Beyond Modes: Building a Secure Record Protocol from a Cryptographic Sponge Permutation

Abstract. BLINKER is a light-weight cryptographic suite and record protocol built from a single permutation. Its design is based on the Sponge construction used by the SHA-3 algorithm KECCAK. We examine the SpongeWrap authen-ticated encryption mode and expand its padding mechanism to offer explicit do-main separation and enhanced security for our specific requirements: shared se-cret half-duplex keying, encryption, and a MAC-and-continue mode. We motivate these enhancements by showing that unlike legacy protocols, the resulting record protocol is secure against a two-channel synchronization attack while also having a significantly smaller implementation footprint. The design facilitates security proofs directly from a single cryptographic primitive (a single security assump-tion) rather than via idealization of multitude of algorithms, paddings and modes of operation. The protocol is also uniquely suitable for an autonomous or semi-autonomous hardware implementation of protocols where the secrets never leave the module, making it attractive for smart card and HSM designs

TEDT, a Leakage-Resilient AEAD mode for High (Physical) Security Applications

We propose TEDT, a new Authenticated Encryption with Associated Data (AEAD) mode leveraging Tweakable Block Ciphers (TBCs). TEDT provides the following features: (i) It offers asymptotically optimal security in the multi-user setting. (ii) It offers nonce misuse-resilience, that is, the repetition of nonces does not impact the security of ciphertexts produced with fresh nonces. (iii) It offers KDM security in the multi-user setting, that is, its security is maintained even if key-dependent messages are encrypted. (iv) It offers full leakage-resilience, that is, it limits the exploitability of physical leakages via side-channel attacks, even if these leakages happen during every message encryption and decryption operation. (v) It can be implemented with a remarkably low energy cost when strong resistance to side-channel attacks is needed, supports online encryption and handles static & incremental associated data efficiently. Concretely, TEDT encourages leveled implementations, in which two TBCs are implemented: one needs strong and energy demanding protections against side-channel attacks but is used in a limited way, while the other only requires weak and energy efficient protections and performs the bulk of the computation. As a result, TEDT leads to considerably more energy efficient implementations compared to traditional AEAD schemes, whose side-channel security requires to uniformly protect every (T)BC execution

Efficient Implementation of IEEE 802.11i Wi-Fi Security (WPA2-PSK) Standard Using FPGA

The rationale behind the thesis was to design efficient implementations of cryptography algorithms used for Wi-Fi Security as per IEEE 802.11i Wi-Fi Security (WPA2-PSK) standard. The focus was on software implementation of Password-Based Key Derivation Function 2 (PBKDF2) using Keyed-Hash Message Authentication Code (HMAC)-SHA1, which is used for authentication, and, hardware implementation of AES-256 cipher, which is used for data confidentiality. In this thesis, PBKDF2 based on HMAC-SHA1 was implemented on software using C programming language, and, AES-256 was implemented on hardware using Verilog HDL. The overall implementation was designed and tested on Nexys4 FPGA board. The performance of the implementation was compared with other existing designs. Latency (us) was used as the performance metric for PBKDF2, whereas, throughput (Gb/s), resource utilization (Number of Slices), efficiency (Kb/s per slice) and latency (ns) were used as performance metrics for AES-256. MRF24WG0MA PMOD Wi-Fi module was the 2.4 GHz Wi-Fi module which was interfaced with Nexys4 FPGA board for wireless communication. When the correct security credentials were entered in the implemented system interfaced to the Wi-Fi module, it was successfully authenticated by a 2.4 GHz wireless router (or mobile hotspot) configured to work in WPA2-PSK security mode. Once this system was authenticated, the implemented AES-256 cipher within the system was used to provide a layer of encryption over the data being communicated in the network

