@Test
    void x25519_private_key_serialization_roundtrip_maintains_original_structure() {
        var privHex = "77076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c2a";
        var priv = xecPrivFromHex(privHex);
        assertEquals(privHex, xecHexFromPriv(priv));

        // Base 64
        var privB64 = KeyUtils.toBase64EncodedX25519PrivateKey(priv);
        var priv2 = KeyUtils.fromBase64EncodedX25519PrivateKey(privB64);
        assertEquals(privHex, xecHexFromPriv(priv2));

        // Base 58
        var privB58 = KeyUtils.toBase58EncodedX25519PrivateKey(priv);
        var priv3 = KeyUtils.fromBase58EncodedX25519PrivateKey(privB58);
        assertEquals(privHex, xecHexFromPriv(priv3));
    }
RFC 7748 Section 6.1, Curve25519 Diffie-Hellman test vector
security-utils/src/test/java/com/yahoo/security/KeyUtilsTest.java