298 lines
7.1 KiB
C
298 lines
7.1 KiB
C
/*
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* Copyright (C) 2008 Martin Willi
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* Hochschule fuer Technik Rapperswil
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General xcbc License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General xcbc License
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* for more details.
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*/
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#include <string.h>
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#include "xcbc.h"
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#include <debug.h>
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typedef struct private_xcbc_t private_xcbc_t;
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/**
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* Private data of a xcbc_t object.
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*
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* The variable names are the same as in the RFC.
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*/
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struct private_xcbc_t {
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/**
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* Public xcbc_t interface.
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*/
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xcbc_t xcbc;
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/**
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* Block size, in bytes
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*/
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u_int8_t b;
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/**
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* crypter using k1
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*/
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crypter_t *k1;
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/**
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* k2
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*/
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u_int8_t *k2;
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/**
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* k3
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*/
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u_int8_t *k3;
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/**
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* E
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*/
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u_int8_t *e;
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/**
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* remaining, unprocessed bytes in append mode
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*/
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u_int8_t *remaining;
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/**
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* number of bytes in remaining
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*/
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int remaining_bytes;
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/**
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* TRUE if we have zero bytes to xcbc in final()
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*/
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bool zero;
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};
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/**
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* xcbc supplied data, but do not run final operation
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*/
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static void update(private_xcbc_t *this, chunk_t data)
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{
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chunk_t iv;
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if (data.len)
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{
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this->zero = FALSE;
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}
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if (this->remaining_bytes + data.len <= this->b)
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{ /* no complete block, just copy into remaining */
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memcpy(this->remaining + this->remaining_bytes, data.ptr, data.len);
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this->remaining_bytes += data.len;
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return;
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}
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iv = chunk_alloca(this->b);
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memset(iv.ptr, 0, iv.len);
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/* (3) For each block M[i], where i = 1 ... n-1:
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* XOR M[i] with E[i-1], then encrypt the result with Key K1,
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* yielding E[i].
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*/
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/* append data to remaining bytes, process block M[1] */
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memcpy(this->remaining + this->remaining_bytes, data.ptr,
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this->b - this->remaining_bytes);
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data = chunk_skip(data, this->b - this->remaining_bytes);
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memxor(this->e, this->remaining, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->e, this->b), iv, NULL);
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/* process blocks M[2] ... M[n-1] */
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while (data.len > this->b)
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{
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memcpy(this->remaining, data.ptr, this->b);
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data = chunk_skip(data, this->b);
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memxor(this->e, this->remaining, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->e, this->b), iv, NULL);
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}
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/* store remaining bytes of block M[n] */
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memcpy(this->remaining, data.ptr, data.len);
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this->remaining_bytes = data.len;
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}
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/**
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* run last round, data is in this->e
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*/
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static void final(private_xcbc_t *this, u_int8_t *out)
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{
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chunk_t iv;
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iv = chunk_alloca(this->b);
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memset(iv.ptr, 0, iv.len);
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/* (4) For block M[n]: */
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if (this->remaining_bytes == this->b && !this->zero)
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{
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/* a) If the blocksize of M[n] is 128 bits:
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* XOR M[n] with E[n-1] and Key K2, then encrypt the result with
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* Key K1, yielding E[n].
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*/
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memxor(this->e, this->remaining, this->b);
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memxor(this->e, this->k2, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->e, this->b), iv, NULL);
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}
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else
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{
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/* b) If the blocksize of M[n] is less than 128 bits:
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*
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* i) Pad M[n] with a single "1" bit, followed by the number of
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* "0" bits (possibly none) required to increase M[n]'s
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* blocksize to 128 bits.
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*/
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if (this->remaining_bytes < this->b)
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{
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this->remaining[this->remaining_bytes] = 0x80;
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while (++this->remaining_bytes < this->b)
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{
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this->remaining[this->remaining_bytes] = 0x00;
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}
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}
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/* ii) XOR M[n] with E[n-1] and Key K3, then encrypt the result
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* with Key K1, yielding E[n].
