A signature scheme is provided in which a message is divided in to a first
portion which is hidden and is recovered during verification, and a
second portion which is visible and is required as input to the
verification algorithm. A first signature component is generated by
encrypting the first portion alone. An intermediate component is formed
by combining the first component and the visible portion and
cryptographically hashing them. A second signature component is then
formed using the intermediate component and the signature comprises the
first and second components with the visible portion. A verification of
the signature combines a first component derived only from the hidden
portion of the message with the visible portion and produces a hash of
the combination. The computed hash is used together with publicly
available information to generate a bit string corresponding to the
hidden portion. If the required redundancy is present the signature is
accepted and the message reconstructed from the recovered bit string and
the visible portion.