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Undeniable Signature
An undeniable signature is a digital signature scheme which allows the signer to be selective to whom they allow to verify signatures. The scheme adds explicit signature repudiation, preventing a signer later refusing to verify a signature by omission; a situation that would devalue the signature in the eyes of the verifier. It was invented by David Chaum and Hans van Antwerpen in 1989. Overview In this scheme, a signer possessing a private key can publish a signature of a message. However, the signature reveals nothing to a recipient/verifier of the message and signature without taking part in either of two interactive protocols: * Confirmation protocol, which confirms that a candidate is a valid signature of the message issued by the signer, identified by the public key. * Disavowal protocol, which confirms that a candidate is not a valid signature of the message issued by the signer. The motivation for the scheme is to allow the signer to choose to whom signatures are verified. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Signature
A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created by a known sender (authenticity), and that the message was not altered in transit (integrity). Digital signatures are a standard element of most cryptographic protocol suites, and are commonly used for software distribution, financial transactions, contract management software, and in other cases where it is important to detect forgery or tampering. Digital signatures are often used to implement electronic signatures, which includes any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
David Chaum
David Lee Chaum (born 1955) is an American computer scientist, cryptographer, and inventor. He is known as a pioneer in cryptography and privacy-preserving technologies, and widely recognized as the inventor of digital cash. His 1982 dissertation "Computer Systems Established, Maintained, and Trusted by Mutually Suspicious Groups" is the first known proposal for a blockchain protocol. Complete with the code to implement the protocol, Chaum's dissertation proposed all but one element of the blockchain later detailed in the Bitcoin whitepaper. He has been referred to as "the father of online anonymity", and "the godfather of cryptocurrency". He is also known for developing ecash, an electronic cash application that aims to preserve a user's anonymity, and inventing many cryptographic protocols like the blind signature, mix networks and the Dining cryptographers protocol. In 1995 his company DigiCash created the first digital currency with eCash.Greenberg, Andy (2012). ''This M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plausible Deniability
Plausible deniability is the ability of people, typically senior officials in a formal or informal chain of command, to denial, deny knowledge of or responsibility for any damnable actions committed by members of their organizational hierarchy. They may do so because of a lack or absence of evidence that can confirm their participation, even if they were personally involved in or at least willful blindness, willfully ignorant of the actions. If illegal or otherwise disreputable and unpopular activities become public, high-ranking officials may deny any awareness of such acts to insulate themselves and Blame#Blame shifting, shift the blame onto the agents who carried out the acts, as they are confident that their doubters will be unable to prove otherwise. The lack of evidence to the contrary ostensibly makes the denial plausible (credible), but sometimes, it makes any accusations only cause of action, unactionable. The term typically implies forethought, such as intentionally setti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Designated Verifier Signature
A designated verifier signature is a signature scheme in which signatures can only be verified by a single, designated verifier, designated as part of the signature creation. Designated verifier signatures were first proposed in 1996 by Jakobsson Markus, Kazue Sako, and Russell Impagliazzo. Proposed as a way to combine authentication and off-the-record messages, designated verifier signatures allow authenticated, private conversations to take place. Unlike in undeniable signature scheme the protocol of verifying is non-interactive; i.e., the signer chooses the designated verifier (or the set of designated verifiers) in advance and does not take part in the verification process. See also * Non-repudiation * Undeniable signature An undeniable signature is a digital signature scheme which allows the signer to be selective to whom they allow to verify signatures. The scheme adds explicit signature repudiation, preventing a signer later refusing to verify a signature by omissi ... Re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discrete Logarithm Problem
In mathematics, for given real numbers ''a'' and ''b'', the logarithm log''b'' ''a'' is a number ''x'' such that . Analogously, in any group ''G'', powers ''b''''k'' can be defined for all integers ''k'', and the discrete logarithm log''b'' ''a'' is an integer ''k'' such that . In number theory, the more commonly used term is index: we can write ''x'' = ind''r'' ''a'' (mod ''m'') (read "the index of ''a'' to the base ''r'' modulo ''m''") for ''r''''x'' ≡ ''a'' (mod ''m'') if ''r'' is a primitive root of ''m'' and gcd(''a'',''m'') = 1. Discrete logarithms are quickly computable in a few special cases. However, no efficient method is known for computing them in general. Several important algorithms in public-key cryptography, such as ElGamal base their security on the assumption that the discrete logarithm problem over carefully chosen groups has no efficient solution. Definition Let ''G'' be any group. Denote its group operation by mult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prime Number
