Chosen-plaintext attack

Chosen-plaintext attack

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 corresponding ciphertexts. The goal of the attack is to gain some further information which reduces the security of the encryption scheme. In the worst case, a chosen-plaintext attack could reveal the scheme's secret key.

This appears, at first glance, to be an unrealistic model; it would certainly be unlikely that an attacker could persuade a human cryptographer to encrypt large amounts of plaintexts of the attacker's choosing. Modern cryptography, on the other hand, is implemented in software or hardware and is used for a diverse range of applications; for many cases, a chosen-plaintext attack is often very feasible. Chosen-plaintext attacks become extremely important in the context of public key cryptography, where the encryption key is public and attackers can encrypt any plaintext they choose.

Any cipher that can prevent chosen-plaintext attacks is then also guaranteed to be secure 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 often the meaning of an unqualified use of "chosen-plaintext attack".
  • Adaptive chosen-plaintext attack, where the cryptanalyst makes a series of interactive queries, choosing subsequent plaintexts based on the information from the previous encryptions.

Non-randomized (deterministic) public key encryption algorithms are vulnerable to simple "dictionary"-type attacks, where the attacker builds a table of likely messages and their corresponding ciphertexts. To find the decryption of some observed ciphertext, the attacker simply looks the ciphertext up in the table. As a result, public-key definitions of security under chosen-plaintext attack require probabilistic encryption (i.e., randomized encryption). Conventional symmetric ciphers, in which the same key is used to encrypt and decrypt a text, may also be vulnerable to other forms of chosen-plaintext attack, for example, differential cryptanalysis of block ciphers.

A technique termed Gardening was used by Allied codebreakers in World War II who were solving messages encrypted on the Enigma machine. Gardening can be viewed as a chosen-plaintext attack.

See also


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Chosen-plaintext attack — Die Kryptoanalyse (in neueren Publikationen auch: Kryptanalyse) bezeichnet im ursprünglichen Sinne das Studium von Methoden und Techniken, um Informationen aus verschlüsselten Texten zu gewinnen. Diese Informationen können sowohl der verwendete… …   Deutsch Wikipedia

  • Chosen-ciphertext attack — A chosen ciphertext attack (CCA) is an attack model for cryptanalysis in which the cryptanalyst gathers information, at least in part, by choosing a ciphertext and obtaining its decryption under an unknown key. In the attack, an adversary has a… …   Wikipedia

  • Chosen-Plaintext-Attacke — Die Kryptoanalyse (in neueren Publikationen auch: Kryptanalyse) bezeichnet im ursprünglichen Sinne das Studium von Methoden und Techniken, um Informationen aus verschlüsselten Texten zu gewinnen. Diese Informationen können sowohl der verwendete… …   Deutsch Wikipedia

  • Chosen Plaintext — Die Kryptoanalyse (in neueren Publikationen auch: Kryptanalyse) bezeichnet im ursprünglichen Sinne das Studium von Methoden und Techniken, um Informationen aus verschlüsselten Texten zu gewinnen. Diese Informationen können sowohl der verwendete… …   Deutsch Wikipedia

  • Known-plaintext attack — The known plaintext attack (KPA) is an attack model for cryptanalysis where the attacker has samples of both the plaintext (called a crib), and its encrypted version (ciphertext). These can be used to reveal further secret information such as… …   Wikipedia

  • Adaptive Chosen Plaintext — Die Kryptoanalyse (in neueren Publikationen auch: Kryptanalyse) bezeichnet im ursprünglichen Sinne das Studium von Methoden und Techniken, um Informationen aus verschlüsselten Texten zu gewinnen. Diese Informationen können sowohl der verwendete… …   Deutsch Wikipedia

  • Attack model — Attack models or attack typesref|secondname specify how much information a cryptanalyst has access to when cracking an encrypted message. Some common attack models are: *Ciphertext only attack *Known plaintext attack *Chosen plaintext attack… …   Wikipedia

  • Chosen — can mean: Chosen people, people who believe they have been chosen by a higher power to do a certain thing including Jews as a chosen people Contents 1 Korean 2 Cryptanalysis 3 Popular culture …   Wikipedia

  • Chosen Text — Die Kryptoanalyse (in neueren Publikationen auch: Kryptanalyse) bezeichnet im ursprünglichen Sinne das Studium von Methoden und Techniken, um Informationen aus verschlüsselten Texten zu gewinnen. Diese Informationen können sowohl der verwendete… …   Deutsch Wikipedia

  • Plaintext-aware encryption — Plaintext awareness is a notion of security for public key encryption. A cryptosystem is plaintext aware if it is difficult for any efficient algorithm to come up with a valid ciphertext without being aware of the corresponding plaintext.From a… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”