DOCSLIB.ORG

FPGA-Accelerated Key Search for Cold-Boot Attacks Against AES

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
FPGA-Accelerated Key Search for Cold-Boot Attacks Against AES FPGA-accelerated Key Search for Cold-Boot Attacks against AES Heinrich Riebler, Tobias Kenter, Christoph Sorge, and Christian Plessl Department of Computer Science, University of Paderborn 33098 Paderborn, Germany Email: f heinrich.riebler — kenter — christoph.sorge — christian.plessl [email protected] Abstract—Cold-boot attacks exploit the fact that DRAM have changed their value. The second goal of the attacker— contents are not immediately lost when a PC is powered off. which poses the algorithmic and computational challenge—is Instead the contents decay rather slowly, in particular if the to first identify the key in the memory dump, and then to DRAM chips are cooled to low temperatures. This effect opens an correct the errors. If successful, the full disk encryption can attack vector on cryptographic applications that keep decrypted be circumvented using the recovered key. keys in DRAM. An attacker with access to the target computer can reboot it or remove the RAM modules and quickly copy The remainder of this paper is structured as follows. In the RAM contents to non-volatile memory. By exploiting the Section II we discuss related work, in particular the AES key known cryptographic structure of the cipher and layout of the key schedule and the Maxeler data flow system. In Section III we data in memory, in our application an AES key schedule with present the design of the key search procedure for identifying redundancy, the resulting memory image can be searched for key schedules in decayed memory dumps. In Section IV sections that could correspond to decayed cryptographic keys; then, the attacker can attempt to reconstruct the original key. we compare the performance of our accelerator with a CPU However, the runtime of these algorithms grows rapidly with implementation. Finally, we draw conclusions in Section V. increasing memory image size, error rate and complexity of the bit error model, which limits the practicability of the approach. II. BACKGROUND AND RELATED WORK In this work, we study how the algorithm for key search In this section, we describe related work, the foundations can be accelerated with custom computing machines. We present of cold-boot attacks, and our accelerator system. While FPGAs an FPGA-based architecture on a Maxeler dataflow computing have been used for many cryptographic applications and im- system that outperforms a software implementation up to 205x, plementations of the AES algorithm are available (e. g. [4]), which significantly improves the practicability of cold-attacks this is to our knowledge the first work that uses FPGAs for against AES. accelerating cold-boot attacks. I. INTRODUCTION A. Background on Cold-Boot Attacks Protecting the integrity and confidentiality of information The first step of a cold-boot attack is to retrieve the memory is gaining importance in our society. As a reaction individuals content, e.g. by cooling down the memory chips and installing and companies are increasingly using full disk encryption to them on another machine. The resulting memory image has protect access to sensitive data. The most commonly used full to be searched for keys in the next step. Given the possibility disk encryption tools use the symmetric block cipher AES [1]. of bit errors (due to memory decay), cryptographic keys may During runtime, these tools keep the secret key material in not conform exactly to the expected structure. An error model memory, because the key is required for any encryption and is used to decide whether a key candidate is plausible. Once decryption operation. Keeping the key in memory was assumed a plausible candidate has been identified, the original key can to be secure, because the main memory (DRAM) was expected be reconstructed using the same or a different error model. to quickly change into a default state when removing the In recent years, seminal work for efficiently finding [3] and power supply. This assumption has however been invalidated reconstructing [5] AES keys in memory dumps has been by security experts [2]. They have shown that the memory presented. However, these methods either rely on a heuristic contents decay surprisingly slowly over time. The decay can parameter or an idealized, perfect asymmetric decay model, be slowed further by cooling the DRAM chips, which opens which assumes that memory bits can flip only in one direction. the possibility to attack the secret keys and thus full disk For more realistic decay models and higher error rates, the encryption solutions. runtimes of cold-boot