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 one of the individually encrypted sub-headers based on the 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, wherein the sub-header comprises access rules applicable to the user or to the group to which the user belongs for the secured item, 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.