/* $OpenBSD: cts128.c,v 1.6 2022/11/26 16:08:53 tb Exp $ */
/* ====================================================================
 * Copyright (c) 2008 The OpenSSL Project. All rights reserved.
 *
 * Rights for redistribution and usage in source and binary
 * forms are granted according to the OpenSSL license.
 */

#include <openssl/crypto.h>
#include "modes_local.h"
#include <string.h>

#ifndef MODES_DEBUG
# ifndef NDEBUG
#  define NDEBUG
# endif
#endif

/*
 * Trouble with Ciphertext Stealing, CTS, mode is that there is no
 * common official specification, but couple of cipher/application
 * specific ones: RFC2040 and RFC3962. Then there is 'Proposal to
 * Extend CBC Mode By "Ciphertext Stealing"' at NIST site, which
 * deviates from mentioned RFCs. Most notably it allows input to be
 * of block length and it doesn't flip the order of the last two
 * blocks. CTS is being discussed even in ECB context, but it's not
 * adopted for any known application. This implementation provides
 * two interfaces: one compliant with above mentioned RFCs and one
 * compliant with the NIST proposal, both extending CBC mode.
 */

size_t CRYPTO_cts128_encrypt_block(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], block128_f block)
{	size_t residue, n;

	if (len <= 16) return 0;

	if ((residue=len%16) == 0) residue = 16;

	len -= residue;

	CRYPTO_cbc128_encrypt(in,out,len,key,ivec,block);

	in  += len;
	out += len;

	for (n=0; n<residue; ++n)
		ivec[n] ^= in[n];
	(*block)(ivec,ivec,key);
	memcpy(out,out-16,residue);
	memcpy(out-16,ivec,16); 

	return len+residue;
}

size_t CRYPTO_nistcts128_encrypt_block(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], block128_f block)
{	size_t residue, n;

	if (len < 16) return 0;

	residue=len%16;

	len -= residue;

	CRYPTO_cbc128_encrypt(in,out,len,key,ivec,block);

	if (residue==0)	return len;

	in  += len;
	out += len;

	for (n=0; n<residue; ++n)
		ivec[n] ^= in[n];
	(*block)(ivec,ivec,key);
	memcpy(out-16+residue,ivec,16);

	return len+residue;
}

size_t CRYPTO_cts128_encrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], cbc128_f cbc)
{	size_t residue;
	union { size_t align; unsigned char c[16]; } tmp;

	if (len <= 16) return 0;

	if ((residue=len%16) == 0) residue = 16;

	len -= residue;

	(*cbc)(in,out,len,key,ivec,1);

	in  += len;
	out += len;

	memset(tmp.c,0,sizeof(tmp));
	memcpy(tmp.c,in,residue);
	memcpy(out,out-16,residue);
	(*cbc)(tmp.c,out-16,16,key,ivec,1);
	return len+residue;
}

size_t CRYPTO_nistcts128_encrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], cbc128_f cbc)
{	size_t residue;
	union { size_t align; unsigned char c[16]; } tmp;

	if (len < 16) return 0;

	residue=len%16;

	len -= residue;

	(*cbc)(in,out,len,key,ivec,1);

	if (residue==0) return len;

	in  += len;
	out += len;

	memset(tmp.c,0,sizeof(tmp));
	memcpy(tmp.c,in,residue);
	(*cbc)(tmp.c,out-16+residue,16,key,ivec,1);
	return len+residue;
}

size_t CRYPTO_cts128_decrypt_block(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], block128_f block)
{	size_t residue, n;
	union { size_t align; unsigned char c[32]; } tmp;

	if (len<=16) return 0;

	if ((residue=len%16) == 0) residue = 16;

	len -= 16+residue;

	if (len) {
		CRYPTO_cbc128_decrypt(in,out,len,key,ivec,block);
		in  += len;
		out += len;
	}

	(*block)(in,tmp.c+16,key);

	memcpy(tmp.c,tmp.c+16,16);
	memcpy(tmp.c,in+16,residue);
	(*block)(tmp.c,tmp.c,key);

	for(n=0; n<16; ++n) {
		unsigned char c = in[n];
		out[n] = tmp.c[n] ^ ivec[n];
		ivec[n] = c;
	}
	for(residue+=16; n<residue; ++n)
		out[n] = tmp.c[n] ^ in[n];

	return 16+len+residue;
}

size_t CRYPTO_nistcts128_decrypt_block(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], block128_f block)
{	size_t residue, n;
	union { size_t align; unsigned char c[32]; } tmp;

	if (len<16) return 0;

	residue=len%16;

	if (residue==0) {
		CRYPTO_cbc128_decrypt(in,out,len,key,ivec,block);
		return len;
	}

	len -= 16+residue;

	if (len) {
		CRYPTO_cbc128_decrypt(in,out,len,key,ivec,block);
		in  += len;
		out += len;
	}

	(*block)(in+residue,tmp.c+16,key);

	memcpy(tmp.c,tmp.c+16,16);
	memcpy(tmp.c,in,residue);
	(*block)(tmp.c,tmp.c,key);

	for(n=0; n<16; ++n) {
		unsigned char c = in[n];
		out[n] = tmp.c[n] ^ ivec[n];
		ivec[n] = in[n+residue];
		tmp.c[n] = c;
	}
	for(residue+=16; n<residue; ++n)
		out[n] = tmp.c[n] ^ tmp.c[n-16];

	return 16+len+residue;
}

size_t CRYPTO_cts128_decrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], cbc128_f cbc)
{	size_t residue;
	union { size_t align; unsigned char c[32]; } tmp;

	if (len<=16) return 0;

	if ((residue=len%16) == 0) residue = 16;

	len -= 16+residue;

	if (len) {
		(*cbc)(in,out,len,key,ivec,0);
		in  += len;
		out += len;
	}

	memset(tmp.c,0,sizeof(tmp));
	/* this places in[16] at &tmp.c[16] and decrypted block at &tmp.c[0] */
	(*cbc)(in,tmp.c,16,key,tmp.c+16,0);

	memcpy(tmp.c,in+16,residue);
	(*cbc)(tmp.c,tmp.c,32,key,ivec,0);
	memcpy(out,tmp.c,16+residue);
	return 16+len+residue;
}

size_t CRYPTO_nistcts128_decrypt(const unsigned char *in, unsigned char *out,
			size_t len, const void *key,
			unsigned char ivec[16], cbc128_f cbc)
{	size_t residue;
	union { size_t align; unsigned char c[32]; } tmp;

	if (len<16) return 0;

	residue=len%16;

	if (residue==0) {
		(*cbc)(in,out,len,key,ivec,0);
		return len;
	}

	len -= 16+residue;

	if (len) {
		(*cbc)(in,out,len,key,ivec,0);
		in  += len;
		out += len;
	}

	memset(tmp.c,0,sizeof(tmp));
	/* this places in[16] at &tmp.c[16] and decrypted block at &tmp.c[0] */
	(*cbc)(in+residue,tmp.c,16,key,tmp.c+16,0);

	memcpy(tmp.c,in,residue);
	(*cbc)(tmp.c,tmp.c,32,key,ivec,0);
	memcpy(out,tmp.c,16+residue);
	return 16+len+residue;
}