attacks strongly increase on general- purpose CPUs [6]. Cold-boot attacks [3] exploit these observations. The attack requires physical access to a machine with a secret key in main B. AES Key Schedule memory, for example, a computer that is running a screen lock while the user is absent. The first goal of the attacker is to AES is a commonly used encryption algorithm. In par- obtain a copy of the complete main memory, for example by ticular, popular tools for the encryption of file systems, like rebooting the machine from a USB thumb drive that quickly TrueCrypt, use AES as their default block cipher. The AES dumps the DRAM contents to non-volatile Flash memory. If key is a 128, 192, or 256 bit (pseudo) random sequence of the reboot process is quick, only a small fraction of the bits will bits without any structure; a naive brute-force attack on AES protected data is thus impractical. However, for performance MPC-C Plattform reasons, not only the AES key itself, but the complete so-called DFE PCIe key schedule is kept in memory. The key schedule is comprised PCIe of the master key and a (key size dependent) number of round keys. Since the actual encryption operation requires the DRAM Memory complete key schedule, the schedule is usually pre-computed Controller and stored as a contiguous array in the main memory. Each DRAM round consists of a certain number of transformations, which are defined by the AES key expansion function [7]. Figures 1 FPGA FPGA FPGA FPGA and 2 show how the 10 round keys in the AES-128 key x86 CPU card card card card schedule are generated from the master key, which is stored as the first row (round 0) in the key schedule. The round keys 1– PCI Express 10, which form the complete key schedule, are derived using Maxeler Design Flow two different functions. The first word in each round key is Original computationally Application Manager computed by applying a complex operation using word 0 and application intensive components Kernel(s) Configuration word 3 of the preceding round key, as illustrated in Fig. 2. (.c, .f) The remaining words 1–3 of each round key are computed by Compiler/ HW HW build a simple XOR operation between the word of the previous MaxCompiler Linker Accelerator or simulation round key and the previous word of the same round key, see Fig. 1. Taking the structure of the whole key schedule into account increases the available information and creates a Fig. 3. Maxeler MPC-C platform architecture and design flow. testable mathematical relationship between the master key and the round keys, which allows for locating possible AES key Virtex-6 FPGA and 24GB of on-board SDRAM memory. The schedules in decayed memory images and for reconstructing server uses two 6-core (12 threads) X5650 CPUs running at the original schedule by exploiting redundancies. 2.67GHz and provides 48GB RAM. For providing fast I/O the server is equipped with 3 SSDs in RAID0 configuration. w 0 1 2 3 b r 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 For mapping applications to this system, Maxeler provides 0 5A 57 45 49 5F 55 4E 44 5F 56 49 45 52 5A 49 47 MaxCompiler [8] which offers a Java API for specifying 1 E5 6C E5 49 BA 39 AB 0D 2 round 1 data flow engines (DFE) that process data streams. Since the 3 specified data path follows a restricted feed-forward data flow 4 XOR model, MaxCompiler can automatically perform optimizations 5 like buffer size optimization, pipelining and retiming, which re- 6 7 sults in very efficient implementations. Each DFE is comprised 8 round 10 of two parts, one or several kernels that implement the data- 9 90 66 20 B3 path and a manager that orchestrates the flow of data between 10 BF 96 99 15 2F F0 B9 A6 kernels, off-chip memory, and CPUs. MaxCompiler transforms the kernel and manager code into a hardware design which Fig. 1. AES key expansion: simple XOR operation for all but the first word in each round (w: word, b: byte, r: round). is further processed by the FPGA vendor tools to generate a bitfile. Additionally, MaxCompiler generates a dedicated library for controlling and configuring the kernel execution w 0 1 2 3 b r 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 from the host application. 0 5A 57 45 49 5F 55 4E 44 5F 56 49 45 52 5A 49 47 round 1 1 E5 6C E5 49 III. IDENTIFYING AES KEYS 2 RCON 3 In this section we present the approach and implementation 4 XOR XOR 5 of our hardware accelerator for searching AES key schedules, rotate substitute 6 based on the algorithm proposed by Halderman et al. [3]. 7 SBOX 8 A. Approach 9 58 A0 6A AE 90 66 20 B3 round 10 10 5D 17 07 CE The key search procedure iterates over all possible candi- Fig. 2. AES key expansion: complex operation for first word in each round.