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*/
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memxor(this->e, this->remaining, this->b);
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memxor(this->e, this->k3, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->e, this->b), iv, NULL);
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}
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memcpy(out, this->e, this->b);
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/* (2) Define E[0] = 0x00000000000000000000000000000000 */
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memset(this->e, 0, this->b);
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this->remaining_bytes = 0;
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this->zero = TRUE;
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}
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/**
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* Implementation of xcbc_t.get_mac.
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*/
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static void get_mac(private_xcbc_t *this, chunk_t data, u_int8_t *out)
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{
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/* update E, do not process last block */
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update(this, data);
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if (out)
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{ /* if not in append mode, process last block and output result */
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final(this, out);
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}
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}
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/**
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* Implementation of xcbc_t.get_block_size.
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*/
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static size_t get_block_size(private_xcbc_t *this)
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{
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return this->b;
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}
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/**
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* Implementation of xcbc_t.set_key.
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*/
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static void set_key(private_xcbc_t *this, chunk_t key)
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{
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chunk_t iv, k1, lengthened;
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/* we support variable keys from RFC4434 */
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if (key.len == this->b)
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{
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lengthened = key;
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}
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else if (key.len < this->b)
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{ /* pad short keys */
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lengthened = chunk_alloca(this->b);
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memset(lengthened.ptr, 0, lengthened.len);
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memcpy(lengthened.ptr, key.ptr, key.len);
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}
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else
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{ /* shorten key using xcbc */
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lengthened = chunk_alloca(this->b);
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memset(lengthened.ptr, 0, lengthened.len);
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set_key(this, lengthened);
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get_mac(this, key, lengthened.ptr);
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}
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k1 = chunk_alloca(this->b);
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iv = chunk_alloca(this->b);
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memset(iv.ptr, 0, iv.len);
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/*
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* (1) Derive 3 128-bit keys (K1, K2 and K3) from the 128-bit secret
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* key K, as follows:
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* K1 = 0x01010101010101010101010101010101 encrypted with Key K
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* K2 = 0x02020202020202020202020202020202 encrypted with Key K
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* K3 = 0x03030303030303030303030303030303 encrypted with Key K
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*/
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this->k1->set_key(this->k1, lengthened);
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memset(this->k2, 0x02, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->k2, this->b), iv, NULL);
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memset(this->k3, 0x03, this->b);
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this->k1->encrypt(this->k1, chunk_create(this->k3, this->b), iv, NULL);
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memset(k1.ptr, 0x01, this->b);
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this->k1->encrypt(this->k1, k1, iv, NULL);
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this->k1->set_key(this->k1, k1);
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}
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/**
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* Implementation of xcbc_t.destroy.
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*/
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static void destroy(private_xcbc_t *this)
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{
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this->k1->destroy(this->k1);
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free(this->k2);
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free(this->k3);
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free(this->e);
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free(this->remaining);
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free(this);
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}
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/*
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* Described in header
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*/
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xcbc_t *xcbc_create(encryption_algorithm_t algo, size_t key_size)
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{
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private_xcbc_t *this;
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crypter_t *crypter;
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crypter = lib->crypto->create_crypter(lib->crypto, algo, key_size);
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if (!crypter)
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{
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return NULL;
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}
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/* input and output of crypter must be equal for xcbc */
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if (crypter->get_block_size(crypter) != key_size)
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{
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crypter->destroy(crypter);
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return NULL;
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}
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this = malloc_thing(private_xcbc_t);
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this->xcbc.get_mac = (void (*)(xcbc_t *,chunk_t,u_int8_t*))get_mac;
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this->xcbc.get_block_size = (size_t (*)(xcbc_t *))get_block_size;
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this->xcbc.set_key = (void (*)(xcbc_t *,chunk_t))set_key;
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this->xcbc.destroy = (void (*)(xcbc_t *))destroy;
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this->b = crypter->get_block_size(crypter);
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this->k1 = crypter;
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this->k2 = malloc(this->b);
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this->k3 = malloc(this->b);
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this->e = malloc(this->b);
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memset(this->e, 0, this->b);
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this->remaining = malloc(this->b);
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this->remaining_bytes = 0;
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this->zero = TRUE;
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return &this->xcbc;
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}
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