label[] = "rxkad";
/* bits of output, as 32 bit word, MSB first */
static unsigned char Lbuf[4] = { 0, 0, 0, 64 };
/* only needs to be 16 for md5, but lets be sure it fits */
unsigned char tmp[64];
unsigned int mdsize;
DES_cblock ktmp;
HMAC_CTX *mctx;
/* stop when 8 bit counter wraps to 0 */
for (i = 1; i; i++) {
#if OPENSSL_VERSION_NUMBER < 0x10100000UL
HMAC_CTX mctxs;
mctx = &mctxs;
HMAC_CTX_init(mctx);
#else
mctx = HMAC_CTX_new();
#endif
HMAC_Init_ex(mctx, in, insize, EVP_md5(), NULL);
HMAC_Update(mctx, &i, 1);
HMAC_Update(mctx, label, sizeof(label)); /* includes label and separator */
HMAC_Update(mctx, Lbuf, 4);
mdsize = sizeof(tmp);
HMAC_Final(mctx, tmp, &mdsize);
memcpy(ktmp, tmp, 8);
#if OPENSSL_VERSION_NUMBER < 0x10100000UL
HMAC_CTX_cleanup(mctx);
#else
HMAC_CTX_free(mctx);
#endif
DES_set_odd_parity(&ktmp);
if (!DES_is_weak_key(&ktmp)) {
memcpy(out, ktmp, 8);
return 0;
}
}
return KRB5DES_WEAK_KEY;
}
/**
* This is the inverse of the random-to-key for 3des specified in
* rfc3961, converting blocks of 8 bytes to blocks of 7 bytes by distributing
* the bits of each 8th byte as the lsb of the previous 7 bytes.
*
* @param[in,out] buffer Buffer containing the key to be converted
* @param[in,out] bufsiz Points to the size of the key data. On
* return, this is updated to reflect the size of the compressed data.
*
* @return Returns 0 to indicate success, or an error code.
*
* @retval KRB5_BAD_KEYSIZE The key size was not a multiple of 8 bytes.
*/
static int
compress_parity_bits(void *buffer, size_t *bufsiz)
{
unsigned char *cb, tmp;
int i, j, nk;
if (*bufsiz % 8 != 0)
return KRB5_BAD_KEYSIZE;
cb = (unsigned char *)buffer;
nk = *bufsiz / 8;
for (i = 0; i < nk; i++) {
tmp = cb[8 * i + 7] >> 1;
for (j = 0; j < 7; j++) {
cb[8 * i + j] &= 0xfe;
cb[8 * i + j] |= tmp & 0x1;
tmp >>= 1;
}
}
for (i = 1; i < nk; i++)
memmove(cb + 7 * i, cb + 8 * i, 7);
*bufsiz = 7 * nk;
return 0;
}
/**
* Derive a DES key for use with rxkad and fcrypt from a given Kerberos
* key of (almost) any type. This function encodes enctype-specific
* knowledge about how to derive a DES key from a given key type.
* If given a des key, use it directly; otherwise, perform any parity
* fixup that may be needed and pass through to the hmad-md5 bits.
*
* @param[in] enctype Kerberos enctype of the input key
* @param[in] keydata Input key data
* @param[in] keylen Size of input key data
* @param[out] output 8-byte buffer to hold the derived key
*
* @return Returns 0 to indicate success, or an error code.
*
* @retval KRB5_PROG_ETYPE_NOSUPP The enctype is one for which rxkad-kdf
* is not supported. This includes several reserved enctypes, enctype
* values used in PKINIT to stand for CMS algorithm identifiers, and all
* private-use (negative) enctypes.
*
* @retval KRB5_BAD_KEYSIZE The key size was not a multiple of 8 bytes
* (for 3DES key types), exactly 8 bytes (for DES key types), or at least
* 8 bytes (for other key types).
*
* @retval KRB5DES_WEAK_KEY Successive derivation attempts with all
* 255 possible counter values each produced weak DES keys. This input
* cannot be used to produce a usable key.
*/
int
_kafs_derive_des_key(krb5_enctype enctype, void *keydata, size_t keylen,
char output[8])
{
int ret = 0;
switch ((int)enctype) {
case ETYPE_DES_CBC_CRC:
case ETYPE_DES_CBC_MD4:
case ETYPE_DES_CBC_MD5:
if (keylen != 8)
return KRB5_BAD_KEYSIZE;
/* Extract session key */
memcpy(output, keydata, 8);
break;
case ETYPE_NULL:
case 4:
case 6:
case 8:
case 9:
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
return KRB5_PROG_ETYPE_NOSUPP;
/*In order to become a "Cryptographic Key" as specified in
* SP800-108, it must be indistinguishable from a random bitstring. */
case ETYPE_DES3_CBC_MD5:
case ETYPE_OLD_DES3_CBC_SHA1:
case ETYPE_DES3_CBC_SHA1:
ret = compress_parity_bits(keydata, &keylen);
if (ret)
return ret;
/* FALLTHROUGH */
default:
if (enctype < 0)
return KRB5_PROG_ETYPE_NOSUPP;
if (keylen < 7)
return KRB5_BAD_KEYSIZE;
ret = rxkad_derive_des_key(keydata, keylen, output);
}
return ret;
}