US Patent 9350549 Selective shredding in a deduplication system

Making a target file impractical to be retrieved comprises decrypting a directory manager file using a first directory manager file key. The directory manager file includes an encryption key for a segment that is used when reconstructing a target file. The directory manager file is modified by deleting a reference to the target file. The reference includes a file encryption key. Retrieving the target file is made impractical by the deletion of the reference to the target file in the directory manager file. The modified directory manager file is encrypted using a second directory manager file key.