/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* lib/crypto/krb/enc_etm.c - encrypt-then-mac construction for aes-sha2 */
/*
* 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 "crypto_int.h"
unsigned int
krb5int_aes2_crypto_length(const struct krb5_keytypes *ktp,
krb5_cryptotype type)
{
switch (type) {
case KRB5_CRYPTO_TYPE_HEADER:
return ktp->enc->block_size;
case KRB5_CRYPTO_TYPE_PADDING:
return 0;
case KRB5_CRYPTO_TYPE_TRAILER:
case KRB5_CRYPTO_TYPE_CHECKSUM:
return ktp->hash->hashsize / 2;
default:
assert(0 && "invalid cryptotype passed to krb5int_aes2_crypto_length");
return 0;
}
}
/* Derive encryption and integrity keys for CMAC-using enctypes. */
static krb5_error_code
derive_keys(const struct krb5_keytypes *ktp, krb5_key key,
krb5_keyusage usage, krb5_key *ke_out, krb5_data *ki_out)
{
krb5_error_code ret;
uint8_t label[5];
krb5_data label_data = make_data(label, 5), ki = empty_data();
krb5_key ke = NULL;
*ke_out = NULL;
*ki_out = empty_data();
/* Derive the encryption key. */
store_32_be(usage, label);
label[4] = 0xAA;
ret = krb5int_derive_key(ktp->enc, ktp->hash, key, &ke, &label_data,
DERIVE_SP800_108_HMAC);
if (ret)
goto cleanup;
/* Derive the integrity key. */
label[4] = 0x55;
ret = alloc_data(&ki, ktp->hash->hashsize / 2);
if (ret)
goto cleanup;
ret = krb5int_derive_random(NULL, ktp->hash, key, &ki, &label_data,
DERIVE_SP800_108_HMAC);
if (ret)
goto cleanup;
*ke_out = ke;
ke = NULL;
*ki_out = ki;
ki = empty_data();
cleanup:
krb5_k_free_key(NULL, ke);
zapfree(ki.data, ki.length);
return ret;
}
/* Compute an HMAC checksum over the cipher state and data. Allocate enough
* space in *out for the checksum. */
static krb5_error_code
hmac_ivec_data(const struct krb5_keytypes *ktp, const krb5_data *ki,
const krb5_data *ivec, krb5_crypto_iov *data, size_t num_data,
krb5_data *out)
{
krb5_error_code ret;
krb5_data zeroivec = empty_data();
krb5_crypto_iov *iovs = NULL;
krb5_keyblock kb = { 0 };
if (ivec == NULL) {
ret = ktp->enc->init_state(NULL, 0, &zeroivec);
if (ret)
goto cleanup;
ivec = &zeroivec;
}
/* Make a copy of data with an extra iov at the beginning for the ivec. */
iovs = k5calloc(num_data + 1, sizeof(*iovs), &ret);
if (iovs == NULL)
goto cleanup;
iovs[0].flags = KRB5_CRYPTO_TYPE_DATA;
iovs[0].data = *ivec;
memcpy(iovs + 1, data, num_data * sizeof(*iovs));
ret = alloc_data(out, ktp->hash->hashsize);
if (ret)
goto cleanup;
kb.length = ki->length;
kb.contents = (uint8_t *)ki->data;
ret = krb5int_hmac_keyblock(ktp->hash, &kb, iovs, num_data + 1, out);
cleanup:
if (zeroivec.data != NULL)
ktp->enc->free_state(&zeroivec);
free(iovs);
return ret;
}
krb5_error_code
krb5int_etm_encrypt(const struct krb5_keytypes *ktp, krb5_key key,
krb5_keyusage usage, const krb5_data *ivec,
krb5_crypto_iov *data, size_t num_data)
{
const struct krb5_enc_provider *enc = ktp->enc;
krb5_error_code ret;
krb5_data ivcopy = empty_data(), cksum = empty_data();
krb5_crypto_iov *header, *trailer, *padding;
krb5_key ke = NULL;
krb5_data ki = empty_data();
unsigned int trailer_len;
/* E(Confounder | Plaintext) | Checksum(IV | ciphertext) */
trailer_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_TRAILER);
