Patent ID: 7450717

Claim:
A method for encrypting information in a message that can be authenticated, the method comprising: adding a first authentication block to the information to be encrypted to form a concatenated field; logically subdividing the concatenated field into predetermined block lengths, including a residual field when the concatenated field is not sized as an even multiple of the predetermined block length; encrypting the subdivided fields using a first key to form cipher blocks; designating one of the cipher blocks as a designated cipher block, the other cipher blocks being nondesignated cipher blocks; subdividing the designated cipher block into a first cipher subblock and a second cipher subblock, such that a combined length of the second cipher subblock and the residual field and a second authentication block is the predetermined block length; encrypting the second cipher subblock and the residual portion together with the second authentication block using a second key to form a cipher residual block; and providing at least the first cipher subblock of the designated cipher block, the nondesignated cipher blocks and the cipher residual block as the message such that the message can be authenticated by decryption of a valid authentication block of either the first authentication block or the second authentication block.