Communicating Through Subliminal-Free Signatures

By exploiting the inherent randomness used by certain digital signature protocols, subliminal channels can subvert these protocols without degrading their security. Due to their nature, these channels cannot be easily detected by an outside observer. Therefore, they pose a severe challenge for protocol designers. More precisely, designers consider certain assumptions implicitly, but in reality these assumptions turn out to be false or cannot be enforced or verified. In this paper we exemplify exactly such a situation by presenting several subliminal channels with a small capacity in Zhang et al. and Dong et al.\u27s subliminal-free signature protocols

Subliminal Hash Channels

Due to their nature, subliminal channels are mostly regarded as being malicious, but due to recent legislation efforts users\u27 perception might change. Such channels can be used to subvert digital signature protocols without degrading the security of the underlying primitive. Thus, it is natural to find countermeasures and devise subliminal-free signatures. In this paper we discuss state-of-the-art countermeasures and introduce a generic method to bypass them

Subliminal channels in post-quantum digital signature schemes

We analyze the digital signatures schemes submitted to NIST\u27s Post-Quantum Cryptography Standardization Project in search for subliminal channels

Secure and efficient covert communication for blockchain-integrated SAGINs

Blockchain has brought great potential in improving Space-Air-Ground Integrated Networks (SAGINs) in terms of security and efficiency. In blockchain-integrated SAGINs, many applications and services inherently require both the communication contents and communication behaviors to be secure against eavesdroppers, in which a covert communication algorithm is always deployed as a fundamental communication component. However, existing covert communication schemes suffer from critical problems. On the one hand, they require a sender to locally maintain a cryptographic key for a long period of time, which is very costly and inefficient to renew which means renewing the secret key. On the other hand, the ciphertext of covertly sent data would explicitly appear in the network, and thereby the schemes are vulnerable to secret key breach. In this paper, we propose a secure and efficient covert communication scheme for blockchain-integrated SAGINs, dubbed CC-BSAGINs, to free the sender from maintaining secret keys. The key technique is to map the covertly sent data to some transactions on the underlying blockchain in a secure and efficient way; the mapping information is sent via a covert communication algorithm. Such a two-step mechanism releases the sender from key management and does not require the ciphertext to be communicated. We provide formal security proofs and conduct a comprehensive performance evaluation, which demonstrates the security and efficiency of CC-BSAGINs

Act natural! : Having a Private Chat on a Public Blockchain

Chats have become an essential means of interpersonal interaction. Yet untraceable private communication remains an elusive goal, as most messengers hide content, but not communication patterns. The knowledge of communication patterns can by itself reveal too much, as happened e.g., in the context of the Arab Spring. The subliminal channel in cryptographic systems - as introduced by Simmons in his pioneering works - enables untraceable private communication in plain sight. In this context, blockchains are a natural object for subliminal communication: accessing them is innocuous, as they rely on distributed access for verification and extension. At the same time, blockchain transactions generate hundreds of thousands transactions per day that are individually signed and placed on the blockchain. This significantly increases the availability of publicly accessible cryptographic transactions where subliminal channels can be placed. In this paper we propose a public-key subliminal channel using ECDSA signatures on blockchains and prove that our construction is undetectable in the random oracle model under a common cryptographic assumption. While our approach is applicable to any blockchain platform relying on (variants of) ECDSA signatures, we present a proof of concept of our method for the popular Bitcoin protocol and show the simplicity and practicality of our approach

The Cryptographic Strength of Tamper-Proof Hardware

Tamper-proof hardware has found its way into our everyday life in various forms, be it SIM cards, credit cards or passports. Usually, a cryptographic key is embedded in these hardware tokens that allows the execution of simple cryptographic operations, such as encryption or digital signing. The inherent security guarantees of tamper-proof hardware, however, allow more complex and diverse applications