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, or , involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order. The property of being prime is called primality. A simple but slow method of checking the primality of a given number n, called trial division, tests whether n is a multiple of any integer between 2 and \sqrt. Faster algorithms include the Miller–Rabin primality test, which is fast but has a small chance of error, and the AKS primality test, which always pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Element (finite Field)
In field theory, a primitive element of a finite field is a generator of the multiplicative group of the field. In other words, is called a primitive element if it is a primitive th root of unity in ; this means that each non-zero element of can be written as for some integer . If is a prime number, the elements of can be identified with the integers modulo . In this case, a primitive element is also called a primitive root modulo . For example, 2 is a primitive element of the field and , but not of since it generates the cyclic subgroup of order 3; however, 3 is a primitive element of . The minimal polynomial of a primitive element is a primitive polynomial. Properties Number of primitive elements The number of primitive elements in a finite field is , where is Euler's totient function, which counts the number of elements less than or equal to which are relatively prime to . This can be proved by using the theorem that the multiplicative group of a finite fie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Non-repudiation
Non-repudiation refers to a situation where a statement's author cannot successfully dispute its authorship or the validity of an associated contract. The term is often seen in a legal setting when the authenticity of a signature is being challenged. In such an instance, the authenticity is being "repudiated". For example, Mallory buys a cell phone for $100, writes a paper cheque as payment, and signs the cheque with a pen. Later, she finds that she can't afford it, and claims that the cheque is a forgery. The signature guarantees that only Mallory could have signed the cheque, and so Mallory's bank must pay the cheque. This is non-repudiation; Mallory cannot repudiate the cheque. In practice, pen-and-paper signatures aren't hard to forge, but digital signatures can be very hard to break. In security In general, ''non-repudiation'' involves associating actions or changes with a unique individual. For example, a secure area may use a key card access system where non-repudiation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Designated Verifier Signature
A designated verifier signature is a signature scheme in which signatures can only be verified by a single, designated verifier, designated as part of the signature creation. Designated verifier signatures were first proposed in 1996 by Jakobsson Markus, Kazue Sako, and Russell Impagliazzo. Proposed as a way to combine authentication and off-the-record messages, designated verifier signatures allow authenticated, private conversations to take place. Unlike in undeniable signature scheme the protocol of verifying is non-interactive; i.e., the signer chooses the designated verifier (or the set of designated verifiers) in advance and does not take part in the verification process. See also * Non-repudiation * Undeniable signature An undeniable signature is a digital signature scheme which allows the signer to be selective to whom they allow to verify signatures. The scheme adds explicit signature repudiation, preventing a signer later refusing to verify a signature by omissi ... Re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Topics In Cryptography
The following outline is provided as an overview of and topical guide to cryptography: Cryptography (or cryptology) – practice and study of hiding information. Modern cryptography intersects the disciplines of mathematics, computer science, and engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce. Essence of cryptography * Cryptographer * Encryption/decryption * Cryptographic key * Cipher * Ciphertext * Plaintext * Code * Tabula recta * Alice and Bob Uses of cryptographic techniques * Commitment schemes * Secure multiparty computation * Electronic voting * Authentication * Digital signatures * Crypto systems * Dining cryptographers problem * Anonymous remailer * Pseudonymity * Onion routing * Digital currency * Secret sharing * Indistinguishability obfuscation Branches of cryptography * Multivariate cryptography * Post-quantum cryptography * Quantum cryptography * Steganography * Visual cryptography History ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryptography
Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others. Core concepts related to information security ( data confidentiality, data integrity, authentication, and non-repudiation) are also central to cryptography. Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications. Cryptography prior to the modern age was effectively synonymo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
