Online/Offline Digital Signatures: A Systematic Literature Review

In the rapidly evolving digital landscape, efficient cryptographic systems are increasingly critical. Digital Signature (DS) schemes are essential for ensuring data integrity and authenticity, particularly in resource-constrained environments like the Internet of Things (IoT). The Offline/Online (O/O) extension has gained attention for its effective signing process, as it allows for the precomputation of operations beforehand. Informally, in this kind of scheme, signing a message involves two phases. The first is an offline phase that requires moderate computation but can be done in advance, before the message is known. The second is an online phase that starts once the message is available, using the precomputed data to complete the signature more quickly. This survey provides the first comprehensive overview of the adaptation of O/O constructions for various resource-constrained use cases, such as IoT, low-power and mobile contexts, and other contexts, such as blockchains, where latency is a crucial metric. We reviewed 36 O/O DS schemes, focusing on trends, challenges, and applications. We examined the benefits, drawbacks, and potential areas for improvement of the reviewed O/O schemes, as well as identifying the features inherent to the O/O design. Our analysis indicates that the latter effectively mitigates issues related to expensive computations, delays, and high energy consumption, provided that the increased storage demands for offline signatures are manageable. This survey lays the groundwork for future research and development of O/O schemes, driven by the increasing prevalence of constrained environments where these schemes are particularly useful.