1 files changed, 185 insertions, 0 deletions

diff --git a/src/util/crypto_paillier.c b/src/util/crypto_paillier.c
index b4c2df9b8..4697f14c3 100644
--- a/src/util/crypto_paillier.c
+++ b/src/util/crypto_paillier.c
@@ -28,4 +28,189 @@
 #include <gcrypt.h>
 #include "gnunet_util_lib.h"
 
+
+/**
+ * Create a freshly generated paillier public key.
+ *
+ * @param[out] public_key Where to store the public key?
+ * @param[out] private_key Where to store the private key?
+ */
+void
+GNUNET_CRYPTO_paillier_create (struct GNUNET_CRYPTO_PaillierPublicKey *public_key,
+                               struct GNUNET_CRYPTO_PaillierPrivateKey *private_key)
+{
+  gcry_mpi_t p;
+  gcry_mpi_t q;
+
+  gcry_mpi_t phi;
+  gcry_mpi_t n;
+
+  GNUNET_assert (NULL != (phi = gcry_mpi_new (GNUNET_CRYPTO_PAILLIER_BITS)));
+  GNUNET_assert (NULL != (n = gcry_mpi_new (GNUNET_CRYPTO_PAILLIER_BITS)));
+
+  p = q = NULL;
+
+  // Generate two distinct primes.
+  // The probability that the loop body
+  // is executed more than once is very low.
+  do {
+    if (NULL != p)
+      gcry_mpi_release (p);
+    if (NULL != q)
+      gcry_mpi_release (q);
+    // generate rsa modulus
+    GNUNET_assert (0 == gcry_prime_generate (&p, GNUNET_CRYPTO_PAILLIER_BITS / 2, 0, NULL, NULL, NULL,
+                                             GCRY_WEAK_RANDOM, 0));
+    GNUNET_assert (0 == gcry_prime_generate (&q, GNUNET_CRYPTO_PAILLIER_BITS / 2, 0, NULL, NULL, NULL,
+                                             GCRY_WEAK_RANDOM, 0));
+  } while (0 == gcry_mpi_cmp (p, q));
+  gcry_mpi_mul (n, p, q);
+  GNUNET_CRYPTO_mpi_print_unsigned (public_key, sizeof (struct GNUNET_CRYPTO_PaillierPublicKey), n);
+
+  // compute phi(n) = (p-1)(q-1)
+  gcry_mpi_sub_ui (p, p, 1);
+  gcry_mpi_sub_ui (q, q, 1);
+  gcry_mpi_mul (phi, p, q);
+
+  // lambda equals phi(n) in the simplified key generation
+  GNUNET_CRYPTO_mpi_print_unsigned (private_key->lambda, GNUNET_CRYPTO_PAILLIER_BITS / 8, phi);
+
+  // invert phi and abuse the phi mpi to store the result ...
+  GNUNET_assert (0 != gcry_mpi_invm (phi, phi, n));
+  GNUNET_CRYPTO_mpi_print_unsigned (private_key->mu, GNUNET_CRYPTO_PAILLIER_BITS / 8, phi);
+
+  gcry_mpi_release (p);
+  gcry_mpi_release (q);
+  gcry_mpi_release (phi);
+  gcry_mpi_release (n);
+}
+
+
+/**
+ * Encrypt a plaintext with a paillier public key.
+ *
+ * @param public_key Public key to use.
+ * @param plaintext Plaintext to encrypt.
+ * @param[out] ciphertext Encrytion of @a plaintext with @a public_key.
