Hierarchical attribute-based encryption and decryption

A method of generating a user secret key for use in a hierarchical attribute-based cryptographic system comprising a hierarchy of domain authorities and a plurality of attributes assignable to a user, the method comprising:

• generating a domain secret key for a domain authority in the hierarchy based on
• a) a domain secret key of a parent domain authority of the domain authority in the hierarchy or
• b) a root secret key of a root authority of the hierarchy of domain authorities generating a user secret key for the user based on the domain secret key and one or more attribute representations comprising public key information representing a set of the attributes assigned to the user.
• wherein the attribute representations are independent of the hierarchy of domain authorities.

A method of decrypting a ciphertext for use in a hierarchical attribute-based cryptographic system comprising a hierarchy of domain authorities and a plurality of attributes assignable to a user, the method comprising:

• receiving a ciphertext associated with a policy over a plurality of attributes, wherein the ciphertext is further associated with at least part of::--the hierarchy of domain authorities by encryption based on public key information associated with the at least part of the hierarchy;
• and
• decrypting the ciphertext based on a user secret key issued for a user by a domain authority of said at least part of the hierarchy of domain authorities, wherein the user secret key comprises a first component representing a position in the hierarchy and a second component representing a set of attributes assigned to the user, the first component being based on a portion of a public key associated with at least part of the hierarchy of domain authorities and the second component being based on attribute representations comprising public key information representing the set of the attributes assigned to the user,
• wherein the attribute representations are independent of the hierarchy of domain authorities and
• wherein the decrypting of the ciphertext is enabled only if the set of attributes corresponding to the user secret key satisfies the policy of the ciphertext.