How does ransomware store its decryption keys

Question

Ransomware encrypts files and demands payment for decryption, but how do attackers manage and store decryption keys, and what techniques are used to recover data without paying the ransom?

Answer 1

​Ransomware operates by encrypting a victim's files and demanding payment for their decryption. The management and storage of decryption keys by attackers are central to this process. Understanding these mechanisms is crucial for developing strategies to recover data without succumbing to ransom demands.​

Decryption Key Management in Ransomware

Attackers employ various cryptographic techniques to manage decryption keys securely:​

1. Symmetric Encryption with Embedded Keys: Some ransomware variants use symmetric encryption algorithms (e.g., AES) with a unique key for each victim. This key may be embedded within the ransomware code or stored in a specific location on the infected system.​

2. Asymmetric Encryption (Public/Private Key Pairs): More sophisticated ransomware utilizes asymmetric encryption. For instance, the ransomware generates a unique symmetric key to encrypt the victim's files and then encrypts this key using the attacker's public RSA key. The encrypted symmetric key is often appended to the encrypted files or stored in a separate file on the system. Decryption requires the attacker's private RSA key, which they promise to provide upon payment.​

3. Hybrid Encryption Approaches: Many ransomware strains combine both symmetric and asymmetric encryption methods. They encrypt files with a symmetric key for efficiency and then encrypt this key with an asymmetric public key. The encrypted symmetric key is stored locally, necessitating the attacker's private key for decryption.​

Techniques for Data Recovery Without Paying Ransom

Recovering data without yielding to ransom demands is challenging but possible through several approaches:

1. Utilize Available Decryption Tools: Security researchers and organizations have developed decryption tools for specific ransomware variants. Resources like the No More Ransom Project offer a repository of keys and applications that can decrypt data locked by various types of ransomware. It's advisable to check such platforms to determine if a decryption solution exists for the ransomware in question.

2. Restore from Backups: Maintaining regular, offsite, and immutable backups is one of the most effective defenses against ransomware. If backups are available and unaffected by the ransomware, they can be used to restore encrypted files without paying the ransom.

3. Seek Professional Data Recovery Services: In instances where decryption tools are unavailable and backups are nonexistent or compromised, professional data recovery services may assist. Companies like Ontrack specialize in recovering data from ransomware-encrypted or wiped servers, utilizing proprietary tools and techniques.

4. Leverage Memory Forensics: Some ransomware variants may expose encryption keys in system memory during the encryption process. By capturing and analyzing the system's memory (a process known as memory forensics), it's sometimes possible to extract these keys and decrypt the files. However, this technique requires specialized knowledge and tools, and its success varies depending on the ransomware's design.

Preventative Measures

Preventing ransomware infections is paramount. Implementing robust security practices, such as educating employees about phishing attacks, regularly updating software, enabling multi-factor authentication, and using comprehensive antivirus programs, can significantly reduce the risk of ransomware attacks.