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In cryptography, an adversary (rarely opponent, enemy) is a malicious entity whose aim is to prevent the users of the cryptosystem from achieving their goal (primarily privacy, integrity, and availability of data).
Cryptography or cryptology (from "hidden, secret"; and graphein, "to write", or -logia, "study", respectively ) is the practice and study of techniques for secure communication in the presence of third parties called adversaries.

Security parameter

The advantage is specified as a function of the security parameter.
Both the resource requirements of the cryptographic algorithm or protocol as well as the adversary's probability of breaking security are expressed in terms of the security parameter.

Computationally bounded adversary

computational boundednesscomputationally bounded
computationally bounded or unbounded (i.e. in terms of time and storage resources),
In the computationally bounded adversary model the channel – the adversary – is restricted to only being able to perform a reasonable amount of computation to decide which bits of the code word need to change.


cryptosystemscryptographic systemcrypto system
In cryptography, an adversary (rarely opponent, enemy) is a malicious entity whose aim is to prevent the users of the cryptosystem from achieving their goal (primarily privacy, integrity, and availability of data).

Spoofing attack

An adversary's efforts might take the form of attempting to discover secret data, corrupting some of the data in the system, spoofing the identity of a message sender or receiver, or forcing system downtime.

Computer security

cybersecuritysecuritycyber security
Not surprisingly, the former term predominates in the cryptographic and the latter in the computer security literature.

Alice and Bob

Eve, Mallory, Oscar and Trudy are all adversarial characters widely used in both types of texts.

Network security

mobile or non-mobile (e.g. in the context of network security)

Provable security

provably secureproven securesecurity reduction
In such a proof, the capabilities of the attacker are defined by an adversarial model (also referred to as attacker model): the aim of the proof is to show that the attacker must solve the underlying hard problem in order to break the security of the modelled system.

Replay attack

replay attacksFreshnessreplay
This is carried out either by the originator or by an adversary who intercepts the data and re-transmits it, possibly as part of a masquerade attack by IP packet substitution.

Noisy-storage model

It assumes that the quantum memory device of an attacker (adversary) trying to break the protocol is imperfect (noisy).

Secure multi-party computation

secure multiparty computationsecure computationmulti-party computing
Unlike traditional cryptographic tasks, where cryptography assures security and integrity of communication or storage and the adversary is outside the system of participants (an eavesdropper on the sender and receiver), the adversary in this model controls actual participants.

Disk encryption theory

XTSLRWdisk encryption
The first property requires defining an adversary from whom the data is being kept confidential.

Information-theoretic security

information-theoretically secureinformation theoretic securityperfect secrecy
Information-theoretic security is a cryptosystem whose security derives purely from information theory, so that the system cannot be broken even if the adversary has unlimited computing power.

Standard model (cryptography)

standard modelstandard model of cryptography
In cryptography the standard model is the model of computation in which the adversary is only limited by the amount of time and computational power available.

Advantage (cryptography)

Note that in this context, the "adversary" is itself an algorithm and not a person.

Chosen-plaintext attack

chosen plaintextchosen plaintext attackchosen plaintexts
In a chosen-plaintext attack the adversary can (possibly adaptively) ask for the ciphertexts of arbitrary plaintext messages.

Cryptographic hash function

cryptographic hashhashhashing
Informally, these properties mean that a malicious adversary cannot replace or modify the input data without changing its digest.

Integrated Encryption Scheme

Integrated Encryption Scheme (IES) is a hybrid encryption scheme which provides semantic security against an adversary who is allowed to use chosen-plaintext and chosen-ciphertext attacks.

Concrete security

asymptoticasymptotic settingconcrete
In cryptography, concrete security or exact security is a practice-oriented approach that aims to give more precise estimates of the computational complexities of adversarial tasks than polynomial equivalence would allow.

Digital signature

digital signaturesdigitally signeddigitally sign
A digital signature scheme is secure if for every non-uniform probabilistic polynomial time adversary, A

Distributed key generation

The involvement of many parties requires Distributed key generation to ensure secrecy in the presence of malicious contributions to the key calculation.


It may therefore perform several actions of an attacker's choice on an compromised computer, such as changing the Domain Name Server (DNS) settings in order to divert traffic to unsolicited, and potentially illegal and/or malicious domains.

Attacker (disambiguation)

For the term attacker in computer security, see Hacker (computer security), Adversary (cryptography), and Adversary model.''