verify(configuration, atLeastOnce()).getOemEncoding();
    }

    @Test
    @DisplayName("E: splits 7-byte keys into 8-byte DES blocks and concatenates")
    void testE_blockSplitConsistency() throws ShortBufferException {
        // Arrange
        byte[] key14 = hex("01020304050607 11121314151617"); // two 7-byte chunks
        byte[] key7 = Arrays.copyOfRange(key14, 0, 7);