Systems and techniques relating to cryptographic keys include, in one implementation, a technique involving: generating a symmetric encryption key; and generating from the symmetric encryption key a family of symmetric encryption keys having a relationship such that a descendent key of the family is derivable from each key that is an ancestor of the descendent key in the family. Generating the family of symmetric encryption keys can involve cryptographically hashing the original symmetric encryption key and resulting hashed encryption keys. The technique can further include rolling over a key used in securing information by providing a next symmetric encryption key of the family in an order opposite that of an order of key generation; and a client can cryptographically hash a first symmetric encryption key to produce a second symmetric encryption key of the family and decrypt information associated with an electronic document with the key thus produced.