/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */

/* lib/crypto/krb/enc_dk_cmac.c - Derived-key enctype functions using CMAC */

/*

 * Copyright 2008, 2009, 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.

 */

#include "crypto_int.h"

#define K5CLENGTH 5 /* 32 bit net byte order integer + one byte seed */

/* AEAD */

unsigned int

krb5int_camellia_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->enc->block_size;

    default:

        assert(0 && "bad type passed to krb5int_camellia_crypto_length");

        return 0;

    }

}

/* Derive encryption and integrity keys for CMAC-using enctypes. */

static krb5_error_code

derive_keys(const struct krb5_enc_provider *enc, krb5_key key,

            krb5_keyusage usage, krb5_key *ke_out, krb5_key *ki_out)

{

    krb5_error_code ret;

    unsigned char buf[K5CLENGTH];

    krb5_data constant = make_data(buf, K5CLENGTH);

    krb5_key ke, ki;

    *ke_out = *ki_out = NULL;

    /* Derive the encryption key. */

    store_32_be(usage, buf);

    buf[4] = 0xAA;

    ret = krb5int_derive_key(enc, NULL, key, &ke, &constant,

                             DERIVE_SP800_108_CMAC);

    if (ret != 0)

        return ret;

    /* Derive the integrity key. */

    buf[4] = 0x55;

    ret = krb5int_derive_key(enc, NULL, key, &ki, &constant,

                             DERIVE_SP800_108_CMAC);

    if (ret != 0) {

        krb5_k_free_key(NULL, ke);

        return ret;

    }

    *ke_out = ke;

    *ki_out = ki;

    return 0;

}

krb5_error_code

krb5int_dk_cmac_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_crypto_iov *header, *trailer, *padding;

    krb5_key ke = NULL, ki = NULL;

    /* E(Confounder | Plaintext | Pad) | Checksum */

    /* 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 < enc->block_size)

        return KRB5_BAD_MSIZE;

    padding = krb5int_c_locate_iov(data, num_data, KRB5_CRYPTO_TYPE_PADDING);

    if (padding != NULL)

        padding->data.length = 0;

    /* Derive the encryption and integrity keys. */

    ret = derive_keys(enc, key, usage, &ke, &ki;;

    if (ret != 0)

        goto cleanup;

    /* Generate confounder. */

    header->data.length = enc->block_size;

    ret = krb5_c_random_make_octets(NULL, &header->data);

    if (ret != 0)

        goto cleanup;

    /* Checksum the plaintext. */

    ret = krb5int_cmac_checksum(enc, ki, data, num_data, &trailer->data);

    if (ret != 0)

        goto cleanup;

    /* Encrypt the plaintext (header | data | padding) */

    ret = enc->encrypt(ke, ivec, data, num_data);

    if (ret != 0)

        goto cleanup;

cleanup:

    krb5_k_free_key(NULL, ke);

    krb5_k_free_key(NULL, ki);

    return ret;

}

krb5_error_code

krb5int_dk_cmac_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_crypto_iov *header, *trailer;

    krb5_data cksum = empty_data();

    krb5_key ke = NULL, ki = NULL;

    /* E(Confounder | Plaintext | Pad) | Checksum */

    /* 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 != enc->block_size)

        return KRB5_BAD_MSIZE;

    /* Derive the encryption and integrity keys. */

    ret = derive_keys(enc, key, usage, &ke, &ki;;

    if (ret != 0)

        goto cleanup;

    /* Decrypt the plaintext (header | data | padding). */

    ret = enc->decrypt(ke, ivec, data, num_data);

    if (ret != 0)

        goto cleanup;

    /* Verify the hash. */

    ret = alloc_data(&cksum, enc->block_size);

    if (ret != 0)

        goto cleanup;

    ret = krb5int_cmac_checksum(enc, ki, data, num_data, &cksum);

    if (ret != 0)

        goto cleanup;

    if (k5_bcmp(cksum.data, trailer->data.data, enc->block_size) != 0)

        ret = KRB5KRB_AP_ERR_BAD_INTEGRITY;

cleanup:

    krb5_k_free_key(NULL, ke);

    krb5_k_free_key(NULL, ki);

    zapfree(cksum.data, cksum.length);

    return ret;

}