The present invention relates generally to document identification over computer networks or other types of communication systems and, more particularly, to a scheme for multi-message multi-user signature aggregation.
In general, traditional cryptographic schemes providing encryption, key encapsulation, and signature services are expected to be replaced by quantum-resistant schemes in deployments during the next decade. The threat is so urgent that the US National Institute of Standards and Technology started a standardization competition in 2018 to select one or more so-called Post-Quantum (PQ) schemes. PQ signature schemes are expected to play a vital role in protecting the integrity of data in storage, during transmission, and even during computation.
While techniques such as multi-signatures are useful for compressing multiply signed individual transactions, the bulk of the transactions on Bitcoin™ and other networks are signed by different users. Therefore, new blocks are mostly made up of transactions with separate signatures that are not compressible by existing multi-signature schemes.
Moreover, prior schemes use traditional cryptographic primitives that assume hardness in the traditional non-quantum model. There is an urgent need for PQ signature schemes that allow aggregation.
Compression and aggregation of individual PQ signatures and of public keys remain a challenge.
The following presents a simplified summary of the innovation in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
In general, in one aspect, the invention features a method for signing and subsequently verifying a collection of digital messages including in at least one processor-based subsystem, selecting parameters that include two rings Ring1 and Ring2 and a module Mod, a ring homomorphism RHom from Ring1 to Ring2, a linear transformation THom from Ring2 to Mod, one or more range-defining bounds, and one or more formatted hash functions, for each User_i selecting a private key PrivKey_i that includes an element f_i in the Ring1 satisfying a first set of predetermined conditions and selecting an associated public key PubKey_i that includes the value Rhom(f_i), for each User_i selecting a digital document Doc_i and an element Rand_i in Ring1 satisfying a second set of predetermined conditions, and computing a signature Sig_i that includes elements C_i and Z_i in Ring1, wherein C_i is the output of a function whose input includes one or more quantities derived from THom(RHom(Rand_i)), Doc_i, and PubKey_i, and wherein the element Z_i is the output of a function whose input includes PrivKey_i, Rand_i, and C_i, and wherein Z_i satisfies a third set of predetermined conditions, aggregating a collection of signatures Sig_1, . . . , Sig_K on documents Doc_1, . . . , Doc_K to form an aggregate signature AggSig that includes quantities Z, Y, Y_1, . . . , Y_K, wherein the element Y is in Ring2 and is computed as the output of a function whose input includes RHom(Rand_1), . . . , RHom(Rand_K), wherein the elements Y_1, . . . , Y_K are in Mod and wherein each Y_i is computed as the output of a function whose input includes THom(RHom(Rand_i)), and wherein the element Z is in Ring1 and is computed as the output of a function whose input includes C_1, . . . , C_K and Z_1, . . . , Z_K, and verifying the validity of the aggregate signature AggSig on the documents Doc_1, . . . , Doc_K for the public keys PubKey_1, . . . , PubKey_K by a process that includes verifying that the quantities Z, Y, Y_1, . . . , Y_K satisfy a fourth set of predetermined conditions.
These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where:
The subject innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention.
Post-Quantum (PQ) signature schemes are known for large key and signature sizes, which may inhibit their deployment in real world applications. The present invention is a PQ signature scheme MMSAT that is a scheme capable of aggregating and compressing unrelated messages signed individually by different parties. The present invention extends the notion of multi-signatures, which are signatures that support aggregation of signatures on a single message signed by multiple parties. Multi-signatures are especially useful in Blockchain applications, where a transaction may be signed by multiple users. The present invention achieves significant gains in bandwidth and storage requirements by allowing aggregation and compression of multi-key and multi-message transactions. The present invention is derived by extending the PASSRS scheme, so the security of the scheme relies on the hardness of the Vandermonde-SIS problem. When aggregated and compressed, a signature includes two parts. The first part is a post-quantum size signature that grows very slowly, scaling by on the order of log K bits for K signatures. The second part scales linearly with K, but bears only a short fixed cost of 2λ bits per signature, where λ represents the security parameter. Even for a modest number of signatures, the overhead of MMSAT is in line with that of traditional signature schemes such as the Elliptic Curve Digital Signature Algorithm (ECDSA). The present invention additionally includes a variant MMSATK of MMSAT that is capable of aggregating and compressing the public keys used by different parties.
