Kamasutra cipher. Write a filter Kama sutra Cipher that takes two strings as command-line argument (the key strings), then reads strings (separated by whitespace) from standard input, substitutes for...

Kamasutra cipher. Write a filter Kama sutra Cipher that takes two strings as command-line argument (the key strings), then reads strings (separated by whitespace) from standard input, substitutes for each letter as specified by the key strings, and prints the result to standard output. This operation is the basis for one of the earliest known cryptographic systems. The condition on the key strings is that they must be of equal length and that any letter in standard input must appear in exactly one of them. For example, if the two keys are THEQUICKBROWN and FXJMPSVLAZYDG, then we make the table

which tells us that we should substitute F for T, T for F, H for X, X for H, and so forth when filtering standard input to standard output. The message is encoded by replacing each letter with its pair. For example, the message MEET AT ELEVEN is encoded as QJJF BF JKJCJG. The person receiving the message can use the same keys to get the message back.