Known-plaintext attacks, explained

Understanding a known-plaintext attack

As a seasoned cybersecurity analyst with over two decades of experience under my belt, I have seen firsthand the evolving tactics used by malicious actors to breach systems and compromise sensitive data. One such tactic is the known-plaintext attack, which has been around for ages but remains a significant threat in today’s digital landscape.

In a known-plaintext attack (KPA), an attacker utilizes matched sets of both encrypted and original data to decipher the underlying encryption method or secret key.

In this cyber-attack scenario, the hacker possesses not only the encoded information (the ciphertext), but also its original, unaltered form (the plaintext). The attacker then attempts to deduce the specific encryption technique or key by examining the similarities and differences between the two.

For instance, if “blockchain” is substituted as “eorfnfkdlq,” this knowledge might aid an attacker in deciphering other sections of the message that employ the same code. This demonstrates how certain encryption techniques can be compromised when even a minimal amount of information is known, potentially leading to the unraveling of the encoded message.

In simpler terms, this kind of assault exploits flaws in encryption methods, enabling intruders to spot correlations or links between the original message (plaintext) and its encrypted version (ciphertext). If not adequately protected, such attacks using known plaintext can compromise the security of an encryption system.

As a researcher, I frequently employ two prevalent methods in my work: frequency analysis and pattern matching. These strategies aid me significantly in deciphering both plaintext and encrypted messages. Frequency analysis helps me identify the most commonly occurring characters or words, while pattern matching allows me to spot recurring patterns that might reveal hidden information.

• Frequency analysis: Attackers use simple encryption methods where each letter or symbol is replaced with a specific one. By comparing the frequency of letters or patterns in the plaintext and ciphertext, attackers can uncover the key or decode the rest of the message.
• Pattern matching: Bad actors look for repeating patterns. If the same plaintext results in the same ciphertext, they can identify trends in the encrypted text and use them to figure out the encryption algorithm, ultimately decrypting the entire message.

How does a known-plaintext attack work?

An intruder might exploit this known pair by attempting to decipher the underlying encryption technique – a process called “reverse engineering”. Initially, they may not possess the precise key or methodology, but merely having access to a single pair of plain text and encrypted text provides them with an entry point to begin breaking the encryption code.

In essence, possessing a greater number of encrypted message pairs allows an attacker to more quickly deduce the encryption technique and key. Consequently, this simplifies the process of deciphering additional messages that have been encoded in the same manner.

Let’s break down the potential method behind this scenario, building on the earlier “blockchain” and “eorfnfkdlq” analogy:

Steps in a known-plaintext attack

• Collecting known pairs: Attackers gather pairs of plaintext and their corresponding ciphertext. These can be obtained through intercepted communications, data leaks or other means.
• Analyzing the pattern: The attacker compares the letters in the plaintext (“blockchain”) to the corresponding letters in the ciphertext (“eorfnfkdlq”). By studying how each letter in the plaintext transforms into a different letter in the ciphertext, the attacker might notice a pattern. For example, the letter “b” turns into “e,” “l” turns into “o” and so on.
• Guessing the cipher: Based on the changes between the plaintext and ciphertext, the attacker can make educated guesses about the encryption algorithm. For example, if the letters are shifted by a fixed number of positions, the attacker might notice that each letter in “blockchain” has been shifted by a certain number of places in the alphabet. For example, in a Caesar cipher, you might shift each letter by three positions, as seen in the image above.
• Breaking the encryption: Once the attacker figures out the pattern or encryption rule, they can apply that knowledge to decrypt other parts of the message or even future messages that use the same key or algorithm.

Have you heard that the Caesar cipher gets its name from Julius Caesar, as he employed it to secure his confidential communications?

Chosen-plaintext attacks (CPA) vs. known-plaintext attacks (KPA)

In chosen-plaintext attacks, attackers pick their own message (plaintext) and examine the resulting encoded version (ciphertext), while in known-plaintext attacks, the adversaries have some prior understanding or knowledge of the original message.

In simple terms, the key difference between CPA and KPA is:

• Chosen-plaintext attacks: Attackers can select or choose the plaintext they want and study how it is encrypted into ciphertext.
• Known-plaintext attacks: Attackers already have access to some plaintext-ciphertext pairs and use this information to analyze the encryption, without having selected the plaintext themselves.

Understanding these distinctions is essential for developing strong cryptographic defenses.

Have you heard this before? Phishing is a sneaky method used by hackers where they mislead people into disclosing private details like passwords, pretending to be reliable entities. On the other hand, plaintext refers to data or messages that are not encrypted and can be easily read by anyone.

How to protect against a known-plaintext attack?

To ensure security against attacks using predictable data (known-plaintext attacks), it is advisable to implement robust encryption methods, handle encryption keys confidentially, assign distinct keys for each session, and incorporate random elements in the encryption procedures to boost protection.

Opt for encryption algorithms that can resist known-plaintext attacks by employing robust encryption methods. By ensuring that discernible patterns in the original data (plaintext) don’t align with patterns in the encrypted data (ciphertext), contemporary cryptographic algorithms such as the Advanced Encryption Standard (AES) are designed to withstand these types of attacks. AES is a commonly used symmetric encryption algorithm, recognized for its security and efficiency.

Ensure safe control over encryption keys to prevent unauthorized use. Store your keys in secure vaults, regularly update them, and employ robust key creation methods. Furthermore, refrain from encrypting distinct, easily guessable segments of data. Instead, protect against known pairs being exploited by encoding the entire message or file.

Additionally, employ distinct keys for separate sessions and tasks to minimize the effect of known-plaintext attacks as each session utilizes a unique encryption key. Furthermore, keep your systems, libraries, and encryption tools up-to-date. Regular updates often incorporate security patches that address vulnerabilities.

Before encoding your data’s original text (plaintext), it’s wise to append a cryptographic seasoning – a random value – to it. This unique seasoning ensures that each encryption is distinct, even if the same plaintext is encrypted multiple times. Furthermore, opt for encryption techniques that are not susceptible to known-plaintext attacks. Lastly, always conduct thorough research when choosing encryption algorithms.