US Patent Number 5956404
http://www.patents.ibm.com/details?pn=US05956404__
Schneier, Bruce
Kelsey, John
Abstract:
A method for digitally signing a message by a tamper-resistant device to
generate a digital signature. The method includes the step of hashing the
message to form message bits; and encrypting with a private key the
message bits, redundancy bits for the security of the signature, and
auditing bits to form the digital signature for the message. The auditing
bits provide an audit trail for the message. The auditing bits include one
or more of the following categories: signature-packet version bits to
identify the version of the device generating the signature; device ID
bits to identify the token generating the digital signature; key ID bits
to identify the private key; a packet-sequence number, which increments
every time the device generates a signature to indicate the sequence of
signatures generated; bits generated by hashing the prior signature to
provide an auditing trail of signatures generated and a time-stamp to
indicate the time when the signature is generated. The auditing bits may
further include a random number.
