Publicly auditable conditional blind signatures

2021 ◽  
Vol 29 (2) ◽  
pp. 229-271
Author(s):  
Panagiotis Grontas ◽  
Aris Pagourtzis ◽  
Alexandros Zacharakis ◽  
Bingsheng Zhang
Keyword(s):  
Proof Of Concept ◽  
Equivalence Test ◽  
Zero Knowledge ◽  
Private Key ◽  
Blind Signatures ◽  
Cryptographic Primitive ◽  
Security Properties ◽  
Designated Verifier

This work formalizes Publicly Auditable Conditional Blind Signatures (PACBS), a new cryptographic primitive that allows the verifiable issuance of blind signatures, the validity of which is contingent upon a predicate and decided by a designated verifier. In particular, when a user requests the signing of a message, blinded to protect her privacy, the signer embeds data in the signature that makes it valid if and only if a condition holds. A verifier, identified by a private key, can check the signature and learn the value of the predicate. Auditability mechanisms in the form of non-interactive zero-knowledge proofs are provided, so that a cheating signer cannot issue arbitrary signatures and a cheating verifier cannot ignore the embedded condition. The security properties of this new primitive are defined using cryptographic games. A proof-of-concept construction, based on the Okamoto–Schnorr blind signatures infused with a plaintext equivalence test is presented and its security is analyzed.

Biometric Identity Based Encryption

2011 ◽  
pp. 181-193
Author(s):  
Neyire Deniz Sarier
Keyword(s):  
New Method ◽  
Future Trends ◽  
Computational Power ◽  
Collusion Attacks ◽  
Implementation Challenges ◽  
Identity Based Encryption ◽  
Cryptographic Primitive ◽  
Attack Scenario ◽  
Security Properties ◽  
Identity Based

In this chapter, we evaluate the security properties and different applications of Identity Based Encryption (IBE) systems. Particularly, we consider biometric identities for IBE, which is a new encryption system defined as fuzzy IBE. Next, we analyze the security aspects of fuzzy IBE in terms of the security notions it must achieve and the prevention of collusion attacks, which is an attack scenario specific to fuzzy IBE. In this context, we present a new method that avoids the collusion attacks and describe the currently most efficient biometric IBE scheme that implements this new method. Also, we investigate implementation challenges for biometric IBE systems, where fuzzy IBE could be a potential cryptographic primitive for biometric smartcards. Due to the limited computational power of these devices, a different solution for biometric IBE is considered, which is the encryption analogue of the biometric identity based signature system of Burnett et al. (2007). Finally, we state the future trends for biometric IBE systems and conclude our results.

scholarly journals Dynamic Public Key Certificates with Forward Secrecy

Electronics ◽  
2021 ◽  
Vol 10 (16) ◽  
pp. 2009
Author(s):  
Hung-Yu Chien
Keyword(s):  
Public Key Infrastructure ◽  
Public Key ◽  
Practical Reasons ◽  
Forward Secrecy ◽  
The Public ◽  
Private Key ◽  
Security Properties ◽  
The Subject ◽  
Key Exposure ◽  
Chameleon Hash

Conventionally, public key certificates bind one subject with one static public key so that the subject can facilitate the services of the public key infrastructure (PKI). In PKI, certificates need to be renewed (or revoked) for several practical reasons, including certificate expiration, private key breaches, condition changes, and possible risk reduction. The certificate renewal process is very costly, especially for those environments where online authorities are not available or the connection is not reliable. A dynamic public key certificate (DPKC) facilitates the dynamic changeover of the current public–private key pairs without renewing the certificate authority (CA). This paper extends the previous study in several aspects: (1) we formally define the DPKC; (2) we formally define the security properties; (3) we propose another implementation of the Krawczyk–Rabin chameleon-hash-based DPKC; (4) we propose two variants of DPKC, using the Ateniese–Medeiros key-exposure-free chameleon hash; (5) we detail two application scenarios.

scholarly journals Functional Encryption for Pattern Matching with a Hidden String

Cryptography ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Jongkil Kim ◽  
Yang-Wai Chow ◽  
Willy Susilo ◽  
Joonsang Baek ◽  
Intae Kim
Keyword(s):  
Access Control ◽  
Pattern Matching ◽  
Public Information ◽  
Functional Encryption ◽  
Fine Grained ◽  
Private Key ◽  
Diffie Hellman ◽  
Data Owner ◽  
Security Properties

