Damgård–Jurik Cryptosystem is a generalization of the Paillier cryptosystem , which is a additive homomorphic cryptosystem . Please see this paper for its mathematical proof.

For two message m1, m2, there exists

D(E(m1,r1)^m2*g^m2mod n²) = m1 * m2 mod n²

D(E(m1,r,)*E(m2,r2)mod n²) = (m1 + m2) mod n

For more details of Damgård–Jurik Cryptosystem, please see this paper

This library is for research on AHE or its applications, there may be bugs that i overlook.

The GNU Multiple Precision Arithmetic Library (GMP) is used for the underlying number theoretic operations, so you will need to have that installed before building it.

####Install You can build this library and include header file into your project or you can copy the source and header file to your project.

To build this library

cmake ./
make
make install

####Usage Here we show a example to select a plaintext, please see header file for more info.

#include <damgard_jurik.h>
//Here we use libsodium as random number generator
#include <sodium>

damgard_jurik dj = damgard_jurik(50, 1024, randombytes_buf);
damgard_jurik_plaintext_t text_1 = damgard_jurik_plaintext_t("abc");
damgard_jurik_plaintext_t text_2 = damgard_jurik_plaintext_t("efg");

damgard_jurik_plaintext_t sec_1 = damgard_jurik_plaintext_t((unsigned long)0);
damgard_jurik_plaintext_t sec_2 = damgard_jurik_plaintext_t((unsigned long)1);

damgard_jurik_ciphertext_t *c_1 = dj.encrypt(&sec_1, 10);
damgard_jurik_ciphertext_t *c_2 = dj.encrypt(&sec_2, 10);

damgard_jurik_ciphertext_t c_3 = (*c_1^*text_1_c) * (*c_2^*text_2_c);
damgard_jurik_plaintext_t *se_p = dj.decrypt(&c_3);
unsigned char *select_text = se_p->to_bytes();