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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
==Public-key vs. transient-key
Both [[
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.
==Establishing data integrity
In a transient-key system, the source of time must be a consistent standard understood by all senders and receivers. Since a local [[system clock]] may be changed by a user, it is never used as a source of time. Instead, data is digitally signed with a time value derived from [[Universal Coordinated Time|Universal Coordinated Time (UTC)]] accurate to within a millisecond, in accordance with the [[ANSI ASC X9.95 Standard|ANSI ASC X9.95 standard for Trusted Timestamping]].{{citation needed|date=March 2024}} Whenever a time interval in a transient-key system expires, a new public/private keypair is generated, and the private key from the previous interval is used to digitally certify the new public key. The old private key is then destroyed. This "key-chaining" system is the immediate ancestor of the [[Blockchain]] technology in vogue today.
For the new interval, time values are obtained from a trusted third-party source, and specific moments in time can be [[interpolated]] in between received times by using a time-biasing method based on the internal system timer. If a trusted time source cannot be obtained or is not running within specified [[Engineering tolerance|tolerances]], transient private keys are not issued. In that case, the time interval chain is terminated, and a fresh one is begun. The old and new chains are connected through network archives, which enable all servers to continue to verify the [[data integrity]] through time of protected data, regardless of how often the chain must be restarted.
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==Cross-verification==
[[Image:Cross-Certification.png|
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.
An individual transient key interval chain can be cross-certified with other transient key chains and server instances. Through cross-certification, Server A signs Server B's interval chain, the signed data of which is the interval definition. In effect, the private keys from Server B are used to sign the public keys of Server A. In the diagram, a server instance is cross-certified with two other server instances (blue and orange). Cross-certification requires that the timestamp for the interval agree with the timestamp of the cross-certifying server within acceptable tolerances, which are user-defined and typically a few hundred milliseconds in duration.
==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
==See also==
* [[Certificateless cryptography]]
* [[Certificate-based encryption]]
==
{{reflist}}
[[Category:Blockchains]]▼
▲{{Cryptography navbox | public-key}}
[[Category:Banking technology]]▼
[[Category:Public-key cryptography]]
▲[[Category:Banking technology]]
[[Category:Data security]]
▲[[Category:Blockchains]]
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