Digital Preservation Coalition

Media and Formats - Compression and Encryption

File compression algorithms can substantially reduce file sizes and have been widely used in document or image transmission. Compression can either be lossless or lossy (with data loss but often higher levels of compression). Although appropriate in many cases for access and user copies, compression adds additional complexity to the preservation process and is normally not recommended for the storage of archival files.With current increases in storage capacity and reducing costs it is also less necessary. For some very large files e.g. digitised video, compressed formats may be the only viable option however for capture, storage and transmission.

In a similar way encryption is increasingly prevalent either to ensure that sensitive data is read only by the recipient or to ensure a digital product can only be used by an authorised user. Encryption also adds to the complexity of the preservation process and should be avoided if possible for archival copies.This may require strict implementation of physical and system security procedures for the archive of unencrypted files, or archival access to encryption keys.