From 6d55dcba54ceaccc9d90ea7c2f1746524a6e81e3 Mon Sep 17 00:00:00 2001
From: Dennis Brentjes <d.brentjes@gmail.com>
Date: Fri, 18 Nov 2016 12:47:35 +0100
Subject: Made permutation a responsibility of cmix in the precomputation
 phase.

---
 libcmix-crypto/api.h                           |  6 ++++++
 libcmix-crypto/elgamal/elgamal.c               |  1 +
 libcmix-crypto/elgamal/elgamal.h               |  2 ++
 libcmix-crypto/elgamal/gcrypt/gcrypt_elgamal.c | 26 ++++++++++++++++++++++++++
 4 files changed, 35 insertions(+)

(limited to 'libcmix-crypto')

diff --git a/libcmix-crypto/api.h b/libcmix-crypto/api.h
index d52ab95..caf97b6 100644
--- a/libcmix-crypto/api.h
+++ b/libcmix-crypto/api.h
@@ -105,6 +105,11 @@ typedef void (*Encrypter)(GroupElement*, GroupElement*, GroupElement, GroupEleme
  */
 typedef GroupElement (*Inverter)(GroupElement);
 
+/*!
+ *
+ */
+typedef unsigned int (*UniformIntGetter)(unsigned int);
+
 /*!
  *
  */
@@ -132,6 +137,7 @@ struct Api {
 	SharedKeyDeleter free_shared_key; ///< Pointer to shared key deleter function
 	Encrypter encrypt; ///< encrypt value with key;
 	Inverter invert; ///< Invert the group element;
+	UniformIntGetter get_uniform_int; ///< Get a uniform int [0 .. argument);
 	Deinitializer deinitialize; ///< Function that will deinitialize the crypto library.
 };
 
diff --git a/libcmix-crypto/elgamal/elgamal.c b/libcmix-crypto/elgamal/elgamal.c
index 7eea0f3..8f26a3c 100644
--- a/libcmix-crypto/elgamal/elgamal.c
+++ b/libcmix-crypto/elgamal/elgamal.c
@@ -22,6 +22,7 @@ struct Api get_elgamal_implementation()
 		.free_shared_key = elgamal_delete_shared_key,
 		.encrypt = elgamal_encrypt,
 		.invert = elgamal_invert,
+		.get_uniform_int = elgamal_get_uniform_int,
 		.deinitialize = elgamal_deinitialize
 	};
 }
diff --git a/libcmix-crypto/elgamal/elgamal.h b/libcmix-crypto/elgamal/elgamal.h
index 1054e3e..f937899 100644
--- a/libcmix-crypto/elgamal/elgamal.h
+++ b/libcmix-crypto/elgamal/elgamal.h
@@ -46,6 +46,8 @@ extern Encrypter elgamal_encrypt;
 
 extern Inverter elgamal_invert;
 
+extern UniformIntGetter elgamal_get_uniform_int;
+
 extern Deinitializer elgamal_deinitialize;
 
 /*!
diff --git a/libcmix-crypto/elgamal/gcrypt/gcrypt_elgamal.c b/libcmix-crypto/elgamal/gcrypt/gcrypt_elgamal.c
index 6a03fb1..e25ba72 100644
--- a/libcmix-crypto/elgamal/gcrypt/gcrypt_elgamal.c
+++ b/libcmix-crypto/elgamal/gcrypt/gcrypt_elgamal.c
@@ -284,6 +284,31 @@ GroupElement gcrypt_elgamal_invert(GroupElement const x) {
 	return inv_x;
 }
 
+unsigned int gcrypt_elgamal_get_uniform_int(unsigned int upper) {
+	unsigned int random_value;
+	
+	if(upper == 0) {
+		void* buffer = gcry_random_bytes_secure(nr_bytes, GCRY_STRONG_RANDOM);
+
+		memcpy(&random_value, buffer, sizeof(unsigned int));
+		
+		gcry_free(buffer);
+		return random_value;
+	}
+	
+	unsigned int lower = -upper % upper;
+	do {
+		void* buffer = gcry_random_bytes_secure(nr_bytes, GCRY_STRONG_RANDOM);
+
+		memcpy(&random_value, buffer, sizeof(unsigned int));
+		
+		if (random_value >= lower)
+			return random_value % upper;
+		
+		gcry_free(buffer);
+	} while(true);
+}
+
 void gcrypt_elgamal_deinitialize(void) {
 	gcry_mpi_release(p);
 	gcry_mpi_release(q);
@@ -308,4 +333,5 @@ SharedKeyDeriver elgamal_derive_shared_key = &gcrypt_elgamal_derive_shared_key;
 SharedKeyDeleter elgamal_delete_shared_key = &gcrypt_elgamal_delete_shared_key;
 Encrypter elgamal_encrypt = &gcrypt_elgamal_encrypt;
 Inverter elgamal_invert = &gcrypt_elgamal_invert;
+UniformIntGetter elgamal_get_uniform_int = &gcrypt_elgamal_get_uniform_int;
 Deinitializer elgamal_deinitialize = &gcrypt_elgamal_deinitialize;
\ No newline at end of file
-- 
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