What Is Cryptanalysis?

Cryptanalysis is the study and discovery of vulnerabilities within cryptographic algorithms that can be used to decrypt ciphertext without the secret key.

Written by Anthony Corbo
Published on Jan. 03, 2023
What Is Cryptanalysis?
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Katlyn Gallo | Jan 09, 2023

Cryptanalysis is the study and discovery of vulnerabilities within cryptographic algorithms that can be used to decrypt ciphertext without knowledge of the secret key. Several forms of cryptanalysis can be used to attack cryptographic messages, ranging from the interception of messages within unsecured communication channels to the matching of plaintext based on the same algorithm techniques. Cryptanalysis also includes measures taken to stop attackers from decoding cryptographic algorithms.

Is Cryptanalysis Still Used?

Yes, cryptanalysis is used to discern the plaintext encoded within a cryptographic message. This is done through the use of various methods that provide an attacker with information that can be used to decode the encoded ciphertext. The different forms of cryptanalysis are based upon the information the attacker has in their possession and the means of decryption used. 

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Types of Cryptanalysis

There are three generic forms of cryptanalysis: ciphertext-only, known ciphertext/plaintext pairs and chosen plaintext or chosen ciphertext.

In ciphertext-only cryptanalysis, the attacker has the ciphertext available to them for decoding. In known ciphertext/plaintext pair cryptanalysis, attackers will know some element of the plaintext and will be able to match likely elements of the ciphertext to the known plaintext. For example, a computer session may begin with “LOG IN.”

Deciphering this string of text will also allow the attacker to decrypt plaintext that matches the deciphered ciphertext throughout the message. Chosen plaintext or chosen ciphertext cryptanalysis occurs when the attacker unwittingly causes either the transmitter to encrypt plaintext or the receiver to decrypt ciphertext. This provides the attacker with an abundance of knowledge, possibly even knowledge of the entire message’s contents.

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What Is the Primary Goal of Cryptanalysis?

Cryptanalysis is used to understand the contents of protected or encrypted messages and data in order to gain access to either in-transit or at-rest data. Attackers using cryptanalysis may have several goals for doing so, but the ultimate goal is always some degree of cryptographic decryption through either the ciphertext or plain text. 

Some specific goals associated with cryptanalysis include a total break (the locating of the secret key), global deduction (the locating of a functionally equivalent algorithm for encryption and decryption without knowledge of the secret key), information deduction (the acquiring of a portion of information about the plaintext or ciphertext that was not previously known), and the distinguishing of the algorithm (giving the attacker the ability to determine the encryption’s output from a random selection of plaintext).

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What Does a Cryptanalyst Do?

Cryptanalysts can be hired to find security weaknesses, potential data leak causes, discover evidence from encrypted messages and more.

Cryptanalysts are often associated with government agencies or law enforcement, hired to ensure agency encryption methods are up to par with the current standards in cybersecurity and engage in the deciphering of encrypted messages. Cryptanalysts do this by purposefully exploiting weaknesses so fixes can be applied. As mentioned, government organizations often employ cryptanalysts to decipher encrypted communications and law enforcement agencies will hire cryptanalysts to decode encrypted messages within evidence or testify as experts on a case.

Regardless of their industry or ethics, cryptanalysts must have a strong understanding of mathematics, ciphers, codes, and encryption systems, with daily responsibilities including analyzing intelligence information, diagnosing weaknesses within cryptographic algorithms, developing new cryptanalysis tools and more.

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