Load more

Recommended publications
  • Revention of Coldboot Attack on Linux Systems Measures to Prevent Coldboot Attack
    Special Issue - 2017 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 ICIATE - 2017 Conference Proceedings Prevention of Coldboot Attack on Linux Systems Measures to Prevent Coldboot Attack Siddhesh Patil Ekta Patel Nutan Dhange Information Technology, Atharva Information Technology, Atharva Assistant Professor College of Engineering College of Engineering Information Technology, Atharva Mumbai University Mumbai University College of Engineering Mumbai, India Mumbai, India Mumbai University Mumbai, India Abstract— Contrary to the popular belief, DDR type RAM boot attack techniques. We implement measures to ensure that data modules retain stored memory even after power is cut off. stays secure on system shutdown. Data security is critical for most Provided physical access to the cryptosystem, a hacker or a of the business and even home computer users. RAM is used to store forensic specialist can retrieve information stored in the RAM non-persistent information into it. When an application is in use, by installing it on another system and booting from a USB drive user-specific or application-specific data may be stored in RAM. to take a RAM dump. With adequate disassembly and analytic This data can be sensitive information like client information, tools, this information stored in the RAM dump can be payment details, personal files, bank account details, etc. All this deciphered. Hackers thrive on such special-case attack information, if fallen into wrong hands, can be potentially techniques to gain access to systems with sensitive information. dangerous. The goal of most unethical hackers / attackers is to An unencrypted RAM module will contain the decryption key disrupt the services and to steal information.
    [Show full text]
  • CIS 4360 Secure Computer Systems Attacks Against Boot And
    CIS 4360 Secure Computer Systems Attacks against Boot and RAM Professor Qiang Zeng Spring 2017 Previous Class • BIOS-MBR: Generation I system boot – What BIOS and MBR are? – How does it boot the system? // Jumping to MBR – How does multi-boot work? // Chain-loading • The limitations of BIOS and MBR – Disk, memory, file system, multi-booting, security, … • UEFI-GPT: Generation II system boot – What UEFI and GPT are? – How does it boot the system? // UEFI boot manager – How does multi-boot work? // separate dirs in ESP CIS 4360 – Secure Computer Systems 2 Limitations of BIOS-MBR • MBR is very limited – Support ~2TB disk only – 4 primary partitions at most (so four OSes at most) – A MBR can store only one boot loader • BIOS is very restrictive – 16-bit processor mode; 1MB memory space (little spare space to accommodate a file system driver) – Blindly executes whatever code on MBR CIS 4360 – Secure Computer Systems 3 UEFI vs. BIOS • Disk partitioning schemes – GPT (GUID Partition Table): part of UEFI spec.; to replace MBR – MBR supports disk size 232 x 512B = 2TB, while UEFI supports much larger disks (264 x 512B ＝ 8,000,000,000 TB) – MBR supports 4 partitions, while GPT supports 128 • Memory space – BIOS: 20-bit addressing; UEFI: 32-bit or 64-bit • Pre-OS environment – BIOS only provides raw disk access, while UEFI supports the FAT file system (so you can use file names to read files) • Booting – BIOS supports boot through boot sectors (MBR and VBR) – UEFI provides a boot partition of hundreds of megabytes (and boot manager and secure boot) CIS 4360 – Secure Computer Systems 4 Previous Class How does dual-boo-ng of Linux and Windows work in UEFI-GPT? Each vendor has a separate directory storing its own boot loader code and configuraon files in the ESP (EFI System Par--on).
