}
+/**
+ * Computes a new PeerIdentity using the Chord formula.
+ * new_peer_identity = ((my_identity + pow(2,i)) mod (pow(2,m)
+ * where m, size of struct GNUNET_PeerIdentity in bits.
+ * i, 0 <= i <= m
+ * @param my_identity original PeerIdentity
+ * @param value of i.
+ * @return finger_identity
+ */
+struct GNUNET_PeerIdentity *
+GNUNET_CRYPTO_compute_finger_identity(struct GNUNET_PeerIdentity *my_identity, unsigned int index)
+{
+ gcry_mpi_t my_identity_mpi;
+ gcry_mpi_t finger_identity_mpi;
+ gcry_mpi_t add;
+ gcry_mpi_t mod;
+ gcry_error_t rc;
+ struct GNUNET_PeerIdentity *finger_identity;
+ size_t read = 0;
+ size_t write = 0;
+
+ finger_identity = GNUNET_malloc(sizeof(struct GNUNET_PeerIdentity));
+
+ /* Initialize my_identity_mpi. */
+ my_identity_mpi = gcry_mpi_new(8*sizeof(struct GNUNET_PeerIdentity));
+
+ /* Copy my_identity into my_id */
+ if(0 != (rc = gcry_mpi_scan(&my_identity_mpi, GCRYMPI_FMT_USG, my_identity->public_key.q_y,
+ sizeof(struct GNUNET_PeerIdentity), &read)))
+ {
+ LOG_GCRY (GNUNET_ERROR_TYPE_DEBUG, "gcry_mpi_scan", rc);
+ GNUNET_free(finger_identity);
+ return NULL;
+ }
+
+ /* Initialize finger_identity_mpi */
+ finger_identity_mpi = gcry_mpi_new(8*sizeof(struct GNUNET_PeerIdentity));
+
+ /* Initialize add */
+ add = gcry_mpi_new(8*sizeof(struct GNUNET_PeerIdentity));
+
+ /* Set the index bit in add.*/
+ gcry_mpi_set_bit(add,index);
+
+ /* Initialize mod */
+ mod = gcry_mpi_new(8*sizeof(struct GNUNET_PeerIdentity) + 1);
+ gcry_mpi_set_bit(mod,257);
+ gcry_mpi_sub_ui(mod,mod,(unsigned long)1);
+
+
+ /* finger_identity_mpi = (my_identity_mpi + add) % mod */
+ gcry_mpi_addm(finger_identity_mpi,my_identity_mpi,add,mod);
+
+
+ /* Copy finger_identity_mpi to finger_identity */
+ if(0 != (rc = gcry_mpi_print(GCRYMPI_FMT_USG,finger_identity->public_key.q_y,
+ 32,&write,finger_identity_mpi)))
+ {
+ LOG_GCRY (GNUNET_ERROR_TYPE_DEBUG, "gcry_mpi_print", rc);
+ GNUNET_free(finger_identity);
+ return NULL;
+ }
+
+ return finger_identity;
+}
+
+
/**
* Derive a public key from a given public key and a label.
* Essentially calculates a public key 'V = H(l,P) * P'.
*
* @param pub original public key
- * @param label label to use for key deriviation
+ * @param label label to use for key derivation
* @param context additional context to use for HKDF of 'h';
* typically the name of the subsystem/application
* @param result where to write the derived public key
q = gcry_mpi_ec_get_point ("q", ctx, 0);
GNUNET_assert (q);
- /* calulcate h_mod_n = h % n */
+ /* calculate h_mod_n = h % n */
h = derive_h (pub, label, context);
n = gcry_mpi_ec_get_mpi ("n", ctx, 1);
h_mod_n = gcry_mpi_new (256);