Encryption and decryption purely

I have a string of length 64 characters, I have to convert that into string of length 16 characters. Can you please guide me through the encryption method which encrypts the string of 64 characters into string of 16 characters and also when I decrypt the 16 characters string, I need to get the 64 characters strin开发者_Python百科g back.

You can't.

Generally, you can't put 64 bytes (or characters) of information into 16 bytes (or characters) without losing some data.

You can try to compress it and if you're lucky the data compresses to 16 bytes or less, but that depends on the input and will definitely not work on all input.