u coord and x coord decode/encode

benchmark/main.c

@@ -16,7 +16,7 @@ main(int argc, char const *argv[])
 
 	hex_to_big("35fedf799f98ffaefb6fb91d77db7dc8fc8ff23fb5dc8fd77db7dc8ff3fc23f9", &a);
 	hex_to_big("3ace9e4bddc3029198a2be2ef84826ea23060628308a93ec90170e02654f33df", &b);
-	hex_to_big("1790f520c6645bdc6192b7da46c9382a5b9d8bf3e856a96e2c7018bc46f38534", &l);
+	hex_to_big("77076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c2a", &l);
 	hex_to_big("9ac6241f", &c);
 	hex_to_big("30591451fdebaf7c7c0457f47a3139c5db1bde9faacc877667c0457f47a3139c5db1b7c0457f47a3139c5db1b421df59658c21d04c88ebf9ed887b58bf7112dc", &d);
 
@@ -140,10 +140,20 @@ main(int argc, char const *argv[])
     big_null(&Gx);
     Gx.value[0] = Gx_25519;
 
+	/*
+		if bits % 8:
+		u[-1] &= (1<<(bits%8))-1
+	*/
+	uint8_t bytes[32];
+	u32_to_u8(l.value, bytes, 8);
+	big_null(&l);
+	mask_bytes(bytes);
+	u8_to_u32(bytes, l.value, 8);
 	start = clock();
 	ecp_mul_cst(&Gx, &l, &p, &r);
 	end = clock();
     cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;
+	decode_uc(r.value);
 	big_to_hex(&r);
 	printf("%lf\n", cpu_time_used);
 	printf("\n");

ecc/ecc_25519.c

@@ -1,9 +1,47 @@
 #include "ecc_25519.h"
 
+void
+get_rnd_bytes(uint8_t *bytes)
+{
+    FILE *fp = fopen("/dev/urandom", "rb");
+	for (int i = 0; i < 32; i++) {
+		int read = fread(&bytes[i], sizeof(uint8_t), 1, fp);
+		if (read == 0) {
+			return;
+		}
+	}
+	fclose(fp);
+}
+
+void
+mask_bytes(uint8_t *bytes)
+{
+	bytes[0] &= 248;
+	bytes[31] &= 127;
+	bytes[31] |= 64;
+}
+
+void
+get_scalar25519(uint32_t *scalar)
+{
+    uint8_t bytes[32];
+    get_rnd_bytes(bytes);
+	mask_bytes(bytes);
+	u8_to_u32(bytes, scalar, 8);
+}
+
+void
+decode_uc(uint32_t *uc)
+{
+    uint8_t bytes[32];
+    u32_to_u8(uc, bytes, 8);
+	u8_to_u32(bytes, uc, 8);
+}
+
 static inline void
 cst_swap(uint8_t swap, big_t* a, big_t *b)
 {
-    uint32_t dummy, mask = 0 - swap;
+    uint32_t dummy, mask = 0u - swap;
 
     for (int i = 0; i < 8; i++) {
         dummy = mask & (a->value[i] ^ b->value[i]);

ecc/ecc_25519.h

@@ -5,5 +5,9 @@
 #define Gx_25519 9u
 
 void ecp_mul_cst (big_t *, big_t *, big_t *, big_t *);
+void get_rnd_bytes(uint8_t *);
+void mask_bytes(uint8_t *);
+void get_scalar25519(uint32_t *);
+void decode_uc(uint32_t *);
 
 #endif

ecdh_aead_example.c

@@ -8,8 +8,11 @@ int main() {
     big_t prime, priv1, priv2;
     big_t own_pbk, own_pbk2, own_pbk3, own_pbk4;
 
-    big_rnd_dig(&priv1);
-	big_rnd_dig(&priv2);
+    big_null(&priv1);
+    big_null(&priv2);
+
+    get_scalar25519(priv1.value);
+    get_scalar25519(priv2.value);
 
     printf("\t\t\t --- ECDH - Key Agreement ---\nPrivate key1: ");
 	big_to_hex(&priv1);
@@ -23,10 +26,14 @@ int main() {
     big_null(&Gx);
     Gx.value[0] = Gx_25519;
     ecp_mul_cst(&Gx, &priv1, &prime, &own_pbk);
+
     ecp_mul_cst(&own_pbk, &priv2, &prime, &own_pbk2);
-
+    decode_uc(own_pbk2.value);
+
     ecp_mul_cst(&Gx, &priv2, &prime, &own_pbk3);
+
     ecp_mul_cst(&own_pbk3, &priv1, &prime, &own_pbk4);
+    decode_uc(own_pbk4.value);
 
 	printf("Public Key1: ");
     big_to_hex(&own_pbk);

utils.c

@@ -3,11 +3,10 @@
 void
 u32_to_u8(uint32_t *state, uint8_t *stream, unsigned len)
 {
-    for (int i = 0; i < len; i++) {
+    for (int i = len - 1; i >= 0; i--) {
         uint32_t curr = state[i];
-        for (int j = 0; j < 4; j++) {
-            int stream_index = i * 4 + (3 - j);
-            stream[stream_index] = (uint8_t)((curr >> (j * 8)) & 0xFFu);
+        for (int j = 3; j >= 0; j--) {
+            stream[(len - 1 - i) * 4 + (3 - j)] = (uint8_t)(curr >> (8 * j));
         }
     }
 }
@@ -16,10 +15,10 @@ void
 u8_to_u32(uint8_t *stream, uint32_t *arr, unsigned len)
 {
     for (int i = 0; i < len; i++) {
-        uint32_t acc = 0;
+        uint32_t sum = 0;
         for (int j = 0; j < 4; j++) {
-            acc += (uint32_t)(stream[i * 4 + j] << (j * 8));
+            sum += (uint32_t)stream[i * 4 + j] << (8 * j);
         }
-        arr[i] = acc;
+        arr[i] = sum;
     }
 }