Methods are provided for encoding and decoding a digital message between a sender and a recipient in a system including a plurality of private key generators ("PKGs"). The PKGs include at least a root PKG and n lower-level PKG in the hierarchy between the root PKG and the recipient. A root key generation secret is selected and is known only to the root PKG. A root key generation parameter is generated based on the root key generation secret. A lower-level key generation secret is selected for each of the n lower-level PKGs, wherein each lower-level key generation secret is known only to its associated lower-level PKG. A lower-level key generation parameter also is generated for each of the n lower-level PKGs using at least the lower-level key generation secret for its associated lower-level private key generator. The message is encoded to form a ciphertext using at least the root key generation parameter and recipient identity information associated with the recipient. A recipient private key is generated such that the recipient private key is related to at least the root key generation secret, one or more of the n lower-level key generation secrets, and the recipient identity information. The ciphertext is decoded to recover the message using at least the recipient private key.