On the Post-Quantum Security of Classical Authenticated Encryption Schemes

We study the post-quantum security of authenticated encryption (AE) schemes, designed with classical security in mind. Under superposition attacks, many CBC-MAC variants have been broken, and AE modes employing those variants, such as EAX and GCM, thus fail at authenticity. As we show, the same modes are IND-qCPA insecure, i.e., they fail to provide privacy under superposition attacks. However, a constrained version of GCM is IND-qCPA secure, and a nonce-based variant of the CBC-MAC is secure under superposition queries. Further, the combination of classical authenticity and classical chosen-plaintext privacy thwarts attacks with superposition chosen-ciphertext and classical chosen-plaintext queries -a security notion that we refer to as IND-qdCCA. And nonce-based key derivation allows generically turning an IND-qdCCA secure scheme into an IND-qCCA secure scheme

Analysis and Design of Authentication and Encryption Algorithms for Secure Cloud Systems

Along with the fast growth of networks and mobile devices, cloud computing has become one of the most attractive and effective technologies and business solutions nowadays. Increasing numbers of organizations and customers are migrating their businesses and data to the cloud due to the flexibility and cost-efficiency of cloud systems. Preventing unauthorized access of sensitive data in the cloud has been one of the biggest challenges when designing a secure cloud system, and it strongly relies on the chosen authentication and encryption algorithms for providing authenticity and confidentiality, respectively. This thesis investigates various aspects of authentication and encryption algorithms for securing cloud systems, including authenticated encryption modes of operation, block ciphers, password hashing algorithms, and password-less/two-factor authentication mechanisms. Improving Authenticated Encryption Modes. The Galois/Counter Mode (GCM) is an authenticated encryption mode of operation for block ciphers. It has been widely adopted by many network standards and protocols that protect the security of cloud communications, such as TLS v1.2, IEEE 802.1AE and IPsec. Iwata et al. recently found a flaw in GCM's original proofs for non-96-bit nonce cases, and then presented new security bounds for GCM. The new bounds imply that the success probabilities of adversaries for attacking GCM are much larger than the originally expected ones. We propose a simple change to repair GCM. When applied, it will improve the security bounds by a factor of about $2^{20}$ while maintaining most of the original proofs. Analyzing Polynomial-Based Message Authentication Codes. We investigate attacks on polynomial-based message authentication code (MAC) schemes including the one adopted in GCM. We demonstrate that constructing successful forgeries of these MAC schemes does not necessarily require hash collisions. This discovery removes certain restrictions in the attacks previously proposed by Procter and Cid. Moreover, utilizing a special design of GCM for processing non-96-bit nonces, we turn these forgery attacks into birthday attacks, which will significantly increase their success probabilities. Therefore, by considering the birthday attacks and the security proof flaw found by Iwata et al., cloud system designers should avoid using GCM with non-96-bit nonces if they do not revise the design of GCM. Analyzing Block Ciphers. We propose a new framework for analyzing symmetric-key ciphers by guessing intermediate states to divide ciphers into small components. This framework is suitable for lightweight ciphers with simple key schedules and block sizes smaller than key lengths. Using this framework, we design new attacks on the block cipher family KATAN. These attacks can recover the master keys of 175-round KATAN32, 130-round KATAN48 and 112-round KATAN64 faster than exhaustive search, and thus reach many more rounds than the existing attacks. We also provide new attacks on 115-round KATAN32 and 100-round KATAN48 in order to demonstrate that this new kind of attack can be more time-efficient and memory-efficient than the existing ones. Designing Password Hashing Algorithms. Securely storing passwords and deriving cryptographic keys from passwords are also crucial for most secure cloud system designs. However, choices of well-studied password hashing algorithms are extremely limited, as their security requirements and design principles are different from common cryptographic primitives. We propose two practical password hashing algorithms, Pleco and Plectron. They are built upon well-understood cryptographic algorithms, and combine the advantages of symmetric-key and asymmetric-key primitives. By employing the Rabin cryptosystem, we prove that the one-wayness of Pleco is at least as strong as the hard problem of integer factorization. In addition, both password hashing algorithms are designed to be sequential memory-hard, in order to thwart large-scale password searching using parallel hardware, such as GPUs, FPGAs, and ASICs. Designing Password-less/Two-Factor Authentication Mechanisms. Motivated by a number of recent industry initiatives, we propose Loxin, an innovative solution for password-less authentication for cloud systems and web applications. Loxin aims to improve on passwords with respect to both usability and security. It utilizes push message services for mobile devices to initiate authentication transactions based on asymmetric-key cryptography, and enables users to access multiple services by using pre-owned identities, such as email addresses. In particular, the Loxin server cannot generate users' authentication credentials, thereby eliminating the potential risk of credential leakage if the Loxin server gets compromised. Furthermore, Loxin is fully compatible with existing password-based authentication systems, and thus can serve as a two-factor authentication mechanism

