SHRINCS: an efficient hash-based signature scheme for Bitcoin (first draft)

The SHRINCS Working Group has introduced a draft for a new cryptographic Bitcoin Improvement Proposal (BIP), which presents SHRINCS, a semi-stateful hash-based signature scheme. This draft is still in its prototype stage and should not be used in production environments as it requires comprehensive peer review and completion of formal security proofs. The draft can be accessed on GitHub at SHRINCS.md.

SHRINCS is designed to offer several advantages, including compactness with public keys sized at 48 bytes and signatures that range from 548 bytes to 5777 bytes depending on whether they are stateful or stateless. It provides security approximations aligned with NIST-I standards, using truncated SHA256 believed to be secure against post-quantum threats. Notably, the verification of SHRINCS signatures is significantly faster, approximately 4x-16x quicker than BIP340 Schnorr signatures, depending on the availability of SHA256 hardware acceleration.

However, the scheme also has certain limitations. Its stateful nature requires management software capable of handling an incrementing state counter, which tracks the number of signatures made. Mismanagement of this counter could lead to security vulnerabilities, such as signature forgery if the same state counter is reused inadvertently. Additionally, key generation and signing processes are computationally demanding, though these may be mitigated somewhat through various technical enhancements like SIMD, parallelism, or hardware acceleration.

Significant updates have been made to the original SHRINCS proposals by Jonas Nick and Mikhail Kudinov, including improved interoperability with non-Bitcoin systems through black-box compatibility with SLH-DSA algorithms and more flexible parameter sets that support higher-frequency signing needs, essential for applications like the Lightning Network.

Currently, the SHRINCS proposal does not include essential components such as test vectors, unit tests, security proofs, or optimized implementations and does not comply with Mediawiki or Markdown formats. The community's feedback is sought to refine SHRINCS' design, parameters, and cryptography to ensure security, correctness, consistency, and clarity.

This call for review is part of an ongoing effort to develop and improve blockchain technology's security infrastructure, and the SHRINCS team is open to insights and discussions that could further enhance the proposal. They have also provided an interactive tool for exploring different parameter sets and encourage engagement from the community to discuss and understand the implications of various choices in the design of semi-stateful signing schemes. For those interested in a deeper dive into the workings of SHRINCS, a video interview is available at this link.