Referring now to
The subsystem 155 in this illustrative embodiment can have a similar configuration to that of subsystem 105. The processor 160 has associated input/output circuitry 164, memories 168, clock and timing circuitry 173, and a display 176. Inputs include a touchscreen/keyboard 155. Communication of subsystem 155 with the outside world is via transceiver 162.
The present invention is a PQ signature scheme, referred to herein as “MMSAT,” which supports aggregation across unrelated signatures signed by different users. An aggregated MMSAT signature has size roughly equal to a single PQ signature plus 2λ-bits per signature aggregated. From a practical perspective, even for a modest number of signatures (e.g., a few hundred), the aggregate signature size of MMSAT represents an improvement over traditional signature schemes such as elliptic curve-based signatures (ECDSA), e.g. it is 19-times smaller than Bimodal Lattice Signature Scheme (BLISS) and 1.9 times smaller than ECDSA for 1000 signatures at 128-bit security.
The present invention uses an ∞-norm analysis to give improved estimates for the forgery probability from lattice reduction, leading to optimized parameters.
The present invention is a method and system for multiple users to sign multiple documents, for those signatures to be aggregated and compressed based on ring homomorphisms and linear transformations, and for the users' public keys to be aggregated and compressed based on ring homomorphisms and linear transformations. The ring homomorphism may utilize two rings Ring1 and Ring2 and a module Mod, a ring homomorphism RHom: Ring1-->Ring2, and a linear transformation THom: Ring2-->Mod. The private keys can include elements f lying in a specified subset of Ring1, the public keys can include the value RHom(f) in Ring2, the individual signatures in accordance with the invention may include quantities computed from the individual documents and individual private and public keys via specified formatted hash functions and algebraic operations in the ring Ring1 and applications of the maps RHom and THom, and the aggregated and compressed signature on the collection of documents may include quantities computed from the individual signatures, the individual documents, and the individual public keys via specified formatted hash functions and algebraic operations in the rings Ring1 and Ring2 and applications of the maps RHom and THom.
Table 1, shown below, lists public parameters used variously by PASSRS and MMSAT and MMSATK.
≥
used for compression
→
(de)
→ {−1, 1}
→ {subsets of Ω containing
indicates data missing or illegible when filed
In Table 2, an exemplary sign algorithm for individual signatures is shown.
In Table 3, an exemplary verification algorithm for individual signatures is shown.
In Table 4, an exemplary MMSAT aggregate signature algorithm is shown.
|Ω, zi, μi,
|Ω)iϵ[K]
|Ω)
|Ω + ... + βK
|Ω
|Ω))iϵ[K], result
In Table 5, an exemplary MMSAT verify aggregate signature algorithm is shown.
In Table 6, an exemplary MMSAT sign algorithm with public key compression is illustrated.
|Ω, zi, μi,
|Ω)iϵ[K]
|Ω)
|Ω)
|Ω + ... + βK
|Ω
|Ω′
|Ω′
In Table 7, an exemplary MMSAT verify individual signature with compressed public key algorithm is shown.
It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be within the scope of the present invention except as limited by the scope of the appended claims.
This application claims the benefit of U.S. Ser. No. 62/900,246, filed Sep. 13, 2019, and U.S. Ser. No. 63/015,212, filed Apr. 24, 2019.
This invention was made with government support under Grant No. CNS-1561709 and Grant No. CNS-1561536 awarded by the National Science Foundation. The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US20/50378 | 9/11/2020 | WO |
Number | Date | Country | |
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62900246 | Sep 2019 | US | |
63015212 | Apr 2020 | US |