1. A method for accessing a secured item including a header comprising a group of individually encrypted sub-headers and an encrypted data portion, comprising: selecting, by one or more computing devices, one of the individually encrypted sub-headers based on a correspondence of a user or group identifier associated with the sub-header to a user or to a group to which the user belongs; and accessing the sub-header, by the one or more computing devices, wherein the sub-header comprises access rules applicable to the user or to the group to which the user belongs for the secured item and a file key for accessing the encrypted data portion, wherein others of the individually encrypted sub-headers correspond to other users or groups and comprise access rules applicable to the other users or groups and the file key, and wherein the access rules for the sub-header are encrypted separate from the access rules of the others of the individually encrypted sub-headers.