Made permutation a responsibility of cmix in the precomputation phase.

2 files changed, 42 insertions, 21 deletions

diff --git a/libcmix/cmix.c b/libcmix/cmix.c
index f6eb2e8..68a638f 100644
--- a/libcmix/cmix.c
+++ b/libcmix/cmix.c
@@ -120,13 +120,31 @@ enum cmix_error start_mix(struct CMixContext* ctx, size_t nr_participants) {
 	return alloc_mix(ctx);
 }
 
+enum cmix_error generate_permutation(struct CMixContext* ctx) {
+	ctx->permutation = (unsigned int*) calloc(ctx->nr_participants, sizeof(unsigned int));
+	for(unsigned int i = 0; i < ctx->nr_participants; ++i) {
+		ctx->permutation[i] = i;
+	}
+	
+	//Fisher-Yates shuffle
+	unsigned int temp = 0;
+	for(unsigned int i = ctx->nr_participants - 1; i > 0; --i) {
+		unsigned int rand = ctx->api.get_uniform_int(i+1);
+		temp = ctx->permutation[i];
+		ctx->permutation[i] = ctx->permutation[rand];
+		ctx->permutation[rand] = temp;
+	}
+
+	return no_error;
+}
+
 enum cmix_error initialize_mix_randomness(struct CMixContext* ctx) {
 	for(size_t i = 0; i < ctx->nr_participants; ++i) {
 		ctx->r[i] = ctx->api.get_group_element(true);
 		ctx->s[i] = ctx->api.get_group_element(true);
-		ctx->permutation[i] = i;
 	}
-	return no_error;
+	
+	return generate_permutation(ctx);
 }
 
 enum cmix_error generate_random_message(struct CMixContext* ctx, char* buffer) {
@@ -185,27 +203,30 @@ enum cmix_error encrypt_r_and_multiply(struct CMixContext const* ctx, char* rand
 	return no_error;
 }
 
-enum cmix_error multiply_encrypted_s(struct CMixContext const* ctx, char* r_out_buffer, char* m_out_buffer, char const* r_in_buffer, char const* m_in_buffer, size_t index) {
+enum cmix_error permute_and_multiply_encrypted_s(struct CMixContext const* ctx, char** random_buffer, char** message_buffer, char const** random_element, char const** message_element, size_t nr_elements) {
 	size_t el_size = get_group_element_array_size(ctx);
 	
-	GroupElement random_r = ctx->api.array_to_element(r_in_buffer, el_size, true);
-	GroupElement message_r = ctx->api.array_to_element(m_in_buffer, el_size, true);
-	
-	GroupElement random_s;
-	GroupElement message_s;
-	
-	ctx->api.encrypt(&random_s, &message_s, ctx->s[ctx->permutation[index]], ctx->network_key);
-	
-	GroupElement random_pirs = ctx->api.multiply(random_r, random_s, true);
-	GroupElement message_pirs = ctx->api.multiply(message_r, message_s, true);
-	
-	element_to_buffer(ctx, r_out_buffer, random_pirs);
-	element_to_buffer(ctx, m_out_buffer, message_pirs);
+	for(size_t i = 0; i < nr_elements; ++i) {
+		unsigned int new_pos = ctx->permutation[i];
+		GroupElement random_r = ctx->api.array_to_element(random_element[i], el_size, true);
+		GroupElement message_r = ctx->api.array_to_element(message_element[i], el_size, true);
 	
-	ctx->api.free_group_element(random_r);
-	ctx->api.free_group_element(message_r);
-	ctx->api.free_group_element(random_s);
-	ctx->api.free_group_element(message_s);
+		GroupElement random_s;
+		GroupElement message_s;
+		
+		ctx->api.encrypt(&random_s, &message_s, ctx->s[new_pos], ctx->network_key);
+		
+		GroupElement random_pirs = ctx->api.multiply(random_r, random_s, true);
+		GroupElement message_pirs = ctx->api.multiply(message_r, message_s, true);
+		
+		element_to_buffer(ctx, random_buffer[new_pos], random_pirs);
+		element_to_buffer(ctx, message_buffer[new_pos], message_pirs);
+		
+		ctx->api.free_group_element(random_r);
+		ctx->api.free_group_element(message_r);
+		ctx->api.free_group_element(random_s);
+		ctx->api.free_group_element(message_s);
+	}
 	
 	return no_error;
 }
diff --git a/libcmix/cmix.h b/libcmix/cmix.h
index 89a6ad3..53212fe 100644
--- a/libcmix/cmix.h
+++ b/libcmix/cmix.h
@@ -110,7 +110,7 @@ enum cmix_error encrypt_r(struct CMixContext const* ctx, char* random_buffer, ch
 
 enum cmix_error encrypt_r_and_multiply(struct CMixContext const* ctx, char* random_buffer, char* message_buffer, char const* random_element, char const* message_element, size_t index);
 
-enum cmix_error multiply_encrypted_s(struct CMixContext const* ctx, char* r_out_buffer, char* m_out_buffer, char const* r_in_buffer, char const* m_in_buffer, size_t index);
+enum cmix_error permute_and_multiply_encrypted_s(struct CMixContext const* ctx, char** random_buffer, char** message_buffer, char const** random_element, char const** message_element, size_t nr_elements);
 
 enum cmix_error multiply_s(struct CMixContext const* ctx, char* out_buffer, char const* message, size_t index);