<Tr> <Td> Key 2: </Td> <Td> CATCATCATCAT </Td> </Tr> <Tr> <Td> Ciphertext: </Td> <Td> IHSQIRIHCQCU </Td> </Tr> <P> Encrypting twice, first with the key GO and then with the key CAT is the same as encrypting once with a key produced by encrypting one key with the other . </P> <Table> <Tr> <Td> Plaintext: </Td> <Td> GOGOGO </Td> </Tr> <Tr> <Td> Key: </Td> <Td> CATCAT </Td> </Tr> <Tr> <Td> Ciphertext: </Td> <Td> IOZQGH </Td> </Tr> </Table>

What is the meaning of the key word square when used in the context of units