LianGuai Encyclopedia | What is a known plaintext attack

LianGuai Encyclopedia | Known plaintext attack

Author: Jagjit Singh, Cointelegraph; Translation: Matsumi, LianGuai

1. Understanding Known Plaintext Attacks

A known plaintext attack (KLianGuai) refers to hackers using known unencrypted and encrypted materials to determine algorithms or encryption keys.

In a known plaintext attack, the attacker can access the encrypted form (ciphertext) of the data and its corresponding plaintext copy (unencrypted form). The attacker attempts to determine the encryption key or algorithm by examining the relationship between the plaintext and ciphertext.

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For example, if “CRYPTO” is encoded as “XUZZA”, knowing this pair would allow the attacker to decode other parts of the message that were also encrypted using the same substitution key. This indicates that even a small amount of knowledge can achieve broader decryption using certain encryption algorithms.

This attack exploits flaws in encryption technology that can identify patterns or connections between plaintext and ciphertext. If not properly prevented, known plaintext attacks can compromise the security of encryption systems.

Two common methods of revealing encryption keys using plaintext and its corresponding encrypted form include frequency analysis and pattern matching. The frequency analysis method uses simple encryption methods and one-to-one letter or symbol substitution. Attackers can discover the key or unlock the rest of the communication by comparing the frequency of specific letters or patterns between known plaintext and related ciphertext.

In the pattern matching method, when the same plaintext produces the same ciphertext, attackers can detect trends. They can identify the encryption algorithm and decrypt the entire message by recognizing patterns in the encrypted text and comparing them with known patterns in the plaintext.

2. How does a known plaintext attack work?

In KLianGuai, attackers can understand important details about encryption methods by analyzing how specific blocks of plaintext are transformed into ciphertext using the same encryption key or algorithm.

The attack involves the following steps:

Collect known pairs

The attacker accumulates original plaintext and relevant encrypted ciphertext obtained through various techniques, such as intercepting communications or data leaks.

Analyze patterns

When plaintext is encrypted to create ciphertext, the attacker compares the patterns, modifications, and transformations that occur. To understand the operations of the encryption process, they search for rule relationships between known plaintext and ciphertext.

Derive the key or algorithm

The attacker attempts to determine critical encryption elements, such as encryption keys, algorithms, or other process parameters, based on the patterns they have noticed. Through this derivation, they can independently replicate the encryption process.

Decrypt other data

The attacker can use the derived key or algorithm to decrypt other encrypted materials that use the same encryption algorithm. This process may reveal confidential information or compromise the security of the encryption system.

3. Choosing Plaintext Attack vs Known Plaintext Attack

The chosen plaintext attack involves the adversary selecting plaintext and analyzing the corresponding ciphertext, while the known plaintext attack occurs when the attacker has partial knowledge of the plaintext.

Understanding the differences between these two types of encryption attacks is crucial for effective encryption defense strategies.

Frequency analysis focuses on examining the occurrence of letters or symbols to determine the encryption algorithm, which is different from classical cryptanalysis that examines patterns and flaws in the ciphertext.

IV. How to defend against known plaintext attacks?

To defend against known plaintext attacks, use strong encryption algorithms, securely manage encryption keys, use unique keys for each session, and add randomness during the encryption process to enhance protection against attacks.

By using robust encryption techniques, choose encryption algorithms that can resist known plaintext attacks. Advanced Encryption Standard (AES) and other modern encryption algorithms can withstand such attacks by preventing patterns in the plaintext from being associated with patterns in the ciphertext. AES is a widely used symmetric encryption algorithm known for its security and efficiency.

Safely manage encryption keys to avoid unauthorized access. Use secure key storage repositories, regularly rotate keys, and utilize strong key generation techniques. Additionally, avoid encrypting discrete, predictable data blocks. To prevent attackers from using known pairs, encrypt the entire message or file.

In addition, use different keys for different sessions and tasks. Since each session will use a different encryption key, the impact of known plaintext attacks will be reduced. Furthermore, keep the system, libraries, and encryption software up to date. Security patches that fix vulnerabilities are often included in updates.

Before encrypting plaintext data, add encryption salts (random values) to make each encryption unique, even if encrypting the same plaintext multiple times. Also, avoid using encryption methods that are susceptible to known plaintext attacks. In other words, conduct proper due diligence when selecting encryption algorithms.

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