When should I compress data for encryption?

When you plan to archive large amounts of encrypted data, you might consider compressing the data (for example, to reduce the number of tape volumes you might need).

Some tape devices make use of their own compression when you store data. By definition, data that is encrypted should not be compressible; if you can compress encrypted data it is probably not well encrypted. You might want to compress your data before you encrypt it using the COMPRESSION option of Encryption Services.

If you plan to use the Java-based Client of the Encryption Facility for z/OS Client to decrypt z/OS® data, note that it cannot decrypt data that has been compressed from the CSDFILEN batch program. On any supported z/OS platform, you can use the Decryption for z/OS Client of Encryption Facility for z/OS Client to decompress and decrypt data that has been encrypted through CSDFILEN.

CSDFILEN tries to compress input data that is 64 KB or more. If you try to compress less than that amount, the statistics report output for CSDFILEN indicates that 0 bytes of data have been compressed. If you try to decompress the data through CSDFILDE, the statistics report output for CSDFILDE indicates that 0 bytes have been expanded.