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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/crypto/krb/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.
*/
/*
* Portions Copyright (C) The Internet Society (2006).
*
* This document is subject to the rights, licenses and restrictions
* contained in BCP 78, and except as set forth therein, the authors
* retain all their rights.
*
* This document and the information contained herein are provided on an
* "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
* OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
* ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
* INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
* INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
* WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
*/
#include "crypto_int.h"
#define BLOCK_SIZE 16
static unsigned char const_Rb[BLOCK_SIZE] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x87
};
static void
xor_128(unsigned char *a, unsigned char *b, unsigned char *out)
{
int z;
for (z = 0; z < BLOCK_SIZE / 4; z++) {
unsigned char *aptr = &a[z * 4];
unsigned char *bptr = &b[z * 4];
unsigned char *outptr = &out[z * 4];
store_32_n(load_32_n(aptr) ^ load_32_n(bptr), outptr);
}
}
static void
leftshift_onebit(unsigned char *input, unsigned char *output)
{
int i;
unsigned char overflow = 0;
for (i = BLOCK_SIZE - 1; i >= 0; i--) {
output[i] = input[i] << 1;
output[i] |= overflow;
overflow = (input[i] & 0x80) ? 1 : 0;
}
}
/* Generate subkeys K1 and K2 as described in RFC 4493 figure 2.2. */
static krb5_error_code
generate_subkey(const struct krb5_enc_provider *enc,
krb5_key key,
unsigned char *K1,
unsigned char *K2)
{
unsigned char L[BLOCK_SIZE];
unsigned char tmp[BLOCK_SIZE];
krb5_data d;
krb5_error_code ret;
/* L := encrypt(K, const_Zero) */
memset(L, 0, sizeof(L));
d = make_data(L, BLOCK_SIZE);
ret = encrypt_block(enc, key, &d);
if (ret != 0)
return ret;
/* K1 := (MSB(L) == 0) ? L << 1 : (L << 1) XOR const_Rb */
if ((L[0] & 0x80) == 0) {
leftshift_onebit(L, K1);
} else {
leftshift_onebit(L, tmp);
xor_128(tmp, const_Rb, K1);
}
/* K2 := (MSB(K1) == 0) ? K1 << 1 : (K1 << 1) XOR const_Rb */
if ((K1[0] & 0x80) == 0) {
leftshift_onebit(K1, K2);
} else {
leftshift_onebit(K1, tmp);
xor_128(tmp, const_Rb, K2);
}
return 0;
}
/* Pad out lastb with a 1 bit followed by 0 bits, placing the result in pad. */
static void
padding(unsigned char *lastb, unsigned char *pad, int length)
{
int j;
/* original last block */
for (j = 0; j < BLOCK_SIZE; j++) {
if (j < length) {
pad[j] = lastb[j];
} else if (j == length) {
pad[j] = 0x80;
} else {
pad[j] = 0x00;
}
}
}
/*
* Implementation of CMAC algorithm. When used with AES, this function
* is compatible with RFC 4493 figure 2.3.
*/
krb5_error_code
krb5int_cmac_checksum(const struct krb5_enc_provider *enc, krb5_key key,
const krb5_crypto_iov *data, size_t num_data,
krb5_data *output)
{
unsigned char Y[BLOCK_SIZE], M_last[BLOCK_SIZE], padded[BLOCK_SIZE];
unsigned char K1[BLOCK_SIZE], K2[BLOCK_SIZE];
unsigned char input[BLOCK_SIZE];
unsigned int n, i, flag;
krb5_error_code ret;
struct iov_block_state iov_state;
unsigned int length;
krb5_crypto_iov iov[1];
krb5_data d;
assert(enc->cbc_mac != NULL);
if (enc->block_size != BLOCK_SIZE)
return KRB5_BAD_MSIZE;
for (i = 0, length = 0; i < num_data; i++) {
const krb5_crypto_iov *piov = &data[i];
if (SIGN_IOV(piov))
length += piov->data.length;
}
/* Step 1. */
ret = generate_subkey(enc, key, K1, K2);
if (ret != 0)
return ret;
/* Step 2. */
n = (length + BLOCK_SIZE - 1) / BLOCK_SIZE;
/* Step 3. */
if (n == 0) {
n = 1;
flag = 0;
} else {
flag = ((length % BLOCK_SIZE) == 0);
}
iov[0].flags = KRB5_CRYPTO_TYPE_DATA;
iov[0].data = make_data(input, BLOCK_SIZE);
/* Step 5 (we'll do step 4 in a bit). */
memset(Y, 0, BLOCK_SIZE);
d = make_data(Y, BLOCK_SIZE);
/* Step 6 (all but last block). */
IOV_BLOCK_STATE_INIT(&iov_state);
iov_state.include_sign_only = 1;
for (i = 0; i < n - 1; i++) {
krb5int_c_iov_get_block(input, BLOCK_SIZE, data, num_data, &iov_state);
ret = enc->cbc_mac(key, iov, 1, &d, &d);
if (ret != 0)
return ret;
}
/* Step 4. */
krb5int_c_iov_get_block(input, BLOCK_SIZE, data, num_data, &iov_state);
if (flag) {
/* last block is complete block */
xor_128(input, K1, M_last);
} else {
padding(input, padded, length % BLOCK_SIZE);
xor_128(padded, K2, M_last);
}
/* Step 6 (last block). */
iov[0].data = make_data(M_last, BLOCK_SIZE);
ret = enc->cbc_mac(key, iov, 1, &d, &d);
if (ret != 0)
return ret;
assert(output->length >= d.length);
output->length = d.length;
memcpy(output->data, d.data, d.length);
return 0;
}
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