This has applications in cloud computing to remove duplicate files from storage without the provider having access to the encryption keys.
[1] The combination of deduplication and convergent encryption was described in a backup system patent filed by Stac Electronics in 1995.
[2] This combination has been used by Farsite,[3] Permabit,[4] Freenet, MojoNation, GNUnet, flud, and the Tahoe Least-Authority File Store.
[7] This attack poses a problem for a user storing information that is non-unique, i.e. also either publicly available or already held by the adversary - for example: banned books or files that cause copyright infringement.
However, some implementations of convergent encryption where the plain-text is broken down into blocks based on file content, and each block then independently convergently encrypted may inadvertently defeat attempts at making the file unique by adding bytes at the beginning or end.