+ */
+void
+GNUNET_CRYPTO_paillier_encrypt (const struct GNUNET_CRYPTO_PaillierPublicKey *public_key,
+                                const struct GNUNET_CRYPTO_PaillierPlaintext *plaintext,
+                                struct GNUNET_CRYPTO_PaillierCiphertext *ciphertext)
+{
+  gcry_mpi_t n_square;
+  gcry_mpi_t r;
+  gcry_mpi_t g;
+  gcry_mpi_t c;
+
+  gcry_mpi_t n;
+  gcry_mpi_t m;
+
+
+  GNUNET_assert (0 != (n_square = gcry_mpi_new (0)));
+  GNUNET_assert (0 != (r = gcry_mpi_new (0)));
+  GNUNET_assert (0 != (g = gcry_mpi_new (0)));
+  GNUNET_assert (0 != (c = gcry_mpi_new (0)));
+
+  GNUNET_CRYPTO_mpi_scan_unsigned (&m, plaintext, sizeof (struct GNUNET_CRYPTO_PaillierPlaintext));
+  GNUNET_CRYPTO_mpi_scan_unsigned (&n, public_key, sizeof (struct GNUNET_CRYPTO_PaillierPublicKey));
+
+  gcry_mpi_mul (n_square, n, n);
+
+  // generate r < n
+  do
+  {
+    gcry_mpi_randomize (r, GNUNET_CRYPTO_PAILLIER_BITS, GCRY_WEAK_RANDOM);
+  }
+  while (gcry_mpi_cmp (r, n) >= 0);
+
+  // c = (n+1)^m mod n^2
+  gcry_mpi_add_ui (c, n, 1);
+  gcry_mpi_powm (c, c, m, n_square);
+  // r <- r^n mod n^2
+  gcry_mpi_powm (r, r, n, n_square);
+  // c <- r*c mod n^2
+  gcry_mpi_mulm (c, r, c, n_square);
+
+  GNUNET_CRYPTO_mpi_print_unsigned (ciphertext, sizeof *ciphertext, c);
+
+  gcry_mpi_release (n_square);
+  gcry_mpi_release (r);
+  gcry_mpi_release (m);
+  gcry_mpi_release (c);
+}
+
+
+/**
+ * Decrypt a paillier ciphertext with a private key.
+ *
+ * @param private_key Private key to use for decryption.
+ * @param public_key Public key to use for decryption.
+ * @param ciphertext Ciphertext to decrypt.
+ * @param[out] plaintext Decryption of @a ciphertext with @private_key.
+ */
+void
+GNUNET_CRYPTO_paillier_decrypt (const struct GNUNET_CRYPTO_PaillierPrivateKey *private_key,
+                                const struct GNUNET_CRYPTO_PaillierPublicKey *public_key,
+                                const struct GNUNET_CRYPTO_PaillierCiphertext *ciphertext,
+                                struct GNUNET_CRYPTO_PaillierPlaintext *plaintext)
+{
+  gcry_mpi_t m;
+  gcry_mpi_t mu;
+  gcry_mpi_t lambda;
+  gcry_mpi_t n;
+  gcry_mpi_t n_square;
+  gcry_mpi_t c;
+
+  GNUNET_assert (0 != (n_square = gcry_mpi_new (0)));
+  GNUNET_assert (0 != (m = gcry_mpi_new (0)));
+
+  GNUNET_CRYPTO_mpi_scan_unsigned (&lambda, private_key->lambda, sizeof private_key->lambda);
+  GNUNET_CRYPTO_mpi_scan_unsigned (&mu, private_key->mu, sizeof private_key->mu);
+  GNUNET_CRYPTO_mpi_scan_unsigned (&n, public_key, sizeof *public_key);
+  GNUNET_CRYPTO_mpi_scan_unsigned (&c, ciphertext, sizeof *ciphertext);
+
+  gcry_mpi_mul (n_square, n, n);
+  // m = c^lambda mod n^2
+  gcry_mpi_powm (m, c, lambda, n_square);
+  // m = m - 1
+  gcry_mpi_sub_ui (m, m, 1);
+  // m <- m/n
+  gcry_mpi_div (m, NULL, m, n, 0);
+  gcry_mpi_mulm (m, m, mu, n);
+
+  GNUNET_CRYPTO_mpi_print_unsigned (plaintext, sizeof *plaintext, m);
+
+  gcry_mpi_release (m);
+  gcry_mpi_release (mu);
+  gcry_mpi_release (lambda);
+  gcry_mpi_release (n);
+  gcry_mpi_release (n_square);
+  gcry_mpi_release (c);
+}
+
+
+/**
+ * Compute a ciphertext that represents the sum of the plaintext in @a x1 and @a x2
+ *
+ * Note that this operation can only be done a finite number of times
+ * before an overflow occurs.
+ *
+ * @param x1 Paillier cipher text.
+ * @param x2 Paillier cipher text.
+ * @param[out] result Result of the homomorphic operation.
+ * @return #GNUNET_OK if the result could be computed,
+ *         #GNUNET_SYSERR if no more homomorphic operations are remaining.
+ */
+int
+GNUNET_CRYPTO_paillier_hom_add (const struct GNUNET_CRYPTO_PaillierCiphertext *x1,
+                                const struct GNUNET_CRYPTO_PaillierCiphertext *x2,
+                                const struct GNUNET_CRYPTO_PaillierCiphertext *result)
+{
+  // not implemented yet
+  GNUNET_assert (0);
+  return GNUNET_SYSERR;
+}
+
+
 /* end of crypto_paillier.c */