Cryptographic communications system and method
Signed document transmission system
Public key/signature cryptosystem with enhanced digital signature certification
Digital signature system and method based on a conventional encryption function
Public/key date-time notary facility
Digital document time-stamping with catenate certificate
Method for secure time-stamping of digital documents Patent #: 5136647
ApplicationNo. 992883 filed on 12/21/1992
US Classes:713/157, Chain or hierarchical certificates380/30, Public key713/177, Signature tree713/178Time stamp
ExaminersPrimary: Gregory, Bernarr E.
Attorney, Agent or Firm
International ClassesH04L 009/00
AbstractA cryptographic certificate attesting to the authenticity of original document elements, such as time of creation, content, or source, will lose its value when the cryptographic function underlying the certifying scheme is compromised. The present invention provides a means for extending the reliability of such a certificate by subjecting, prior to any such compromise, a combination of the original certificate and the document digital representation from which that certificate was derived to a scheme based on a different and ostensibly less vulnerable function. The new certificate resulting from this procedure extends the validity of the original authenticity by implacably incorporating the original certificate at a time when that certificate could only have been derived by legitimate means.