    [Show full text]
  • Low-Cost Mitigation Against Cold Boot Attacks for an Authentication Token
    Low-cost Mitigation against Cold Boot Attacks for an Authentication Token Ian Goldberg?1, Graeme Jenkinson2, and Frank Stajano2 1 University of Waterloo (Canada) 2 University of Cambridge (United Kingdom) Abstract. Hardware tokens for user authentication need a secure and usable mechanism to lock them when not in use. The Pico academic project proposes an authentication token unlocked by the proximity of simpler wearable devices that provide shares of the token’s master key. This method, however, is vulnera- ble to a cold boot attack: an adversary who captures a running Pico could extract the master key from its RAM and steal all of the user’s credentials. We present a cryptographic countermeasure—bivariate secret sharing—that protects all the credentials except the one in use at that time, even if the token is captured while it is on. Remarkably, our key storage costs for the wearables that supply the cryp- tographic shares are very modest (256 bits) and remain constant even if the token holds thousands of credentials. Although bivariate secret sharing has been used before in slightly different ways, our scheme is leaner and more efficient and achieves a new property—cold boot protection. We validated the efficacy of our design by implementing it on a commercial Bluetooth Low Energy development board and measuring its latency and energy consumption. For reasonable choices of latency and security parameters, a standard CR2032 button-cell battery can power our prototype for 5–7 months, and we demonstrate a simple enhancement that could make the same battery last for over 9 months.
    [Show full text]
  • On the Practicability of Cold Boot Attacks
    On the Practicability of Cold Boot Attacks Michael Gruhn and Tilo Muller¨ Friedrich-Alexander-Universitat¨ Erlangen-Nurnberg,¨ Germany fmichael.gruhn,[email protected] Abstract—Even though a target machine uses full disk The memory controller refreshes each cell’s voltage encryption, cold boot attacks can retrieve unencrypted data before it decays to the point where the bit information gets from RAM. Cold boot attacks are based on the remanence lost. Normally, the refresh rate is so high that each cell gets effect of RAM which says that memory contents do not disappear immediately after power is cut, but that they fade refreshed several times per second. However, the decay gradually over time. This effect can be exploited by rebooting of capacitors is longer than the time between two refresh a running machine, or by transplanting its RAM chips into operations of the memory controller. This can be observed an analysis machine that reads out what is left in memory. as the remanence effect, which lasts long enough that data In theory, this kind of attack is known since the 1990s. in memory survives a system reboot. This observation However, only in 2008, Halderman et al. have shown that cold boot attacks can be well deployed in practical scenarios. prompted so-called cold boot attacks. In the work in hand, we investigate the practicability of Cold boot attacks can make use of the property that cold boot attacks. We verify the claims by Halderman et al. the remanence effect is prolonged by cooling down RAM independently in a systematic fashion.
    [Show full text]
  • Mitigation of Cold Boot Attack Using an Encrypted Memory Controller IIIT
    Mitigation of Cold Boot Attack Using an Encrypted Memory Controller Student Name: Preet Kaur Walia IIIT-D-MTech-ECE-VLSI-14-16 July 10, 2016 Indraprastha Institute of Information Technology New Delhi Advisor Mohammad S. Hashmi Submitted in partial fulfillment of the requirements for the Degree of M.Tech. in Electronics and Communication, with specialization in VLSI and Embedded Systems c 2016 Preet Kaur All rights reserved Certificate This is to certify that the thesis titled “Mitigation of Cold Boot Attack Using an En- crypted Memory Controller" submitted by Preet Kaur Walia for the partial fulfillment of the requirements for the degree of Master of Technology in VLSI & Embedded Systems is a record of the bonafide work carried out by him under my guidance and supervision in the Se- curity and Privacy group at Indraprastha Institute of Information Technology, Delhi.This work has not been submitted anywhere else for the reward of any other degree. Dr. Mohammad S. Hashmi Indraprastha Institute of Information Technology, New Delhi i Abstract RAMs which are widely used in PCs and laptops are likely to break the popular supposition that data in them is lost whenever power supply is cut down. It has been proved in 2008 by a group of researchers that RAMs are no longer volatile in nature. The data remanence behaviour of DRAMs have allowed to retrieve memory contents when the power has been switched off by an attack known as cold boot attack. In cold boot attack, memory can be frozen using a refrigerant and then removed from the computer. It is then quickly placed into a specially designed system that reads out its content, targeting encryption keys and other sensitive information.
