Adaptive chosen-ciphertext attack


Adaptive chosen-ciphertext attack

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

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

Practical attacks

Adaptive-chosen-ciphertext attacks were largely considered to be a theoretical concern until 1998, when Daniel Bleichenbacher of Bell Laboratories demonstrated a practical attack against systems using RSA encryption in concert with the PKCS#1 v1 encoding function, including a version of the Secure Socket Layer (SSL) protocol used by thousands of web servers at the time.

The Bleichenbacher attacks took advantage of flaws within the PKCS #1 function to gradually reveal the content of an RSA encrypted message. Doing this requires sending several million test ciphertexts to the decryption device (eg, SSL-equipped web server.) In practical terms, this means that an SSL session key can be exposed in a reasonable amount of time, perhaps a day or less.

Preventing attacks

In order to prevent adaptive-chosen-ciphertext attacks, it is necessary to use an encryption or encoding scheme that limits ciphertext malleability. A number of encoding schemes have been proposed; the most common standard for RSA encryption is Optimal Asymmetric Encryption Padding (OAEP). Unlike ad-hoc schemes such as the padding used in the early versions of PKCS#1, OAEP has been proven secure under the random oracle model. OAEP was incorporated into PKCS#1 as of version 2.0 published in 1998 as the now-recommended encoding scheme, with the older scheme still supported but not recommended for new applications.

References

* Daniel Bleichenbacher, Chosen Ciphertext Attacks Against Protocols Based on the RSA Encryption Standard PKCS #1, CRYPTO 1998, pp1–12.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • 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

  • Adaptive Chosen Ciphertext — 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 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… …   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

  • Adaptive 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

  • 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

  • Ciphertext indistinguishability — is a property of many encryption schemes. Intuitively, if a cryptosystem possesses the property of indistinguishability, then an adversary will be unable to distinguish pairs of ciphertexts based on the message they encrypt. The property of… …   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

  • Ciphertext — The Zimmermann Telegram (as it was sent from Washington to Mexico) encrypted as ciphertext. This article is about encrypted information. For an overview of cryptographic technology in general, see Cryptography. In cryptography, ciphertext (or… …   Wikipedia


Share the article and excerpts

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

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.