Can the ransomware encryption key be derived from comparing encrypted and unencrypted files?


– The ransomware encryption key can potentially be derived from comparing encrypted and unencrypted files.


Ransomware is a type of malicious software that infects a computer system, encrypts the files on it, and demands payment in exchange for the decryption key. It has become one of the most significant threats to cybersecurity in recent years, with new strains of ransomware emerging almost every day. One of the challenges faced by cybersecurity experts is finding ways to recover data without paying the ransom demand. This article will explore whether the encryption key can be derived from comparing encrypted and unencrypted files.

The Ransomware Encryption Process

Ransomware typically uses a symmetric encryption algorithm, such as Advanced Encryption Standard (AES), to encrypt data on the infected computer. Symmetric encryption algorithms use the same key for both encryption and decryption. The attacker generates the encryption key when the malware is executed and uses it to encrypt all the files on the system.

Comparing Encrypted and Unencrypted Files

The idea of using comparisons between encrypted and unencrypted files as a means of deriving the ransomware encryption key has been proposed in some research papers. The method involves creating a file containing all possible encryption keys, then comparing each key with the encrypted version of a known unencrypted file. If a match is found, it means that the corresponding key was used to encrypt the file on the infected computer.

Challenges in Deriving the Encryption Key

While the idea of deriving the encryption key from comparing encrypted and unencrypted files may seem straightforward, it presents several challenges. The first challenge is finding a suitable unencrypted file to compare with the encrypted version. If all the files on the infected computer have been encrypted, there will be no unencrypted files available for comparison.

The second challenge is that ransomware often deletes or encrypts shadow copies of files, making it impossible to obtain an original version of the file. Additionally, some strains of ransomware may modify the file structure before encrypting the data, which could make it difficult to recognize the unencrypted version even if it is available.

Alternative Methods for Recovering Encrypted Data

While deriving the encryption key from comparing encrypted and unencrypted files may be challenging, there are other methods that can be used to recover encrypted data. One of the most effective methods is to use a backup of the affected files or system. If a recent backup exists, the encrypted data can be restored without needing to decrypt it.

Another method is to use a decryption tool that has been developed for a particular strain of ransomware. The No More Ransom project is an initiative by law enforcement agencies and cybersecurity companies that provides free decryption tools for various strains of ransomware. However, not all strains are covered, and new strains emerge regularly, making it difficult to keep up with the ever-changing threat landscape.


Deriving the encryption key from comparing encrypted and unencrypted files is a challenging task that requires access to an original version of the file, which may not always be possible. Alternative methods such as using backups or decryption tools are more effective in recovering encrypted data. However, it is essential to have a robust cybersecurity strategy in place, including regular backups and up-to-date antivirus software, to prevent ransomware attacks from occurring in the first place.

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