A 3-Way Crypto Lib is a specialized cryptographic library designed A 3-Way Crypto Lib is a specialized cryptographic library designed to facilitate secure interactions among three distinct parties. Its primary goal is to enable these parties to perform collaborative computations or exchange data while maintaining the confidentiality and integrity of their individual inputs and outputs.

It often leverages techniques like Multi-Party Computation (MPC), threshold cryptography, or secure key exchange protocols. This ensures that no single party, nor any two combined, can fully reconstruct the private data of the third party.

It builds trust in environments where direct data sharing is undesirable due to privacy concerns. Common applications include secure three-party voting, private data analytics, secure auctions, or distributed key generation where a quorum of two out of three parties is needed.

Essentially, it's a toolkit for creating robust, privacy-preserving systems involving three entities.

/********************************************************************\
* *
* C specification of the threeway block cipher *
* *
\********************************************************************/

#define STRT_E 0x0b0b /* round constant of first encryption round */
#define STRT_D 0xb1b1 /* round constant of first decryption round */
#define NMBR 11 /* number of rounds is 11 */

#ifdef __alpha /* Any other 64-bit machines? */
typedef unsigned int word32;
#else
typedef unsigned long word32;
#endif

/* the program only works correctly if long = 32bits */

void mu(word32 *a) /* inverts the order of the bits of a */
{
int i ;
word32 b[3] ;

b[0] = b[1] = b[2] = 0 ;
for( i=0 ; i<32 ; i++ )
{
b[0] <<= 1 ; b[1] <<= 1 ; b[2] <<= 1 ;
if(a[0]&1) b[2] |= 1 ;
if(a[1]&1) b[1] |= 1 ;
if(a[2]&1) b[0] |= 1 ;
a[0] >>= 1 ; a[1] >>= 1 ; a[2] >>= 1 ;
}

a[0] = b[0] ; a[1] = b[1] ; a[2] = b[2] ;
}

void gamma(word32 *a) /* the nonlinear step */
{
word32 b[3] ;

b[0] = a[0] ^ (a[1]|(~a[2])) ;
b[1] = a[1] ^ (a[2]|(~a[0])) ;
b[2] = a[2] ^ (a[0]|(~a[1])) ;

a[0] = b[0] ; a[1] = b[1] ; a[2] = b[2] ;
}


void theta(word32 *a) /* the linear step */
{
word32 b[3];

b[0] = a[0] ^ (a[0]>>16) ^ (a[1]<<16) ^ (a[1]>>16) ^ (a[2]<<16) ^
(a[1]>>24) ^ (a[2]<<8) ^ (a[2]>>8) ^ (a[0]<<24) ^
(a[2]>>16) ^ (a[0]<<16) ^ (a[2]>>24) ^ (a[0]<<8) ;
b[1] = a[1] ^ (a[1]>>16) ^ (a[2]<<16) ^ (a[2]>>16) ^ (a[0]<<16) ^
(a[2]>>24) ^ (a[0]<<8) ^ (a[0]>>8) ^ (a[1]<<24) ^
(a[0]>>16) ^ (a[1]<<16) ^ (a[0]>>24) ^ (a[1]<<8) ;
b[2] = a[2] ^ (a[2]>>16) ^ (a[0]<<16) ^ (a[0]>>16) ^ (a[1]<<16) ^
(a[0]>>24) ^ (a[1]<<8) ^ (a[1]>>8) ^ (a[2]<<24) ^
(a[1]>>16) ^ (a[2]<<16) ^ (a[1]>>24) ^ (a[2]<<8) ;

a[0] = b[0] ; a[1] = b[1] ; a[2] = b[2] ;
}

void pi_1(word32 *a)
{
a[0] = (a[0]>>10) ^ (a[0]<<22);
a[2] = (a[2]<<1) ^ (a[2]>>31);
}

void pi_2(word32 *a)
{
a[0] = (a[0]<<1) ^ (a[0]>>31);
a[2] = (a[2]>>10) ^ (a[2]<<22);
}

