private static void verifyB58InputSmallEnoughToBeX25519Key(String key) {
        if (key.length() > 64) { // a very wide margin...
            throw new IllegalArgumentException("Input Base58 is too large to represent an X25519 key");
        }
    }
Returns the bytes representing the BigInteger of the X25519 public key EC point U coordinate
security-utils/src/main/java/com/yahoo/security/KeyUtils.java