    [Show full text]
  • Physical Security Attacks on Windows Vista, © 2008 SEC Consult Unternehmensberatung Gmbh
    Physical Security Attacks on Windows Vista, © 2008 SEC Consult Unternehmensberatung GmbH PHYSICAL SECURITY ATTACKS ON WINDOWS VISTA Peter Panholzer SEC Consult Vulnerability Lab, Vienna, 03/05/2008 There are several attacks known today which leverage physical access to fully patched systems to read or patch system memory. One of them is the Cold Boot Attack (1), which allows copying the system memory after the system has been powered off and extracting the keys of encrypted harddisks from it. Another technique known for years now is the copying and manipulation of memory using firewire which, among other things, also can be used to retrieve encryption keys. Several papers describe the technical background of the firewire attack (2) (3). In a nutshell, it is possible to access the system memory of other nodes on a firewire bus via DMA and firewire’s addressing scheme. This works for reading as well as for writing. The only requirement on the target is a firewire interface, which most laptops and a lot of workstations have built in. Laptops without a firewire interface can be provided by an attacker with a PC Card (PCMCIA Card) which is automatically installed – even if the screen is locked. This means that even laptop computers without a firewire interface are vulnerable. It has been proven that Linux, MAC OS X and Windows XP are vulnerable to this attack. In March 2008, Adam Boileau released a tool called winlockpwn (4), which implements several attacks against Windows XP SP2. A while ago, SEC Consult has implemented its own proof of concepts for most versions of Windows.
    [Show full text]
  • Lest We Remember: Cold Boot Attacks on Encryption Keys
    Lest We Remember: Cold Boot Attacks on Encryption Keys J. Alex Halderman∗, Seth D. Schoen†, Nadia Heninger∗, William Clarkson∗, William Paul‡, Joseph A. Calandrino∗, Ariel J. Feldman∗, Jacob Appelbaum, and Edward W. Felten∗ ∗ Princeton University † Electronic Frontier Foundation ‡ Wind River Systems 17th USENIX Security Symposium 2008 Jan Kleine Seminar: Computer Architecture Jan Kleine | 30.10.2019 | 1 Background & Problem Novelty Key Ideas & Findings Mechanisms & Implementation Results Proposed Solutions Conclusion Strengths & Weaknesses Follow-up Work Discussion Jan Kleine | 30.10.2019 | 2 A little refresh on DRAM § A DRAM cell stores data in a capacitor § Capacitor is charged to store data § Capacitor loses charge over time § Ground state might be Vcc or Ground § Refresh (typically every 64ms) Jan Kleine | 30.10.2019 | 3 Problem § DRAM retains data longer than refresh time § Even after power loss, data is not lost right away § Data survives several seconds § RAM is the place for sensitive data § Private secrets like encryption keys § Potential for attacks on encryption keys and other sensitive data Attacker can image memory and extract data after power loss Jan Kleine | 30.10.2019 | 4 Problem: Example of data retention Jan Kleine | 30.10.2019 | 5 Background & Problem Novelty Key Ideas & Findings Mechanisms & Implementation Results Proposed Solutions Conclusion Strengths & Weaknesses Follow-up Work Discussion Jan Kleine | 30.10.2019 | 6 Novelty § First paper to demonstrate this attack vector of data retention § Demonstration on off-the-shelf
    [Show full text]
  • New Methods for Preventing Cold Boot Attacks on Encryption Keys