void rho(word32 *a) /* the round function */
{
theta(a) ;
pi_1(a) ;
gamma(a) ;
pi_2(a) ;
}

void rndcon_gen(word32 strt,word32 *rtab)
{ /* generates the round constants */
int i ;

for(i=0 ; i<=NMBR ; i++ )
{
rtab[i] = strt ;
strt <<= 1 ;
if( strt&0x10000 ) strt ^= 0x11011 ;
}
}

void encrypt(word32 *a, word32 *k)
{
int i ;
word32 rcon[NMBR+1] ;

rndcon_gen(STRT_E,rcon) ;
for( i=0 ; i<NMBR ; i++ )
{
a[0] ^= k[0] ^ (rcon[i]<<16) ;
a[1] ^= k[1] ;
a[2] ^= k[2] ^ rcon[i] ;
rho(a) ;
}
a[0] ^= k[0] ^ (rcon[NMBR]<<16) ;
a[1] ^= k[1] ;
a[2] ^= k[2] ^ rcon[NMBR] ;
theta(a) ;
}


void decrypt(word32 *a, word32 *k)
{
int i ;
word32 ki[3] ; /* the `inverse' key */
word32 rcon[NMBR+1] ; /* the `inverse' round constants */

ki[0] = k[0] ; ki[1] = k[1] ; ki[2] = k[2] ;
theta(ki) ;
mu(ki) ;

rndcon_gen(STRT_D,rcon) ;

mu(a) ;
for( i=0 ; i<NMBR ; i++ )
{
a[0] ^= ki[0] ^ (rcon[i]<<16) ;
a[1] ^= ki[1] ;
a[2] ^= ki[2] ^ rcon[i] ;
rho(a) ;
}
a[0] ^= ki[0] ^ (rcon[NMBR]<<16) ;
a[1] ^= ki[1] ;
a[2] ^= ki[2] ^ rcon[NMBR] ;
theta(a) ;
mu(a) ;
}

#ifdef TEST
#include <stdio.h>
#include <stdlib.h>
#define RAND32 ((word32)rand() << 17 ^ (word32)rand() << 9 ^ rand())

void printvec(word32 *a)
{
#ifdef __alpha
printf("%08x %08x %08x\n",a[2],a[1],a[0]) ;
#else
printf("%08lx %08lx %08lx\n",a[2],a[1],a[0]) ;
#endif
}

void main()
{
word32 vector[3], key[3],plain[3];
int i,j;

printf("3-way test run\n");
for (i = 0; i < 10; i++) {
for (j = 0; j < 3; j++) {
key[j] = RAND32;
plain[j]=vector[j] = RAND32;
}

printf("%3d\r", i);

fflush(stdout);

for (j = 0; j < 100; j++)
encrypt(vector,key);
for (j = 0; j < 100; j++)
decrypt(vector,key);

if (vector[0] != plain[0] || vector[1] != plain[1] ||
vector[2] != plain[2] ) {
fprintf(stderr, "\nError! i = %d\n", i);
exit(1);
}
}
printf("All tests passed.\n");
key[0]=4; key[1]=5; key[2]=6;
vector[0]=1; vector[1]=2; vector[2]=3;
encrypt(vector,key);
printvec(vector);
}
#endif

/* TEST VALUES
key : 00000000 00000000 00000000
plaintext : 00000001 00000001 00000001
ciphertext : ad21ecf7 83ae9dc4 4059c76e

key : 00000004 00000005 00000006
plaintext : 00000001 00000002 00000003
ciphertext : cab920cd d6144138 d2f05b5e

key : bcdef012 456789ab def01234
plaintext : 01234567 9abcdef0 23456789
ciphertext : 7cdb76b2 9cdddb6d 0aa55dbb

key : cab920cd d6144138 d2f05b5e
plaintext : ad21ecf7 83ae9dc4 4059c76e
ciphertext : 15b155ed 6b13f17c 478ea871
*/