HOW RANSOMWARE ENCRYPTION WORKS
Ransomware is a type of malware that encrypts files on a victim’s computer or network, rendering them inaccessible, and then demands a ransom (usually in cryptocurrency) for the decryption key that will allow the victim to regain access to their data. The encryption is a key part of the attack because it locks the victim’s files in a way that makes them unreadable without the decryption key, which the attacker holds.
Here’s a step-by-step breakdown of how ransomware encryption works:
The first step in a ransomware attack is infecting the victim’s system. This can occur through various methods:
- Phishing Emails: Malicious attachments or links in emails trick users into downloading the ransomware.
- Malicious Ads (Malvertising): Ransomware can be delivered through ads on compromised websites.
- Exploiting Vulnerabilities: The attacker may exploit vulnerabilities in unpatched software or operating systems to gain access.
- Drive-by Downloads: Downloading infected files from untrusted sources can also introduce ransomware.
- Remote Desktop Protocol (RDP) Exploits: Ransomware can be delivered by exploiting weak or stolen credentials on exposed RDP servers.
Once the malware is executed, it typically runs silently in the background, preparing for the encryption process.
Once the ransomware is running, it starts the encryption process. Here’s how it typically works:
a. Key Generation and Encryption Algorithms
Most modern ransomware uses strong encryption algorithms to lock the files, typically AES (Advanced Encryption Standard) or RSA. These are two commonly used encryption standards:
- AES Encryption (Symmetric): AES is a symmetric encryption algorithm, meaning the same key is used for both encryption and decryption. Ransomware will generate a random AES key for each victim and encrypt files with it.
- RSA Encryption (Asymmetric): RSA is an asymmetric encryption algorithm that uses two keys: a public key (which is available to anyone) and a private key (which is kept secret by the attacker). The attacker encrypts the AES key (used to encrypt files) with their private RSA key, and this encrypted AES key is what the victim needs in order to decrypt their files.
b. File Targeting and Encryption
The ransomware will scan the victim’s computer or network for specific types of files (e.g., documents, spreadsheets, databases, images, etc.). It will usually avoid system files or files that are critical for the operating system to prevent the victim from realizing the attack too quickly.
- The ransomware encrypts these files using the generated AES key. Each file is scrambled using the AES encryption algorithm, and the result is unreadable without the correct decryption key.
- During encryption, the ransomware may also change the file extensions (e.g.,
.docxto.lockedor.crypt) to indicate that the files have been encrypted.
c. Key Storage and Communication
After the encryption process, the ransomware typically uploads the AES encryption key to a remote server controlled by the attacker. It then encrypts the key with an RSA public key. Only the attacker has the corresponding RSA private key needed to decrypt the AES key.
- Public/Private Key Pair: The public key is typically hard-coded into the ransomware, while the private key is kept secret and used by the attacker to decrypt the AES key.
- The private RSA key is kept securely by the attacker and stored on their server.
After encryption, the victim is notified that their files have been locked. The attacker usually leaves a ransom note (a text file, HTML page, or a pop-up message) on the victim’s system. The note will typically contain the following details:
- Ransom Amount: The attacker demands payment, often in cryptocurrency like Bitcoin or Monero due to its relative anonymity.
- Payment Instructions: Details on how to send the ransom and a deadline for payment. Often, the attacker will threaten to destroy the decryption key or increase the ransom if the victim doesn’t pay within the specified time.
- Contact Information: Some ransomware variants provide a way for the victim to communicate with the attacker, usually via a Tor-based site, email address, or messaging system.
If the victim decides to pay the ransom (which is not recommended), the attacker will (theoretically) send the decryption key. The decryption process generally works as follows:
a. AES Decryption with RSA Private Key
- After receiving the ransom, the attacker provides the victim with the RSA-encrypted AES key. The victim cannot decrypt their files without the correct AES key.
- The victim must then use the RSA private key (which only the attacker possesses) to decrypt the AES key.
b. Decrypting Files
- Once the victim has the correct AES key, they can use it to decrypt their files and regain access to them. At this point, the files are restored to their original, readable format.
c. No Guarantee of Decryption
It’s important to note that even if the victim pays the ransom, there’s no guarantee the attacker will provide the decryption key. Many victims have paid the ransom but received no decryption key or only partial recovery of their data.
Ransomware attacks have evolved over time, and some newer variants have added complexity to the encryption process:
- Double Encryption: Some ransomware strains use dual encryption techniques, first encrypting files with one algorithm (e.g., AES) and then encrypting the AES key itself using another algorithm (e.g., RSA).
- Exfiltration and Threats: In addition to encrypting files, some ransomware variants now also exfiltrate sensitive data (e.g., documents, emails, financial records) before encryption. They threaten to release or sell this data unless the ransom is paid.
- Fileless Ransomware: Newer variants sometimes operate in a fileless manner, meaning they don’t store their payload on the disk. Instead, they use legitimate system tools (like PowerShell) to execute malicious scripts, making detection harder.
- Ransomware-as-a-Service (RaaS): Some cybercriminals now offer ransomware kits for other attackers to use, increasing the reach and scale of ransomware campaigns.
While ransomware encryption is powerful, there are several measures that can reduce the likelihood of infection and mitigate the impact:
a. Regular Backups
- Regularly back up your files to offline or cloud-based storage. If you’re infected, you can restore your files without paying the ransom.
b. Software and System Updates
- Keep your operating system, software, and applications up-to-date to patch vulnerabilities that ransomware might exploit.
c. Antivirus Software
- Use reputable antivirus software to detect and block ransomware before it can start encrypting your files.
d. Network Segmentation
- Segregate sensitive data and critical systems within your network. This helps prevent the spread of ransomware across the entire network.
e. User Education
- Train users to avoid clicking on suspicious links, opening unverified email attachments, or visiting untrusted websites.
f. Multi-Factor Authentication (MFA)
- Use multi-factor authentication (MFA) to make it harder for attackers to gain unauthorized access to systems.
g. Ransomware Detection Tools
- Employ ransomware-specific detection tools that can identify unusual behavior associated with ransomware (e.g., rapid file encryption).
Ransomware encryption is a powerful and dangerous attack method used by cybercriminals to lock victims out of their files and demand a ransom for the decryption key. The encryption typically involves strong algorithms like AES and RSA, and while paying the ransom may restore access to the data, it does not guarantee that the attacker will actually release the decryption key. The best defense against ransomware is prevention through regular backups, security patches, and user awareness, combined with good cybersecurity hygiene to minimize the risk of infection.
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