/* Validate header and trailer lengths, and zero out padding length. */
header = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_HEADER);
if (header == NULL || header->data.length < enc->block_size)
return KRB5_BAD_MSIZE;
trailer = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_TRAILER);
if (trailer == NULL || trailer->data.length < trailer_len)
return KRB5_BAD_MSIZE;
padding = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_PADDING);
if (padding != NULL)
padding->data.length = 0;
if (ivec != NULL) {
ret = alloc_data(&ivcopy, ivec->length);
if (ret)
goto cleanup;
memcpy(ivcopy.data, ivec->data, ivec->length);
}
/* Derive the encryption and integrity keys. */
ret = derive_keys(ktp, key, usage, &ke, &ki);
if (ret)
goto cleanup;
/* Generate confounder. */
header->data.length = enc->block_size;
ret = krb5_c_random_make_octets(NULL, &header->data);
if (ret)
goto cleanup;
/* Encrypt the plaintext (header | data). */
ret = enc->encrypt(ke, (ivec == NULL) ? NULL : &ivcopy, data, num_data);
if (ret)
goto cleanup;
/* HMAC the IV, confounder, and ciphertext with sign-only data. */
ret = hmac_ivec_data(ktp, &ki, ivec, data, num_data, &cksum);
if (ret)
goto cleanup;
/* Truncate the HMAC checksum to the trailer length. */
assert(trailer_len <= cksum.length);
memcpy(trailer->data.data, cksum.data, trailer_len);
trailer->data.length = trailer_len;
/* Copy out the updated ivec if desired. */
if (ivec != NULL)
memcpy(ivec->data, ivcopy.data, ivcopy.length);
cleanup:
krb5_k_free_key(NULL, ke);
zapfree(ki.data, ki.length);
free(cksum.data);
zapfree(ivcopy.data, ivcopy.length);
return ret;
}
krb5_error_code
krb5int_etm_decrypt(const struct krb5_keytypes *ktp, krb5_key key,
krb5_keyusage usage, const krb5_data *ivec,
krb5_crypto_iov *data, size_t num_data)
{
const struct krb5_enc_provider *enc = ktp->enc;
krb5_error_code ret;
krb5_data cksum = empty_data();
krb5_crypto_iov *header, *trailer;
krb5_key ke = NULL;
krb5_data ki = empty_data();
unsigned int trailer_len;
trailer_len = ktp->crypto_length(ktp, KRB5_CRYPTO_TYPE_TRAILER);
/* Validate header and trailer lengths. */
header = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_HEADER);
if (header == NULL || header->data.length != enc->block_size)
return KRB5_BAD_MSIZE;
trailer = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_TRAILER);
if (trailer == NULL || trailer->data.length != trailer_len)
return KRB5_BAD_MSIZE;
/* Derive the encryption and integrity keys. */
ret = derive_keys(ktp, key, usage, &ke, &ki);
if (ret)
goto cleanup;
/* HMAC the IV, confounder, and ciphertext with sign-only data. */
ret = hmac_ivec_data(ktp, &ki, ivec, data, num_data, &cksum);
if (ret)
goto cleanup;
/* Compare only the possibly truncated length. */
assert(trailer_len <= cksum.length);
if (k5_bcmp(cksum.data, trailer->data.data, trailer_len) != 0) {
ret = KRB5KRB_AP_ERR_BAD_INTEGRITY;
goto cleanup;
}
/* Decrypt the ciphertext (header | data | padding). */
ret = enc->decrypt(ke, ivec, data, num_data);
cleanup:
krb5_k_free_key(NULL, ke);
zapfree(ki.data, ki.length);
zapfree(cksum.data, cksum.length);
return ret;
}