/*
 * Copyright © 2002 Vita Nuova Holdings Limited.  All rights reserved.
 */
#include <lib9.h>
#include <bio.h>

/* CBC, ECB, integrate, SSL */

#define KEYLEN	52

#define	MODA	0x10000
#define	MODM	0x10001
#define	MASKA	(MODA-1)

#define 	OP1(x, y)		((x) ^ (y))
#define	OP2(x, y)		(((x) + (y)) & MASKA)
#define 	OP3(x, y)		mod(x, y)

#define	OP2INV(x)	(-(x))
#define	OP3INV(x)	inv(x)

#define BIGEND(k, i)	((k[i]<<8)|k[i+1])
#define MSB(x)		((x)>>8)
#define LSB(x)		((x)&0xff)

static ushort
mod(ushort x, ushort y)
{
	ushort q, r;
	uint z;

	if (x == 0)
		return 1-y;
	if (y == 0)
		return 1-x;
	z = (uint)x*(uint)y;
	q = z >> 16;
	r = z & MASKA;
	return r-q+(r<q);
}

static ushort 
inv(ushort x)
{
	int q, r0, r1, r2, v0, v1, v2;

	if (x <= 1)
		return x;
	r0 = MODM;
	r1 = x;
	v0 = 0;
	v1 = 1;
	while (r1 != 0) {
		q = r0/r1;
		r2 = r0-q*r1;
		v2 = v0-q*v1;
		r0 = r1;
		r1 = r2;
		v0 = v1;
		v1 = v2;
	}
	if (v0 < 0)
		v0 += MODM;
	return v0 & MASKA;
}

static void
idea_key_setup_decrypt(ushort ek[KEYLEN], ushort dk[KEYLEN])
{
	int i;

	for (i = 0; i < 54; i += 6) {
		dk[i] = OP3INV(ek[48-i]);
		dk[i+1] = OP2INV(ek[50-i]);
		dk[i+2] = OP2INV(ek[49-i]);
		dk[i+3] = OP3INV(ek[51-i]);
		if (i < 48) {
			dk[i+4] = ek[46-i];
			dk[i+5] = ek[47-i];
		}
	}
}

void
idea_key_setup(uchar key[16], ushort ek[2*KEYLEN])
{
	int i, j;
	ushort tmp, *e = ek;

	for (i = 0; i < 8; i++)
		ek[i] = BIGEND(key, 2*i);
	for (i = 8, j = 1; i < KEYLEN; i++, j++) {
		ek[i] = (e[j&7]<<9)|(e[(j+1)&7]>>7);
		if (((i+1) & 7) == 0)
			e += 8;
	}
	tmp = ek[49];
	ek[49] = ek[50];
	ek[50] = tmp;
	idea_key_setup_decrypt(ek, &ek[KEYLEN]);
}

void
idea_cipher(ushort key[2*KEYLEN], uchar text[8], int decrypting)
{
	int i;
	ushort *k;
	ushort x[4];
	ushort tmp, yout, zout;

	k = decrypting ? &key[KEYLEN] : key;
	for (i = 0; i < 4; i++)
		x[i] = BIGEND(text, 2*i);
	for (i = 0; i < 17; i++) {
		if (!(i&1)) {		/* odd round */
			x[0] = OP3(x[0], k[3*i]);
			tmp = OP2(x[2], k[3*i+2]);
			x[2] = OP2(x[1], k[3*i+1]);
			x[3] = OP3(x[3], k[3*i+3]);
			x[1] = tmp;
		}
		else {
			tmp = OP3(k[3*i+1], OP1(x[0], x[1]));
			yout = OP3(OP2(tmp, OP1(x[2], x[3])), k[3*i+2]);
			zout = OP2(tmp, yout);
			x[0] = OP1(x[0], yout);
			x[1] = OP1(x[1], yout);
			x[2] = OP1(x[2], zout);
			x[3] = OP1(x[3], zout);
		}
	}
	for (i = 0; i < 4; i++) {
		text[2*i] = MSB(x[i]); 
		text[2*i+1] = LSB(x[i]);
	}
}

