Support for ElGamal in FFI interface

* Adds `botan_pubkey_load_elgamal' and `botan_privkey_load_elgamal'
  functions to FFI interface.
* Adds test `ffi_test_elgamal'

2 files changed, 92 insertions, 1 deletions

diff --git a/src/lib/ffi/ffi.cpp b/src/lib/ffi/ffi.cpp
index 7cf69efb3..8e341d83d 100644
--- a/src/lib/ffi/ffi.cpp
+++ b/src/lib/ffi/ffi.cpp
@@ -26,6 +26,7 @@
 #include <botan/reducer.h>
 #include <botan/numthry.h>
 #include <botan/divide.h>
+#include <botan/elgamal.h>
 #include <cstring>
 #include <memory>
 
@@ -1422,6 +1423,57 @@ int botan_pubkey_load_dsa(botan_pubkey_t* key,
 #endif
    }
 
+int botan_pubkey_load_elgamal(botan_pubkey_t* key,
+                              botan_mp_t p, botan_mp_t g, botan_mp_t y)
+   {
+#if defined(BOTAN_HAS_ELGAMAL)
+   *key = nullptr;
+   try
+      {
+      Botan::DL_Group group(safe_get(p), safe_get(g));
+      *key = new botan_pubkey_struct(new Botan::ElGamal_PublicKey(group, safe_get(y)));
+      return 0;
+      }
+   catch(std::exception& exn)
+      {
+      log_exception(BOTAN_CURRENT_FUNCTION, exn.what());
+      }
+
+   return -1;
+#else
+   BOTAN_UNUSED(p);
+   BOTAN_UNUSED(q);
+   BOTAN_UNUSED(g);
+   BOTAN_UNUSED(x);
+   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
+#endif
+   }
+
+int botan_privkey_load_elgamal(botan_privkey_t* key,
+                               botan_mp_t p, botan_mp_t g, botan_mp_t x)
+   {
+#if defined(BOTAN_HAS_ELGAMAL)
+   *key = nullptr;
+   try
+      {
+      Botan::Null_RNG null_rng;
+      Botan::DL_Group group(safe_get(p), safe_get(g));
+      *key = new botan_privkey_struct(new Botan::ElGamal_PrivateKey(null_rng, group, safe_get(x)));
+      return 0;
+      }
+   catch(std::exception& e)
+      {
+      log_exception(BOTAN_CURRENT_FUNCTION, e.what());
+      }
+   return -1;
+#else
+   BOTAN_UNUSED(p);
+   BOTAN_UNUSED(g);
+   BOTAN_UNUSED(x);
+   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
+#endif
+   }
+
 namespace {
 
 Botan::BigInt botan_pubkey_do_get_field(const Botan::Public_Key& key,
diff --git a/src/lib/ffi/ffi.h b/src/lib/ffi/ffi.h
index 59e767385..8fb7ca832 100644
--- a/src/lib/ffi/ffi.h
+++ b/src/lib/ffi/ffi.h
@@ -175,7 +175,7 @@ typedef struct botan_rng_struct* botan_rng_t;
 *    "system": System_RNG, "user": AutoSeeded_RNG
 * Set rng_type to null or empty string to let the library choose
 *
-* TODO: replace rng_type with simple flags? 
+* TODO: replace rng_type with simple flags?
 */
 BOTAN_DLL int botan_rng_init(botan_rng_t* rng, const char* rng_type);
 
@@ -785,6 +785,45 @@ BOTAN_DLL int botan_pubkey_dsa_get_g(botan_mp_t d, botan_pubkey_t key);
 BOTAN_DLL int botan_pubkey_dsa_get_y(botan_mp_t y, botan_pubkey_t key);
 
 /*
+* Algorithm specific key operations: ElGamal
+*/
+
+/*
+* Loads ElGamal public key
+* @param key variable populated with key material
+* @param p prime order of a Z_p group
+* @param g group generator
+* @param y public key
+*
+* @pre key is NULL on input
+* @post function allocates memory and assigns to `key'
+*
+* @return 0 on success, a negative value on failure
+*/
+BOTAN_DLL int botan_pubkey_load_elgamal(botan_pubkey_t* key,
+                                        botan_mp_t p,
+                                        botan_mp_t g,
+                                        botan_mp_t y);
+
+/*
+* Loads ElGamal private key
+*
+* @param key variable populated with key material
+* @param p prime order of a Z_p group
+* @param g group generator
+* @param x private key
+*
+* @pre key is NULL on input
+* @post function allocates memory and assigns to `key'
+*
+* @return 0 on success, a negative value on failure
+*/
+BOTAN_DLL int botan_privkey_load_elgamal(botan_privkey_t* key,
+                                         botan_mp_t p,
+                                         botan_mp_t g,
+                                         botan_mp_t x);
+
+/*
 * Public Key Encryption
 */
 typedef struct botan_pk_op_encrypt_struct* botan_pk_op_encrypt_t;