In computer security, a cold boot attack (or to a lesser extent, a platform reset attack) is a type of side channel attack in which an attacker with physical access to a computer performs a memory dump of a computer's random-access memory (RAM) by performing a hard reset of the target machine. Typically, cold boot attacks are used for retrieving encryption keys from a running operating system for malicious or criminal investigative reasons. The attack relies on the data remanence property of DRAM and SRAM to retrieve memory contents that remain readable in the seconds to minutes following a power switch-off.
An attacker with physical access to a running computer typically executes a cold boot attack by cold-booting the machine and booting a lightweight operating system from a removable disk to dump the contents of pre-boot physical memory to a file. An attacker is then free to analyze the data dumped from memory to find sensitive data, such as the keys, using various forms of key finding attacks. Since cold boot attacks target random-access memory, full disk encryption schemes, even with a trusted platform module installed are ineffective against this kind of attack. This is because the problem is fundamentally a hardware (insecure memory) and not a software issue. However, malicious access can be prevented by limiting physical access and using modern techniques to avoid storing sensitive data in random-access memory.
Technical details
DIMM memory modules gradually lose data over time as they lose power, but do not immediately lose all data when power is lost. With certain memory modules, the time window for an attack can be extended to hours or even a week by cooling them with freeze spray and liquid nitrogen. Furthermore, as the bits disappear in memory over time, they can be reconstructed, as they fade away in a predictable manner. Consequently, an attacker can perform a memory dump of its contents by executing a cold boot attack. The ability to execute the cold boot attack successfully varies considerably across different systems, types of memory, memory manufacturers and motherboard properties, and may be more difficult to carry out than software-based methods or a DMA attack. While the focus of current research is on disk encryption, any sensitive data held in memory is vulnerable to the attack.
Attackers execute cold boot attacks by forcefully and abruptly rebooting a target machine and then booting a pre-installed operating system from a USB flash drive, CD-ROM or over the network. In cases where it is not practical to hard reset the target machine, an attacker may alternatively physically remove the memory modules from the original system and quickly place them into a compatible machine under the attacker's control, which is then booted to access the memory. Further analysis can then be performed against the data dumped from RAM.
A similar kind of attack can also be used to extract data from memory, such as a DMA attack that allows the physical memory to be accessed via a high-speed expansion port such as FireWire. A cold boot attack may be preferred in certain cases, such as when there is high risk of hardware damage. Using the high-speed expansion port can short out, or physically damage hardware in certain cases.
Uses
Cold boots attacks are typically used for digital forensic investigations, malicious purposes such as theft, and data recovery.
Digital forensics
In certain cases, a cold boot attack is used in the discipline of digital forensics to forensically preserve data contained within memory as criminal evidence. For example, when it is not practical to preserve data in memory through other means, a cold boot attack may be used to perform a dump of the data contained in random-access memory. For example, a cold boot attack is used in situations where a system is secured and it is not possible to access the computer. A cold boot attack may also be necessary when a hard disk is encrypted with full disk encryption and the disk potentially contains evidence of criminal activity. A cold boot attack provides access to the memory, which can provide information about the state of the system at the time such as what programs are running.
Malicious intent
A cold boot attack may be used by attackers to gain access to encrypted information such as financial information or trade secrets for malicious intent.