Transient-key cryptography: Difference between revisions

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'''Transient-key cryptography''' is a form of [[public-key cryptography]] wherein [[keypair]]s are generated and assigned to brief [[Interval (time)|intervals]] of time instead of to individuals or organizations, and the blocks of cryptographic data are chained through time. In a transient-key system, [[private key]]s are used briefly and then destroyed, which is why it is sometimes nicknamed “disposable crypto.” Data encrypted with a private key associated with a specific time interval can be irrefutably linked to that interval, making transient-key [[cryptography]] particularly useful for [[Trusted timestamping|digital trusted timestamping]]. Transient-key cryptography was invented in 1997 by Dr. Michael Doyle of [[Eolas]], and has been adopted in the [[ANSI ASC X9.95 Standard]] for [[Trusted timestamping|trusted timestamps]].

==Public-key vs. transient-key==

Both [[Public key|public- key]] and transient-key systems can be used to generate [[digital signature]]s that assert that a given piece of data has not changed since it was signed. But the similarities end there. In a traditional public key system, the public/private keypair is typically assigned to an individual, server, or [[organization]]. Data signed by a private key asserts that the signature came from the indicated source. Keypairs persist for years at a time, so the private component must be carefully guarded against disclosure; in a public-key system, anyone with access to a private key can counterfeit that person's digital signature.

In transient-key systems, however, the keypair is assigned to a brief interval of time, not to a particular person or entity. Data signed by a specific private key becomes associated with a specific time and date. A keypair is active only for a few minutes, after which the private key is permanently destroyed. Therefore, unlike public-key systems, transient-key systems do not depend upon the long-term security of the private keys.

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==Cross-verification==

[[Image:Cross-Certification.png|thumb|right|320px|A private key is cross-certified using two other transient-key servers.]]

Through independently operating servers, '''cross-certification''' can provide third-party proof of the validity of a time interval chain and irrefutable evidence of consensus on the current time. Transient-key cryptographic systems display high [[Byzantine fault tolerance]]. A web of interconnected cross-certifying servers in a distributed environment creates a widely witnessed chain of trust that is as strong as its strongest link. By contrast, entire [[Hierarchy|hierarchies]] of traditional public key systems can be compromised if a single private key is exposed.

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==Network archives==

Along with intervals, cross-certifications are stored in a network archive. Within a transient-key network, the [[archive]] is a logical [[database]] that can be stored and replicated on any system to enable verification of data that has been timestamped and signed by transient keys. A map of the set of accessible archives is stored within every digital signature created in the system. Whenever cross-certifications are completed at the beginning of an interval, the archive map is updated and published to all servers in the network.{{cn|date=April 2025}}

==Verification==

During an interval, the transient private key is used to sign data concatenated with trusted timestamps and authenticity certificates. To [[File verification|verify]] the data at a later time, a receiver accesses the [[Persistence (computer science)|persistent]] public key for the appropriate time interval. The public key applied to the digital signature can be passed through published cryptographic routines to unpack the [[Cryptographic hash function|hash]] of the original data, which is then compared against a fresh hash of the stored data to verify data integrity. If the signature successfully decrypts using a particular interval's published public key, the receiver can be assured that the signature originated during that time period. If the decrypted and fresh hashes match, the receiver can be assured that the data has not been tampered with since the transient private key created the timestamp and signed the data.

Transient-key cryptography was invented in 1997 by Dr. Michael D. Doyle of Eolas Technologies Inc., while working on the [[Visible Embryo Project]]<ref>{{cite patent |country=US |number=6381696 |title=Method and system for transient key digital time stamps |gdate=2002-04-30 |inventor=MD Doyle}}</ref><ref>{{cite patent |country=US |number=7047415 |title=System and method for widely witnessed proof of time |gdate=2006-05-16 |invent1=MD Doyle |invent2=PF Doyle |invent3=GW Bernsohn |invent4=JD Roberts }}</ref><ref>{{cite patent |country=US |number= 7210035 |title=System and method for graphical indicia for the certification of records |gdate=2007-04-24 |invent1=MD Doyle |invent2=RG Hamilton |invent3=MC Perrone |invent4=PF Doyle}}</ref> and later acquired by and productized by ProofSpace, Inc. It has been adopted as a national standard in the ANSI ASC X9.95 standard for Trusted Timestamping. Transient-key cryptography is the predecessor to [[Forward secrecy]] and formed the foundation of the forward-signature-chaining technology in the [[Bitcoin]] [[blockchain (database)|blockchain]] system.

==See also==

* [[Certificateless cryptography]]

* [[Certificate-based encryption]]

==References==

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[[Category:Blockchains]]

[[Category:Public-key cryptography]]

[[Category:Banking technology]]

[[Category:Public-key cryptography]]

[[Category:Data security]]