Encrypt File Without PGP

How can I encrypt a file without using PGP?

Use the Unix crypt command.

This requires an agreed on password shared between those who will have access to the file. crypt encrypts and decrypts the contents of a file. crypt reads from the standard input and writes on the standard output. The password is a key that selects a particular transformation. If no password is given, crypt demands a key from the terminal and turns off printing while the key is being typed in. crypt encrypts and decrypts with the same key:

example% crypt password < clear.file > encrypted.file
example% crypt password < encrypted.file | more

will display the contents of clear.file.