Complete rewrite of XP Algorithm (w/ comments). Now fully optimized and readable

src/util.cpp

@@ -84,4 +84,19 @@ EC_GROUP *initializeEllipticCurve(
     BN_CTX_free(context);
 
     return eCurve;
+}
+
+int BN_bn2lebin(const BIGNUM *a, unsigned char *to, int tolen) {
+    if (a == nullptr || to == nullptr)
+        return 0;
+
+    int len = BN_bn2bin(a, to);
+
+    if (len > tolen)
+        return -1;
+
+    // Choke point inside BN_bn2lebinpad: OpenSSL uses len instead of tolen.
+    endian(to, tolen);
+
+    return len;
 }