What is Cryptanalysis? Read a Complete Overview


The study and practice of decrypting and analyzing codes, ciphers, and encrypted text without using the actual key is known as cryptanalysis. It is a way of gaining access to the plain text content of a communication when the decryption key is unavailable.

Define the relevant terms

Cryptology is divided into cryptography (the creation of secret codes) and cryptanalysis (the study of cryptographic algorithms and the splitting of such codewords). A Cryptanalyst is someone who practices Cryptanalysis.

Role of Cryptanalysis

Cryptanalysis plays a significant role in the process of developing robust cryptosystems. If the designers of the cryptosystems did not consider all potential attack vectors, then "security via obscurity" can lead to the implementation of weak cryptosystems.

What does a Cryptanalyst do?

Their work includes identifying any weak points in the cryptosystem. It aids in our understanding of them and our ability to strengthen them and work on the algorithm to produce more secure secret codes. A Cryptanalyst, for example, might attempt to decipher ciphertext to obtain plaintext. It can assist us in determining the plaintext or the encryption key.

What cryptanalytic assaults define

It is essential to attack a cryptographic system to identify its flaws. They are known as cryptanalytic assaults. The attacks depend on the algorithm's nature and knowledge of the essential elements of the plaintext, which can be a standard English document or Java code. So, it is critical to understand the nature of the plaintext before attacking.

Types of Cryptanalytic Attacks

  • Known-Plaintext Analysis (KPA) − Some plaintext-ciphertext combinations are already known in this type of action. To obtain the encryption key, the attacker maps them. This attack is simpler to execute because a large volume of data is already accessible.

  • Chosen-Plaintext Analysis (CPA) − In this attack method, the attacker selects irregular plaintexts, obtains the corresponding ciphertexts, and attempts to decrypt the message. It is as easy to implement as KPA, but the success rate seems minimal.

  • Ciphertext-Only Analysis (COA) − In this attack, the attacker only has a portion of the ciphertext and attempts to deduce the corresponding encryption key and plaintext. It's the most complex to build, but it's also the most likely to be attacked because just ciphertext is required.

Man-in-the-Middle (MITM) Attack

The attacker can intercept the message/key transferred between bidirectional communication partners over a secure communication channel.

Simple Cryptanalytic Techniques

Newer cryptographic algorithms are built to withstand all known cryptanalytic methods. However, a few simple strategies can help assess (and potentially break) the security of older or novice cryptosystems.

Entropy Calculations

Entropy is an indicator of the amount of unpredictability present in a system. A robust cryptographic algorithm should generate ciphertext with large randomness, indicating that the ciphertext contains little or no helpful information that links with the original plaintext or secret key.

As a result, entropy testing is a beneficial tool for identifying encrypted data. While entropy can be calculated by hand, tools such as Binwalk and radare2 include entropy reviewers that can be utilized to distinguish encrypted data within a file.

After identifying encrypted data, one can use other features to help identify the encryption algorithms used. Ciphertext & block length and Function names are examples of helpful information. 

It is possible to determine whether an encryption algorithm is flawed if one can identify the algorithm. The algorithm can also find an encryption key within a file, which can be helpful knowledge.

Analysis of Character Frequency

Modern languages, apart from a good ciphertext, are not random. With enough expertise in a language, it can be possible to assume which letter follows a given series. What letter, for instance, almost always follows the letter Q in English?

The lack of randomness in the language is beneficial for cryptanalysis because it makes weak ciphers easy to break. Substitution and rotational ciphers can be easily broken using character frequency analysis.

Encryption vs. Encoding

Both encoding and encryption are methods of concealing data. Their implementation and effects, however, are vastly different.

For encryption and decryption, encryption requires using a secret key. With knowing this secret key, extracting the plaintext from the ciphertext is possible.

Without a secret key, encoding algorithms perform a reversible operation on data. This means that anyone familiar with the encoding algorithm can overturn it.

Encoding algorithms are frequently used in ransomware as a simple substitute for encryption. They can, however, be easily changed if the encoding algorithm is known.

Encoding in Base64

Base64 encoding is an encoding technique that allows any type of data to be sent over protocols restricted to alphanumeric characters and symbols. This is achieved by mapping three-byte sequences to four-character sets.

This mapping allows you to assign a six-bit sequence (four sets of six characters equals twenty-four bits or three bytes) to one of sixty-four printable symbols, as shown in the table above. The base64 system uses padding to ensure that an input not exactly a multiple of three bytes longer results in an encoded version with one or two equal signs (like =/==) at the end.

This encoding method can be easily recognized thanks to the base64 character set and these equal option signs.

Because Base 64 encoding is used to make otherwise unprintable data printable, it is frequently used to encode encrypted data. Encoding, which can be easily reversed, is occasionally used in place of encryption.

Encoding URLs

Another encoding method used to enable data transmission in a protocol with a limited character set is URL encoding. In this situation, URL encoding aims to make it possible for characters like "?" and. "" reserved in URLs to be used in a domain name or other parts of the URL.

Conclusion

Most contemporary encryption algorithms are resistant to known attacks, and many of those that are "broken" require knowledge of complex mathematics to comprehend the attacks. However, straightforward methods make much older encoding and encryption algorithms easily breakable.

This is advantageous because numerous malware variants rely on these less secure encryption techniques. Understanding fundamental cryptanalytic concepts and methods can be highly beneficial in cybersecurity.

Updated on: 09-Dec-2022

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