You must be talking about the Unix utility and not the C library since crypt is a built-in perl function.

Good encryption algorithms are needed when the algorithm itself is known. This is the case for both symmetrical and asymmetrical encryption. It sounds like you are just trying to obscure the data from a would be bad guy. In this case, you can engineer any data obscure solution you want. In other words, your algorithm itself can be the shared secret.

For example: Assume you have a very large book where every given word you want to encrypt appears multiple times. You could make your message a secret by replacing each word with the page number and number of words from the beginning where the word appears. Now "11, 5" only means something if both parties know which book is being used. Changing the books regularly in an "out of band" process adds to the difficulty in learning the secret.