A new digital signature based only on a conventional encryption function (such as DES) is described which is as secure as the underlying encryption function -- the security does not depend on the difficulty of factoring and the high computational costs of modular arithmetic are avoided. The signature system can sign an unlimited number of messages, and the signature size increases logarithmically as a function of the number of messages signed. Signature size in a ‘typical’ system might range from a few hundred bytes to a few kilobytes, and generation of a signature might require a few hundred to a few thousand computations of the underlying conventional encryption function.
SyRA: Sybil-Resilient Anonymous Signatures with Applications to Decentralized Identity
We study Sybil-Resilient Anonymous (SyRA) signatures, a cryptographic primitive that enables credentialed users to generate, on demand, unlinkable pseudonyms tied to any given context, and issue signatures on behalf of these pseudonyms. Concretely, SyRA allows a distributed issuer to turn any legacy identity or personhood identifier, possibly of low entropy, into a unique associated cryptographic key of high pseudoentropy, for use in generating signatures for any given context. Sybil-resilient anonymous signatures achieve three main objectives: 1) Sybil resilience: every user is entitled to at most one digital identity, 2) anonymity: no information about the user’s real identity is leaked, and 3) non-interactive context switching: users can create on their own at most one credential for any given context in a manner that is unlinkable across contexts. We conceptualize the SyRA primitive as an ideal functionality in the Universal Composition (UC) setting and put forth SASSI, an efficient, pairing-based construction that realizes it by utilizing two levels of verifiable random functions (VRFs), a design which may be of independent interest. The first level consists of threshold VRF issuance of a user’s unique secret key tied to their real-world identifier. The second level allows a user to create signatures for each context, under a unique pseudonym per context. Compared to prior cryptographic tools capable of realizing SyRA, SASSI has the unique feature that issuers are stateless and hence do not need to retain any information about past user interactions, a relevant property for a decentralized implementation. We overview various applications of SASSI in multiparty systems, such as cryptocurrency account management and airdrops, e-voting (e.g., for decentralized governance), and privacy-preserving regulatory compliance (e.g., AML/CFT checks). In the context of creating addresses for digital assets, SyRA signatures enable users to embed their legacy identity into their address in a manner that protects their privacy for each application with which they interact. We demonstrate the practicality of SASSI by providing an implementation and performance evaluation of our construction.
the strongest encryption is just noise
Modern encryption standards really aren’t too bad to understand!
LEAF: Compact and Efficient Blind Signature from Code-based Assumptions
Recently, recent advancement in Asiacrypt'25, gives new blind signature frameworks, collectively named Tanuki(s), built upon cryptographic group actions. Their work introduces novel techniques and culminates in a concurrently secure blind signature framework. Straightforward instantiations based on CSIDH (CSI-FiSh) and LESS yield signature sizes of 4.5 KB and 64 KB respectively, providing the first efficient blind signatures in the isogeny-based and code-based literature allowing concurrent executions. In this work, we improve the code-based instantiations by using the canonical form of linear equivalent codes by a careful treatment. However, the canonical form does not naturally support a group action structure, which is central to the security proofs of Tanuki(s). Consequently and unfortunately, the original security guarantees do not directly apply. To address this, we develop two distinct non-black-box reductions for both blindness and the one-more unforgeability. In the end, the improvements do not compromise the security. This results in a concurrently secure code-based blind signature scheme with a compact signature size of 4.4 KB, which is approximately 1% smaller than the isogeny-based one. We also provide a C implementation where the signing time in 99ms and 268 Mcycles on an Intel i7 2.3~GHz CPU. We also look forward to our approaches benefiting advanced constructions built on top of LESS in the future.
Merkle Tree Certificates
This document describes Merkle Tree certificates, a new form of X.509 certificates which integrate public logging of the certificate, in the style of Certificate Transparency. The integrated design reduces logging overhead in the face of both shorter-lived certificates and large post-quantum signature algorithms, while still achieving comparable security properties to traditional X.509 and Certificate Transparency. Merkle Tree certificates additionally admit an optional signatureless optimization, which decreases the message size by avoiding signatures altogether, at the cost of only applying to up-to-date relying parties and older certificates.
HEIR: Homomorphic Encryption Intermediate Representation
HEIR is a compiler toolchain for fully homomorphic encryption (FHE). We aim to be the industry-standard compiler for FHE. Application developers, compiler engineers, hardware designers, and cryptography researchers can build upon HEIR to accelerate the research and development of production-strength privacy-first software systems.
Introducing Automatic Key Verification
Signal now offers a feature called “automatic key verification” which complements the existing safety number system. Signal is always end-to-end encrypted, and automatic key verification provides an additional, streamlined way to confirm that there’s no unexpected party between you and the other ...
Data Minimisation in Communication Protocols: A Formal Analysis...
With the growing amount of personal information exchanged over the Internet, privacy is becoming more and more a concern for users. One of the key principles in protecting privacy is data...
Automated Verification of Proofs in the Universal Composability Framework with Markov Decision Processes
Designing cryptographic protocols and proving these rigorously secure is an arduous and challenging task. Among the methods commonly used to prove security of cryptographic protocols, formalizing it in Canneti's Universal Composability (UC) Framework offers several benefits: (1) Modular design, (2) demonstrating that security remains under arbitrary composition and concurrent execution, (3) the security against any computationally polynomially bound adversary. However, working within the UC Framework can be cumbersome, requires a long time commitment by the prover, and it is prone to errors. While utilization of proof assistants in Cryptography and IT Security is a prominent research area, proof assistants for UC are still in their infancy. Here we show our ongoing work to utilize model checking for verification of proofs in the UC Framework, which to the best of our knowledge is the first attempt to do so. In this work we (1) formally create a Markov Decision Process (MDP) encoding a given proof in the UC Framework, (2) define and proof notions of soundness and completeness for the constructed MDP, (3) implement a proof of concept and (4) demonstrate practical feasibility through experimental evaluation. In summary, in this work we lay out the formal foundations for model checking UC proofs and create a tool that can not only be used for proof verification but also as an assistant for developing proofs in the UC Framework.
All elementary functions from a single operator
A single two-input gate suffices for all of Boolean logic in digital hardware. No comparable primitive has been known for continuous mathematics: computing elementary functions such as sin\sin, cos\cos, \sqrt{\phantom{x}}, and log\log has always required multiple distinct operations. Here we show that a single binary operator,
In Search of Hardness
Protocol studies, the next crypto cycle, and the next age of the world
A single signature by Trump can remove you from the internet
The Trump administration has likened them to the digital arm of al-Qaeda and, in an unprecedented move, just added them to the list of global terrorist organizations
Time-lock puzzle
A time-lock puzzle, or time-released cryptography, encrypts a message that cannot be decrypted until a specified amount of time has passed. The concept was first described by Timothy C. May,[1] and a solution first introduced by Ron Rivest, Adi Shamir, and David A. Wagner in 1996.[2] Time-lock puzzle are useful in cases where confidentiality of information is determined by time, such as a diarist who does not want their views released until 50 years after their death, an auction where bids are sealed until the bidding period is closed, electronic voting, and contract signing.[1][3] They can additionally be used in creating further cryptographic primitives, such as verifiable delay functions and zero knowledge proofs.[3]
zama-ai/concrete-ml
Concrete ML: Privacy Preserving ML framework using Fully Homomorphic Encryption (FHE), built on top of Concrete, with bindings to traditional ML frameworks.
Blink: Intent to Experiment: Signature-based Integrity
Blink: Intent to Experiment: Signature-based Integrity
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