Chosen-Ciphertext Attack (CCA)

A chosen-ciphertext attack is one in which cryptanalyst may choose a part of ciphertext and try to obtain the represent decrypted plaintext. This type of attack is generally most applicable to public-key cryptosystems.
A chosen-ciphertext attack ( CCA ) is an assail exemplar for cryptanalysis in which the cryptanalyst gathers information, at least in part, by choosing a ciphertext and obtaining its decoding under an nameless samara. In the attack, an adversary has a chance to enter one or more know ciphertexts into the arrangement and obtain the resulting plaintexts. From these pieces of information the adversary can attempt to recover the shroud secret key used for decoding.

A number of otherwise plug schemes can be defeated under chosen-ciphertext attack. For exemplar, the El Gamal cryptosystem is semantically batten under chosen-plaintext attack, but this semantic security system can be trivially defeated under a chosen-ciphertext fire. early versions of RSA padding used in the SSL protocol were vulnerable to a twist adaptive chosen-ciphertext attack which revealed SSL school term keys. Chosen-ciphertext attacks have implications for some self-synchronizing stream ciphers a well. Designers of tamper-resistant cryptanalytic fresh cards must be particularly aware of these attacks, as these devices may be wholly under the control of an adversary, who can issue a large number of chosen-ciphertexts in an try to recover the hide privy key.

According to RSA :

Cryptanalytic attacks are by and large classified into six categories that distinguish the kind of information the cryptanalyst has available to mount an approach. The categories of attack are listed here roughly in increasing order of the timbre of information available to the cryptanalyst, or, equivalently, in decreasing club of the level of difficulty to the cryptanalyst. The objective of the cryptanalyst in all cases is to be able to decrypt raw pieces of ciphertext without extra information. The ideal for a cryptanalyst is to extract the secret key.

A ciphertext-only attack is one in which the cryptanalyst obtains a sample of ciphertext, without the plaintext associated with it. This data is relatively easy to obtain in many scenarios, but a successful ciphertext-only attack is by and large unmanageable, and requires a very large ciphertext sample. such attack was possible on zero using Code Book Mode where frequency analysis was being used and even thou only the ciphertext was available, it was still potential to finally collect enough data and decipher it without having the winder.

A known-plaintext attack is one in which the cryptanalyst obtains a sample distribution of ciphertext and the corresponding plaintext arsenic well. The known-plaintext attack ( KPA ) or crib is an attack model for cryptanalysis where the attacker has samples of both the plaintext and its code adaptation ( ciphertext ), and is at familiarity to make use of them to reveal further secret information such as secret keys and code books.

A chosen-plaintext attack is one in which the cryptanalyst is able to choose a quantity of plaintext and then obtain the correspond encrypted ciphertext. A chosen-plaintext attack ( CPA ) is an attack model for cryptanalysis which presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the represent ciphertexts. The goal of the attack is to gain some far information which reduces the security system of the encoding system. In the worst case, a chosen-plaintext attack could reveal the schema ‘s secret cardinal.

This appears, at first glance, to be an unrealistic model ; it would surely be improbable that an attacker could persuade a human cryptanalyst to encrypt boastfully amounts of plaintexts of the attacker ‘s choose. Modern cryptanalysis, on the other hand, is implemented in software or hardware and is used for a divers roll of applications ; for many cases, a chosen-plaintext fire is much very feasible. Chosen-plaintext attacks become extremely important in the context of public samara cryptography, where the encoding key is public and attackers can encrypt any plaintext they choose.

Any cipher that can prevent chosen-plaintext attacks is then besides guaranteed to be impregnable against known-plaintext and ciphertext-only attacks ; this is a conservative approach to security.

Two forms of chosen-plaintext attack can be distinguished :

Batch chosen-plaintext attack, where the cryptanalyst chooses all plaintexts before any of them are encrypted. This is frequently the mean of an unqualified practice of “ chosen-plaintext attack ”.

Adaptive chosen-plaintext fire, is a extra case of chosen-plaintext attack in which the cryptanalyst is able to choose plaintext samples dynamically, and alter his or her choices based on the results of previous encryptions. The cryptanalyst makes a series of synergistic queries, choosing subsequent plaintexts based on the information from the previous encryptions.

Non-randomized ( deterministic ) public identify encoding algorithms are vulnerable to simple “ dictionary ” -type attacks, where the attacker builds a board of probably messages and their equate ciphertexts. To find the decoding of some ascertained ciphertext, the attacker merely looks the ciphertext up in the table. As a resultant role, public-key definitions of security under chosen-plaintext attack necessitate probabilistic encoding ( i.e., randomized encoding ). conventional symmetrical ciphers, in which the same identify is used to encrypt and decrypt a text, may besides be vulnerable to early forms of chosen-plaintext attack, for exemplar, differential cryptanalysis of block ciphers.

An adaptive-chosen-ciphertext is the adaptive version of the above attack. A cryptanalyst can mount an attack of this character in a scenario in which he has free use of a musical composition of decoding hardware, but is unable to extract the decoding key from it.

An adaptive chosen-ciphertext attack ( abbreviated as CCA2 ) is an interactional form of chosen-ciphertext attack in which an attacker sends a phone number of ciphertexts to be decrypted, then uses the results of these decryptions to select subsequent ciphertexts. It is to be distinguished from an immaterial chosen-ciphertext attack ( CCA1 ).

The goal of this attack is to gradually reveal information about an code message, or about the decoding key itself. For public-key systems, adaptive-chosen-ciphertexts are generally applicable merely when they have the place of ciphertext malleability — that is, a ciphertext can be modified in specific ways that will have a predictable effect on the decoding of that message.

A Plaintext Only Attack is just a bogus detractor. If you have the plaintext only then there is no need to perform any attack

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