Matryoshka: Hiding Secret Communication in Plain Sight

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Billions of people now have conversations daily over the Internet. A large portion of this communication takes place via secure messaging protocols that offer "end-to-end encryption'" guarantees and resilience to compromise like the widely-used Double Ratc ...

Since the advent of internet and mass communication, two public-key cryptographic algorithms have shared the monopoly of data encryption and authentication: Diffie-Hellman and RSA. However, in the last few years, progress made in quantum physics -- and mo ...

With the looming threat of large-scale quantum computers, a fair portion of recent cryptographic research has focused on examining cryptographic primitives from the perspective of a quantum adversary. Shor's 1994 result revealed that quantum computers can ...

In this dissertation, we propose multiple methods to improve transfer learning for pretrained language models (PLMs). Broadly, transfer learning is a powerful technique in natural language processing, where a language model is first pre-trained on a data-r ...

Recent transformer language models achieve outstanding results in many natural language processing (NLP) tasks. However, their enormous size often makes them impractical on memory-constrained devices, requiring practitioners to compress them to smaller net ...

To mitigate state exposure threats to long-lived instant messaging sessions, ratcheting was introduced, which is used in practice in protocols like Signal. However, existing ratcheting protocols generally come with a high cost. Recently, Caforio et al. pro ...

Messaging between two parties and in the group setting has enjoyed widespread attention both in practice, and, more recently, from the cryptographic community. One of the main challenges in the area is constructing secure (end-to- end encrypted) and effici ...

Internet blackouts are challenging environments for anonymity and censorship resistance. Existing popular anonymity networks (e.g., Freenet, I2P, Tor) rely on Internet connectivity to function, making them impracticable during such blackouts. In such a set ...

The beginning of 21st century provided us with many answers about how to reach the channel capacity. Polarization and spatial coupling are two techniques for achieving the capacity of binary memoryless symmetric channels under low-complexity decoding algor ...

Most communication systems (e.g., e-mails, instant messengers, VPNs) use encryption to prevent third parties from learning sensitive information. However, encrypted communications protect the contents but often leak metadata: the amount of data sent and th ...

Recently, cryptographic literature has seen new block cipher designs such as PRESENT, GIFT or SKINNY that aim to be more lightweight than the current standard, i.e., AES. Even though AES family of block ciphers were designed two decades ago, they still rem ...

We consider the problem of secret key generation from correlated Gaussian random variables in the finite blocklength regime. Such keys could be used to encrypt communication in IoT networks, and have provable secrecy guarantees in contrast to classic crypt ...

Time travel has always been a fascinating topic in literature and physics. In cryptography, one may wonder how to keep data confidential for some time. In this dissertation, we will study how to make private information travel to the future. This dissertat ...

Following up mass surveillance and privacy issues, modern secure communication protocols now seek strong security, such as forward secrecy and post-compromise security, in the face of state exposures. To address this problem, ratcheting was thereby introdu ...

After ratcheting attracted attention mostly due to practical real-world protocols, recently a line of work studied ratcheting as a primitive from a theoretic point of view. Literature in this line, pursuing the strongest security of ratcheting one can hope ...

We present the design and implementation of SafetyPin, a system for encrypted mobile-device backups. Like existing cloud-based mobile-backup systems, including those of Apple and Google, SafetyPin requires users to remember only a short PIN and defends aga ...

The bit-sliding paper of Jean et al. (CHES 2017) showed that the smallest-size circuit for SPN based block ciphers such as AES, SKINNY and PRESENT can be achieved via bit-serial implementations. Their technique decreases the bit size of the datapath and na ...

The implementation of the AES encryption core by Moradi et al. at Eurocrypt 2011 is one of the smallest in terms of gate area. The circuit takes around 2400 gates and operates on an 8 bit datapath. However this is an encryption only core and unable to cate ...

Multimedia contents are inherently sensitive signals that must be protected when processed in untrusted environments. The field of Secure Signal Processing addresses this challenge by developing methods which enable operating with sensitive signals in a pr ...

Many post-quantum cryptosystems which have been proposed in the National Institute of Standards and Technology (NISI) standardization process follow the same meta-algorithm, but in different algebras or different encoding methods. They usually propose two ...

Matryoshka: Hiding Secret Communication in Plain Sight

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On the Theory and Practice of Modern Secure Messaging

Secure and Efficient Cryptographic Algorithms in a Quantum World

Security in the Presence of Quantum Adversaries

Improving Generalization of Pretrained Language Models

Revisiting Offline Compression: Going Beyond Factorization-based Methods for Transformer Language Models

Optimal Symmetric Ratcheting for Secure Communication

Analysis and Improvements of the Sender Keys Protocol for Group Messaging

Moby: A Blackout-Resistant Anonymity Network for Mobile Devices

Symmetry in design and decoding of polar-like codes

Analyzing and Protecting Communication Metadata

Six shades lighter: a bit-serial implementation of the AES family

On Polar Coding For Finite Blocklength Secret Key Generation Over Wireless Channels

Time in cryptography

Symmetric Asynchronous Ratcheted Communication with Associated Data

Determining the Core Primitive for Optimally Secure Ratcheting

SafetyPin: Encrypted Backups with Human-Memorable Secrets

The Area-Latency Symbiosis: Towards Improved Serial Encryption Circuits

Compact Circuits for Combined AES Encryption/Decryption

Revisiting Multivariate Lattices for Encrypted Signal Processing

Misuse Attacks on Post-quantum Cryptosystems