Cryptanalytic Attack

A cryptographic analytic attack or cryptanalytic attack is an algebraic manipulation that attempts to reduce the complexity of a cryptographic algorithm. Analytic attacks focus on the logic of the algorithm itself.

Cryptanalytic Attack Techniques

Cryptanalytic attack techniques featured on this post:

  • Ciphertext-only
  • Known plaintext
  • Chosen plaintext
  • Chosen ciphertext
  • Meet in the middle

Ciphertext-only

Ciphertext-only is a cryptanlytic attack where the attacker has only the ciphertext message.

Known plaintext

Known plaintext is a cryptanalytic attack where the attacker has a copy of the encrypted message along with the plaintext message used to generate the ciphertext.

Chosen plaintext

Chosen plaintext is a cryptanalytic attack where the attacker obtains the ciphertexts correspoindg to a set of plaintexts of their own choosing.

This allows the attacker to attempt to derive the key used and thus decrypt other messages encrypted with that key. This can be difficult, but not impossible.

Differential cryptanalysis is an advanced methods of chosen plaintext attack.

Chosen ciphertext

Chosen ciphertext is an cryptanalytic attack where the attacker has the ability to decrypt chosen portions of the ciphertext message and use the decrypted portion of the message to discover the key.

Meet in the middle

Meet in the middle is a cryptanalytic attack used to defeat algorithms using two rounds of encryption.

The attacker uses a known plaintext message. The plaintext is then encrypted using every possible key (k1), and the equivalent ciphertext is decrypted using all possible keys (k2). When a match is found, the corresponding pair (k1, k2) represents both portions of the double encryption.

This type of attack generally takes only double the time necessary to break a single round of encryption (2ˆn rather that the anticipated 2ˆn * 2ˆn), offering minimal added protection.

Meet in the middle was successful used against deprecated algorithms like Double DES (2DES), that was based on the already vulnerable DES algorithm.

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External references

  • M. Chapman et al; “CISSP Study Guide 9th Edition”, chapter 7 “PKI and Cryptographic Applications”, section “Cryptographic attacks”, pp. 298-301; Wiley, 2021

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