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A Simple Tutorial for EMP-toolkit

Basic Primitives

Pseudorandom generator

PRG is implemented as AES-NI in the CTR mode. Usage is presented as the following code sample.

PRG prg;//using a secure random seed

int rand_int, rand_ints[100];
block rand_block[3];
mpz_t integ;mpz_init(integ);

prg.random_data(&rand_int, sizeof(rand_int)); //fill rand_int with 32 random bits
prg.random_block(rand_block, 3);	      //fill rand_block with 128*3 random bits

prg.reseed(&rand_block[1]);                   //reset the seed and counter in prg
prg.random_data_unaligned(rand_ints+2, sizeof(int)*98);  //when the array is not 128-bit-aligned
prg.random_mpz(integ, 1024);                  //random number with 1024 bits.

Pseudorandom permutation

PRP is implemented based on AES-NI. Code sample:

block key;
PRG().random_block(&key,1)
PRP prp(&key); //if no parameter is provided, a public, fixed key will be used

block rand_block[3], b3[3];
int rand_ints[100];

prp.permute_block(rand_block, 3);//applying pi on each block of data
prp.permute_data(rand_ints, sizeof(int)*100);

block b2 = prp.H(rand_block[1], 1); //b2 = pi(r)\xor r, where r = doubling(random_block)\xor 1

prp.H<3>(b3, rand_block, 0);// apply the above H on three blocks using counter 0, 1, and 2 resp.

Hash function

Essentially a wrapper of <openssl/sha.h>

Hash hash;

char * data = new char[1024*1024], dig[Hash::DIGEST_SIZE];

hash.put(data, 1024*1024);
hash.digest(dig);

Commitment

Commitment c;

char * data = new char[1024*1024];
Com com;
Decom decom;

c.commit(decom, com, data, 1024*1024); // commit, will fill values decom and com
assert(c.open(decom, com, data, 1024*1024)); // open, return if the decommitment is valid or not