verify that taddr privkeys are base58

src/settings.cpp

@@ -441,8 +441,11 @@ bool Settings::isValidTransparentPrivateKey(QString pk) {
 
     // TODO: can a taddr privkey start with anything else?
     if (pk.startsWith("U") || pk.startsWith("5") || pk.startsWith("L") || pk.startsWith("K") || pk.startsWith("7")) {
-        // TODO: verify only contains base58 characters
-        return true;
+        // verify only contains base58 characters
+        QRegExp exp("^[U5LK7][123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz]{51,52}$",  Qt::CaseSensitive);
+        bool valid = exp.exactMatch(pk);
+        if(!valid) { DEBUG("privkey invalid, not base58"); }
+        return valid;
     } else {
         DEBUG("privkey invalid, wrong prefix");
         return false;