    Braving the Cold: New Methods for Preventing Cold Boot Attacks on Encryption Keys Patrick McGregor, Ph.D. Tim Hollebeek Alex Volynkin, Ph.D. Matthew White BitArmor Systems, Inc. COPYRIGHT © 2008 BITARMOR SYSTEMS, INC. ALL RIGHTS RESERVED. 1 Outline Who cares about Full Disk Encryption, anyway? The anatomy of a Cold Boot Attack New software‐based methods for defense – Tidy up at power down time – Built‐in temperature monitoring – Taking advantage of default BIOS behavior – Efficient virtual compartmentalization Thoughts for the future COPYRIGHT © 2008 BITARMOR SYSTEMS, INC. ALL RIGHTS RESERVED. 2 What is Full Disk Encryption (FDE)? Encrypts every bit of data on a disk or disk volume – Mostly used to encrypt laptop drives – Uses standard algorithms, e.g., AES, Triple DES User authentication used to decrypt disk keys – Some use different keys for different partitions In real time, sectors of a disk are read/written without impacting the user – The keys are stored persistently in memory to ensure high performance COPYRIGHT © 2008 BITARMOR SYSTEMS, INC. ALL RIGHTS RESERVED. 3 FDE: Why Do People Buy This Stuff? To mitigate risk – Lowers chance losing data, being sued, being fined – Data breaches can cost between $90 and $305 per record exposed – Average cost: $4.8 million per company per incident Compliance – Industry government regulations say certain data has to be encrypted • PCI DSS, OMB M‐06‐16, others Avoiding breach notification requirements – Laws in at least 39 states force disclosure of incidents – Encryption is a “get out of jail free” card COPYRIGHT © 2008 BITARMOR SYSTEMS, INC. ALL RIGHTS RESERVED. 4 User Work Patterns Can Increase Risks BitArmor survey of 250 business users – More than 40% of users leave laptops in sleep or hibernation mode when traveling – No difference between techie users and business users! Desktops matter too! – Cold boot attacks apply to any PC type – Desktops in screen lock mode are vulnerable COPYRIGHT © 2008 BITARMOR SYSTEMS, INC.
    [Show full text]
  • Is Information on Secure Hard Disk Drive Only Yours?
    IS INFORMATION ON SECURE HARD DISK DRIVE ONLY YOURS? Jakub Arm Doctoral Degree Programme (4), FEEC BUT E-mail: [email protected] Supervised by: Zdenek Bradac E-mail: [email protected] Abstract: This paper focuses on security of information saved on hard disk drives using encryption. The posibilities of information protection are outlined. Security of using AES cipher algorithm is discussed and some possible attacks are described. Regarding these attacks, some of them are serious threat, for instance, side channel attacks. Some possibilities how to avoid these attacks are demon- strated. Cipher filesystem, as the file cipher tool, is also presented. Among them, EncFS is introduced in greater detail and its use on cloud server is pointed out. Keywords: Security, hard disk drive, encryption, decryption, AES, cold boot attack, EncFS 1 INTRODUCTION The present is sometimes called informational age. This is caused by rising value of good information. Some companies deal only with information. So they need to keep their valuable information secured. Almost every computer is connected to the internet to the global network, which the information can be got from or which the information can be stolen through. Information stored on hard disk drive can be stolen also locally by physical access to the computer. So user passwords, unique ideas or projects saved on user hard disk drives are in danger. To protect information on hard drives, the content of the drive can be encrypted. That means making information impossible to read. There are three approaches to do this. First, the entire hard disk drive or disk partition can be encrypted by specific software or by hardware coprocessor built in disk drive.