Authenticated Encryption for Very Short Inputs

We study authenticated encryption (AE) modes dedicated to very short messages, which are crucial for Internet-of-things applications. Since the existing general-purpose AE modes need at least three block cipher calls for non-empty messages, we explore the design space for AE modes that use at most two calls. We proposed a family of AE modes, dubbed Manx, that work when the total input length is less than $2n$ bits, using an $n$-bit block cipher. Notably, the second construction of Manx can encrypt almost n-bit plaintext and saves one or two block cipher calls from the standard modes, such as GCM or OCB, keeping the comparable provable security. We also present benchmarks on popular 8/32-bit microprocessors using AES. Our results show the clear advantage of Manx over the previous modes for such short messages

Triplex: an Efficient and One-Pass Leakage-Resistant Mode of Operation

This paper introduces and analyzes Triplex, a leakage-resistant mode of operation based on Tweakable Block Ciphers (TBCs) with 2n-bit tweaks. Triplex enjoys beyond-birthday ciphertext integrity in the presence of encryption and decryption leakage in a liberal model where all intermediate computations are leaked in full and only two TBC calls operating a long-term secret are protected with implementationlevel countermeasures. It provides beyond-birthday confidentiality guarantees without leakage, and standard confidentiality guarantees with leakage for a single-pass mode embedding a re-keying process for the bulk of its computations (i.e., birthday confidentiality with encryption leakage under a bounded leakage assumption). Triplex improves leakage-resistant modes of operation relying on TBCs with n-bit tweaks when instantiated with large-tweak TBCs like Deoxys-TBC (a CAESAR competition laureate) or Skinny (used by the Romulus finalist of the NIST lightweight crypto competition). Its security guarantees are maintained in the multi-user setting

Analysis Design & Applications of Cryptographic Building Blocks

This thesis deals with the basic design and rigorous analysis of cryptographic schemes and primitives, especially of authenticated encryption schemes, hash functions, and password-hashing schemes. In the last decade, security issues such as the PS3 jailbreak demonstrate that common security notions are rather restrictive, and it seems that they do not model the real world adequately. As a result, in the first part of this work, we introduce a less restrictive security model that is closer to reality. In this model it turned out that existing (on-line) authenticated encryption schemes cannot longer beconsidered secure, i.e. they can guarantee neither data privacy nor data integrity. Therefore, we present two novel authenticated encryption scheme, namely COFFE and McOE, which are not only secure in the standard model but also reasonably secure in our generalized security model, i.e. both preserve full data inegrity. In addition, McOE preserves a resonable level of data privacy. The second part of this thesis starts with proposing the hash function Twister-Pi, a revised version of the accepted SHA-3 candidate Twister. We not only fixed all known security issues of Twister, but also increased the overall soundness of our hash-function design. Furthermore, we present some fundamental groundwork in the area of password-hashing schemes. This research was mainly inspired by the medial omnipresence of password-leakage incidences. We show that the password-hashing scheme scrypt is vulnerable against cache-timing attacks due to the existence of a password-dependent memory-access pattern. Finally, we introduce Catena the first password-hashing scheme that is both memory-consuming and resistant against cache-timing attacks