2023-6-16 16:0:59 Author: blog.elcomsoft.com(查看原文) 阅读量:16 收藏
In the digital age, where information is a precious commodity and evidence is increasingly stored in virtual realms, the importance of preserving digital evidence has become a must in modern investigative practices. However, the criticality of proper handling is often overlooked, potentially jeopardizing access to crucial data during an investigation. In this article, we will once again highlight the importance of meticulous preservation techniques and live session analysis to prevent the loss of digital evidence.
Why password recovery is not (always) an answer
Password recovery tools such as Elcomsoft Distributed Password Recovery are commonly used to recover access to encrypted evidence by attacking (and recovering) the original plain-text password. It is important to realize that most data formats are designed specifically to withstand brute-force attacks. In real life, the attack will probably take a long time, and a chance to break a password to an encrypted container with brute force is far from a guarantee. We collected and analyzed information published about some 53 cases involving encryption, and found out that encryption was only successfully broken in 10 cases. In other words, we strongly recommend performing other types of analysis (and collecting as much supplementary information as possible) before resorting to password recovery techniques.
For example, this is how fast our tool can try VeraCrypt passwords depending on the key generation function and encryption method used. The speed of around 1,000 passwords per second means that even the simplest password consisting of only 6 English letters and no numbers will take 3.5 days to break. As for a typical 8-character password, which includes an unknown mixture of numbers, lowercase and uppercase English letters, breaking it through brute-force would consume nearly 7,000 years. Even if you were to enhance the attack by employing a distributed network of computers, each equipped with several potent GPU accelerators, we would still be facing years, not days, of persistent attacks. A password more complex than that would leave the brute-force attack no chances.
The challenge of encrypted disks and virtual machines
One of the primary challenges in digital forensics lies in decrypting data stored on encrypted disks or containers. Encrypted disks, such as Windows BitLocker and Apple FileVault2, are designed to be resistant to “cold” attacks. Analyzing a live session before shutting down a computer can aid in extracting encryption keys, rendering lengthy brute-force attacks unnecessary. Extracting BitLocker keys can be accomplished through Windows command-line tools (assuming the account in question has administrative access to the system), while third-party disk encryption tools may be dealt with by capturing a full memory dump to locate on-the-fly encryption keys (OTFE keys) with Elcomsoft Forensic Disk Decryptor or similar tools. Shutting down the computer unmounts encrypted disks and containers and clears OTFE keys from the computer’s memory.
Virtual machines in general offer multiple benefits, and the main one is the complete isolation from the normal working environment. Virtual machines are also a tool commonly used in the criminal world. Many types of virtual machines can be securely encrypted. Using an encrypted VM gives criminals an opportunity to cover their activities under a virtual umbrella, reducing the risks of an accidental leak of incriminating evidence. Shutting down a computer prematurely can deny access to critical information stored within encrypted virtual machines.
Preserving volatile virtual machines and private chats sessions
Volatile virtual machines pose a unique challenge for investigators. Unlike their persistent counterparts, volatile VMs do not commit changes to the container, leaving the VM image file unaltered and potentially void of incriminating evidence. By shutting down a computer hosting a volatile VM, investigators risk losing vital changes and activity history within the VM.
In a fashion similar to encrypted VMs, certain instant messaging applications employ volatile private chat sessions, where all data resides solely in the computer’s RAM instead of being stored in a database on the disk. Powering off the computer erases all traces of these confidential communications.
The issue of plausible deniability in hidden containers
Hidden containers, an integral part of modern disk encryption techniques, are designed to provide users with the shield of plausible deniability. Without knowledge of the correct password and encryption settings, access to hidden containers becomes impossible, making their content and even existence unprovable.
Figure 1: VeraCrypt standard encrypted container. A password unlocks and mounts the encrypted volume. Unless the container is stored on an SSD drive with trim passthrough, distinguishing between encrypted data and random data is impossible.
Figure 2: VeraCrypt hidden container. One password unlocks and mounts the standard encrypted volume, while a different password must be used to unlock and mount the hidden volume.
The essence of hidden crypto containers lies in their ability to camouflage sensitive data within the main encrypted storage container. The main and hidden containers use different passwords, and may even use different encryption settings. The perpetrator may give out a password to the main container, leaving forensic experts in a situation where incriminating evidence becomes not only inaccessible but even its existence transforms into an unprovable uncertainty.
Conclusion
Securing access to crucial digital evidence poses a challenge. In the world of digital forensics, the right handling of digital evidence can make all the difference. By adhering to proper preservation steps, investigators can avoid the loss of vital evidence stored in encrypted disks, virtual machines, private chats, hidden containers, and more.
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