    [Show full text]
  • Digital Forensics
    Advanced Security for Systems Engineering – VO 08: Digital Forensics Clemens Hlauschek, Christian Brem INSO – Industrial Software Institute of Information Systems Engineering | Faculty of Informatics | TU Wien Contents Forensics – Anti-Forensics Political/Historical Context: End-to-end Encryption Forensic Science Acquire-Analyze-Present Cryptographic Attacks and Limitations Common Attacks against Crypto Analysis of Encypted Traffic Disk encryption Advanced Security for Systems Engineering WS20 | Forensics 2 / 37 Forensics – Anti-Forensics Advanced Security for Systems Engineering WS20 | Forensics 3 / 37 End-to-end Encryption Debate ■ Australia passes Assistance & Access Act (December 2018): allows to secretly compel companies and individuals to re-engineer IT Systems for spying ■ EU Council agrees on e-Evidence proposal (December 2018): access data ■ FBI vs Apple encryption dispute (2016) ■ NSA/Snowden (2013): Dual EC DRBG backdoor, etc ■ Crypto War: Crypto export restrictions (until 1996), Clipper Chip, weak SSL keys, PGP, A5/1 Advanced Security for Systems Engineering WS20 | Forensics 4 / 37 CLEAR Proposal and Technial Discussion Secure access to encrypted storage for 3rd parties without risiking mass surveillance abuse? ■ Ray Ozzie (2018): CLEAR Proposal: Key escrow, per-device key pair for encrypting passcode, acess to device and vendor request necessary, secure hardware to ‘brick’ phone: forensic r/o lock mode. ■ Savage: Lawful Device Access without Mass Surveillance Risk (CCS’18): self-escrow of access credentials in secure time-vaulting
    [Show full text]
  • Cold Boot Key Recovery by Solving Polynomial Systems with Noise
    Cold Boot Key Recovery by Solving Polynomial Systems with Noise Martin Albrecht? and Carlos Cid 1 INRIA, Paris-Rocquencourt Center, SALSA Project UPMC Univ Paris 06, UMR 7606, LIP6, F-75005, Paris, France CNRS, UMR 7606, LIP6, F-75005, Paris, France [email protected] 2 Information Security Group, Royal Holloway, University of London Egham, Surrey TW20 0EX, United Kingdom [email protected] Abstract. A method for extracting cryptographic key material from DRAM used in modern computers has been recently proposed in [9]; the technique was called Cold Boot attacks. When considering block ciphers, such as the AES and DES, simple algorithms were also proposed in [9] to recover the cryptographic key from the observed set of round subkeys in memory (computed via the cipher's key schedule operation), which were however subject to errors due to memory bits decay. In this work we extend this analysis to consider key recovery for other ciphers used in Full Disk Encryption (FDE) products. Our algorithms are also based on closest code word decoding methods, however apply a novel method for solving a set of non-linear algebraic equations with noise based on Integer Programming. This method should have further applications in cryptology, and is likely to be of independent interest. We demonstrate the viability of the Integer Programming method by applying it against the Serpent block cipher, which has a much more complex key schedule than AES. Furthermore, we also consider the Twofish key schedule, to which we apply a dedicated method of recovery. 1 Introduction The structure of block cipher key schedules has received much renewed atten- tion, since the recent publication of high-profile attacks against the AES [4] and Kasumi [3] in the related-key model.
    [Show full text]
  • Recovering AES Keys with a Deep Cold Boot Attack
    Recovering AES Keys with a Deep Cold Boot Attack Itamar Zimerman * 1 Eliya Nachmani * 1 2 Lior Wolf 1 Abstract key by exploiting the memory leakage and the redundancy of the key expansion function used by the encryption method. Cold boot attacks inspect the corrupted random access memory soon after the power has been This attack is well-known, and defense methods for it have shut down. While most of the bits have been been heavily researched (Ooi & Kam, 2009). Vulnerable de- corrupted, many bits, at random locations, have vices include computers and smartphones (CBT,a;b;M uller¨ not. Since the keys in many encryption schemes et al., 2012; CBT,c;d). Examples of encryption systems are being expanded in memory into longer keys that have been broken by this attack include Microsoft’s with fixed redundancies, the keys can often be BitLocker, Apple’s FileVault, Linux’s Dm-crypt, TrueCrypt, restored. In this work, we combine a novel cryp- Google’s Android’s disk encryption, and many others. tographic variant of a deep error correcting code The data remanence phenomena are often modeled in one of technique with a modified SAT solver scheme two ways: a theoretical model and a more practical one. In to apply the attack on AES keys. Even though both models, there is a tendency of decaying the bit values AES consists of Rijndael S-box elements, that are to the ground state, which can be 0 or 1. For simplicity, we specifically designed to be resistant to linear and assume that 0 is the ground state.
    [Show full text]