Provided is a method, system, and program for encoding and decoding input data. A key is generated comprising a list of a plurality of binary values, wherein the key is available to a user during decoding. The input data is encoded by using the key to initialize a replacement list. A determination is made whether to replace strings in the input data with a string reference to a matching string value, wherein the input data not replaced with reference to one matching string value comprises one or more literals. Each literal is replaced with a literal reference to one entry in the replacement list matching the literal. The encoded input data is decoded by accessing the generated key in response to user input and using the accessed key to decode the literals replaced with literal references to entries in the replacement list.