Guardtime IP Holdings Limited

Guardtime Sa

Märt Saarepera

Ahto Buldas

Andres Kroonmaa

Michael Gault

A client system is configured to obtain signatures for digital input records. An application program interface reformats each digital record, and this is used as an argument to a cryptographic hash function, from which a signature request is formed. The signature request is then submitted to a keyless, distributed hash tree infrastructure system, which returns a signature that includes recomputation values enabling recomputation from the result of the cryptographic hash function upward through the hash tree infrastructure to a root hash value at a calendar period corresponding to a time during which the signature request was originally submitted. An arbitrary subsequent test digital record is considered authenticated if, applying the cryptographic hash function to it, along with any other parameters included in the original computation, and recomputing an uppermost value using the recomputation values, the same composite calendar value is attained as when it was originally computed.

Document verification with distributed calendar infrastructure

Transformations of digital records are used as lowest level inputs to a tree data structure having a root in a core system and having nodes computed as digital combinations of child node values. Signature vectors are associated with the digital records and have parameters that enable recomputation upward through the tree data structure to either a current calendar value or onward to a composite calendar value that is a function of calendar values in a calendar, which comprises a set of computed calendar values, such that the calendar values have a time correspondence. Recomputation yields the same value only if a candidate digital record is an exact version of the original digital record included in the original computation of the value, indicating authentication of the candidate digital record. The authentication process as such is independent of any trust authority that issues cryptographic keys.

A method of generating a keyless digital multi-signature is provided. The method includes receiving multiple signature generation requests from one or more client computers, building subtrees based on the signature generation requests, and constructing a search tree including the subtrees. The method also includes assigning explicit length tags to leaf nodes of the search tree to balance the search tree and applying a hash function to each of the search tree nodes. The root hash value and the height of the search tree make up a generated aggregate signature request, followed by receiving an aggregate signature based on the aggregate signature request. The keyless digital multi-signature is generated based on the aggregate signature and contains an implicit length tag to verify that the number of signature generation requests is limited. The aggregate signature is generated if the height of the search tree does not exceed a predetermined height limitation.

System and method for generating keyless digital multi-signatures

Transformations of digital records are used as lowest level inputs to a tree data structure having a root in a core system and having nodes computed as digital combinations of child node values. A combination of root values is published in a permanent medium. Signature vectors are associated with the digital records and have parameters that enable recomputation upward through the tree data structure to either a current root value or to the published value. Recomputation yields the same value only if a candidate digital record is an exact version of the original digital record included in the original computation of the value.

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Tallinn, Estonia

Märt Saarepera