static void
decerr(char *s)
{
	fprint(2, "decrypt error: %s (wrong password ?)\n", s);
	exits("decrypt");
}

void
main(int argc, char **argv)
{
/*
	uchar key[] = { 0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04,
			        0x00, 0x05, 0x00, 0x06, 0x00, 0x07, 0x00, 0x08 };
	uchar plain[] = { 0x00, 0x00, 0x00, 0x01, 0x00, 0x02, 0x00, 0x03 };
	uchar cipher[] = { 0x11, 0xFB, 0xED, 0x2B, 0x01, 0x98, 0x6D, 0xE5 };
	uchar tmp[8];
*/
	ushort edkey[2*KEYLEN];
	uchar obuf[8], buf[8], key[16];
	long i, m, n, om;
	int dec, stdin = 0, stdout = 1;
	Biobuf *bin, *bout;

/*
	memcpy(tmp, plain, 8);
	idea_key_setup(key, edkey);
	idea_cipher(edkey, tmp, 0);
	if (memcmp(tmp, cipher, 8)) {
		print("encrypt wrong\n");
		exits("");
	}
	idea_cipher(edkey, tmp, 1);
	if (memcmp(tmp, plain, 8)) {
		print("decrypt wrong\n");
		exits("");
	}
*/

	if((argc != 3 && argc != 4) || (strcmp(argv[1], "-e") != 0 && strcmp(argv[1], "-d") != 0) || strlen(argv[2]) != 16){
		fprint(2, "usage: idea -[e | d] <16 char key> [inputfile]\n");
		exits("usage");
	}
	dec = strcmp(argv[1], "-d") == 0;
	if(argc == 4){
		char s[128];

		stdin = open(argv[3], OREAD);
		if(stdin < 0){
			fprint(2, "cannot open %s\n", argv[3]);
			exits("");
		}
		strcpy(s, argv[3]);
		if(dec){
			if(strcmp(s+strlen(s)-3, ".id") != 0){
				fprint(2, "input file not a .id file\n");
				exits("");
			}
			s[strlen(s)-3] = '\0';
		}
		else
			strcat(s, ".id");
		stdout = create(s, OWRITE, 0666);
		if(stdout < 0){
			fprint(2, "cannot create %s\n", s);
			exits("");
		}
	}
	for(i = 0; i < 16; i++)
		key[i] = argv[2][i];
	idea_key_setup(key, edkey);
	m = om = 0;
	bin = (Biobuf*)malloc(sizeof(Biobuf));
	bout = (Biobuf*)malloc(sizeof(Biobuf));
	Binit(bin, stdin, OREAD);
	Binit(bout, stdout, OWRITE);
	for(;;){
		n = Bread(bin, &buf[m], 8-m);
		if(n <= 0)
			break;
		m += n;
		if(m == 8){
			idea_cipher(edkey, buf, dec);
			if(dec){	/* leave last block around */
				if(om > 0)
					Bwrite(bout, obuf, 8);
				memcpy(obuf, buf, 8);
				om = 8;
			}
			else
				Bwrite(bout, buf, 8);
			m = 0;
		}
	}
	if(dec){
		if(om != 8)
			decerr("no last block");
		if(m != 0)
			decerr("last block not 8 bytes long");
		m = obuf[7];
		if(m < 0 || m > 7)
			decerr("bad modulus");
		for(i = m; i < 8-1; i++)
			if(obuf[i] != 0)
				decerr("byte not 0");
		Bwrite(bout, obuf, m);
	}
	else{
		for(i = m; i < 8; i++)
			buf[i] = 0;
		buf[7] = m;
		idea_cipher(edkey, buf, dec);
		Bwrite(bout, buf, 8);
	}
	Bflush(bout);
	Bterm(bin);
	Bterm(bout);
}