We propose a new functional encryption for pattern matching scheme with a hidden string. In functional encryption for pattern matching (FEPM), access to a message is controlled by its description and a private key that is used to evaluate the description for decryption. In particular, the description with which the ciphertext is associated is an arbitrary string w and the ciphertext can only be decrypted if its description matches the predicate of a private key which is also a string. Therefore, it provides fine-grained access control through pattern matching alone. Unlike related schemes in the literature, our scheme hides the description that the ciphertext is associated with. In many practical scenarios, the description of the ciphertext cannot be public information as an attacker may abuse the message description to identify the data owner or classify the target ciphertext before decrypting it. Moreover, some data owners may not agree to reveal any ciphertext information since it simply gives greater advantage to the adversary. In this paper, we introduce the first FEPM scheme with a hidden string, such that the adversary cannot get any information about the ciphertext from its description. The security of our scheme is formally analyzed. The proposed scheme provides both confidentiality and anonymity while maintaining its expressiveness. We prove these security properties under the interactive general Diffie–Hellman assumption (i-GDH) and a static assumption introduced in this paper.

scholarly journals Return of the Hidden Number Problem.

2018 ◽  
pp. 146-168 ◽  
Author(s):  
Keegan Ryan
Keyword(s):  
Side Channel ◽  
Proof Of Concept ◽  
Private Key ◽  
Side Channels ◽  
Signature Generation ◽  
Number Problem ◽  
Minimum Number ◽  
Hidden Number Problem ◽  
State Changes ◽  
Full Proof

Side channels have long been recognized as a threat to the security of cryptographic applications. Implementations can unintentionally leak secret information through many channels, such as microarchitectural state changes in processors, changes in power consumption, or electromagnetic radiation. As a result of these threats, many implementations have been hardened to defend against these attacks. Despite these mitigations, this work presents a novel side-channel attack against ECDSA and DSA. The attack targets a common implementation pattern that is found in many cryptographic libraries. In fact, about half of the libraries that were tested exhibited the vulnerable pattern. This pattern is exploited in a full proof of concept attack against OpenSSL, demonstrating that it is possible to extract a 256-bit ECDSA private key using a simple cache attack after observing only a few thousand signatures. The target of this attack is a previously unexplored part of (EC)DSA signature generation, which explains why mitigations are lacking and the issue is so widespread. Finally, estimates are provided for the minimum number of signatures needed to perform the attack, and countermeasures are suggested to protect against this attack.

A New Code-Based Blind Signature Scheme

2021 ◽  
Author(s):  
Siyuan Chen ◽  
Peng Zeng ◽  
Kim-Kwang Raymond Choo
Keyword(s):  
Coding Theory ◽  
Blind Signature ◽  
Quantum Computers ◽  
Security Level ◽  
Zero Knowledge ◽  
Syndrome Decoding ◽  
Cryptographic Primitive ◽  
Hard Problems ◽  
Np Complete ◽  
Level 2

Abstract Blind signature is an important cryptographic primitive with widespread applications in secure e-commerce, for example to guarantee participants’ anonymity. Existing blind signature schemes are mostly based on number-theoretic hard problems, which have been shown to be solvable with quantum computers. The National Institute of Standards and Technology (NIST) began in 2017 to specify a new standard for digital signatures by selecting one or more additional signature algorithms, designed to be secure against attacks carried out using quantum computers. However, none of the third-round candidate algorithms are code-based, despite the potential of code-based signature algorithms in resisting quantum computing attacks. In this paper, we construct a new code-based blind signature (CBBS) scheme as an alternative to traditional number-theoretic based schemes. Specifically, we first extend Santoso and Yamaguchi’s three pass identification scheme to a concatenated version (abbreviated as the CSY scheme). Then, we construct our CBBS scheme from the CSY scheme. The security of our CBBS scheme relies on hardness of the syndrome decoding problem in coding theory, which has been shown to be NP-complete and secure against quantum attacks. Unlike Blazy et al.’s CBBS scheme which is based on a zero-knowledge protocol with cheating probability $2/3$, our CBBS scheme is based on a zero-knowledge protocol with cheating probability $1/2$. The lower cheating probability would reduce the interaction rounds under the same security level and thus leads to a higher efficiency. For example, to achieve security level $2^{-82}$, the signature size in our CBBS scheme is $1.63$ MB compared to $3.1$ MB in Blazy et al.’s scheme.

scholarly journals Attack on Kayawood protocol: uncloaking private keys

2020 ◽  
Vol 15 (1) ◽  
pp. 237-249
Author(s):  
Matvei Kotov ◽  
Anton Menshov ◽  
Alexander Ushakov
Keyword(s):  
Heuristic Algorithm ◽  
Braid Group ◽  
Key Agreement ◽  
Private Key ◽  
The Core ◽  
Key Agreement Protocol ◽  
Finite Set ◽  
Security Properties ◽  
The Right ◽  
Parameter Values

AbstractWe analyze security properties of a two-party key-agreement protocol recently proposed by I. Anshel, D. Atkins, D. Goldfeld, and P. Gunnels, called Kayawood protocol. At the core of the protocol is an action (called E-multiplication) of a braid group on some finite set. The protocol assigns a secret element of a braid group to each party (private key). To disguise those elements, the protocol uses a so-called cloaking method that multiplies private keys on the left and on the right by specially designed elements (stabilizers for E-multiplication).We present a heuristic algorithm that allows a passive eavesdropper to recover Alice’s private key by removing cloaking elements. Our attack has 100% success rate on randomly generated instances of the protocol for the originally proposed parameter values and for recent proposals that suggest to insert many cloaking elements at random positions of the private key. Implementation of the attack is available on GitHub.

scholarly journals ZPiE: Zero-Knowledge Proofs in Embedded Systems

Mathematics ◽  
2021 ◽  
Vol 9 (20) ◽  
pp. 2569
Author(s):  
Xavier Salleras ◽  
Vanesa Daza
Keyword(s):  
Embedded Systems ◽  
Identity Management ◽  
State Of The Art ◽  
Limited Resources ◽  
Proof Of Concept ◽  
Authentication Protocols ◽  
Cryptographic Primitives ◽  
Zero Knowledge ◽  
In The Wild ◽  
The Internet Of Things

Zero-Knowledge Proofs (ZKPs) are cryptographic primitives allowing a party to prove to another party that the former knows some information while keeping it secret. Such a premise can lead to the development of numerous privacy-preserving protocols in different scenarios, like proving knowledge of some credentials to a server without leaking the identity of the user. Even when the applications of ZKPs were endless, they were not exploited in the wild for a couple of decades due to the fact that computing and verifying proofs was too computationally expensive. However, the advent of efficient schemes (in particular, zk-SNARKs) made this primitive to break into the scene in fields like cryptocurrencies, smart-contracts, and more recently, self-sovereign scenarios: private-by-design identity management and authentication. Nevertheless, its adoption in environments like the Internet of Things (IoT) remains unexplored due to the computational limitations of embedded systems. In this paper, we introduce ZPiE, a C library intended to create ZKP applications to be executed in embedded systems. Its main feature is portability: it can be compiled, executed, and used out-of-the-box in a wide variety of devices. Moreover, our proof-of-concept has been proved to work smoothly in different devices with limited resources, which can execute state-of-the-art ZKP authentication protocols.

Theory and Practice of Secure E-Voting Systems

2013 ◽  
pp. 428-459
Author(s):  
Kun Peng
Keyword(s):  
Linear Algebra ◽  
Theory And Practice ◽  
Encryption Algorithm ◽  
Electronic Voting ◽  
Zero Knowledge ◽  
Validity Check ◽  
Elgamal Encryption ◽  
Security Properties ◽  
Proof Techniques ◽  
Zero Knowledge Proof

Electronic voting is a popular application of cryptographic and network techniques to e-government. Most of the existing e-voting schemes can be classified into two categories: homomorphic voting and shuffling-based voting. In a homomorphic voting, an encryption algorithm with special homomorphic property (e.g. ElGamal encryption or Paillier encryption) is employed to encrypt the votes such that the sum of the votes can be recovered without decrypting any single vote. An advantage of homomorphic voting is efficient tallying. Tallying in homomorphic voting only costs one single decryption operation for each candidate. In this chapter, the existing e-voting solutions in both categories are surveyed and analysed. The key security properties in both categories are presented and then the existing e-voting schemes in each category are checked against the corresponding security properties. Security and efficiency of the schemes are analysed and the strongest security and highest efficiency achievable in each category is estimated. Problems and concerns about the existing solutions including vulnerability to malicious voters and (or) talliers, possible failure of complete correctness, imperfect privacy, dependence on computational assumptions, and exaggerated efficiency are addressed. New approaches will be proposed in both kinds of solutions to overcome the existing drawbacks in them. In homomorphic e-voting, the authors deal with possibly malicious voters and aim at efficient vote validity check to achieve strong and formally provable soundness and privacy. It can be implemented through new zero knowledge proof techniques, which are both efficient and provably secure. In mix-network-based e-voting, the authors deal with possibly deviating operations of both voters and talliers and aim at efficient proof of validity of shuffling, which guarantees the desired security properties and prevent attacks from malicious participants. It can be based on inspiring linear algebra knowledge and the new zero knowledge proof of existence of secret permutation.

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