Blockchain transactions are decentralized, secure, and transparent, and they have altered industries. However, the emergence of quantum computing presents a severe security risk to the traditional encryption algorithms used in blockchain. Post-quantum signatures are required to preserve integrity and reliability. Furthermore, combining the InterPlanetary File System (IPFS) with blockchain provides a long-term strategy for data storage and sharing. This study investigates the integration of post-quantum signatures with the IPFS in a blockchain system, which can considerably enhance blockchain system efficiency. We increase security and efficiency by recording hash values of signatures and public keys within the blockchain and storing their actual content using the IPFS. The study compares NIST-recommended post-quantum signatures with the ECDSA in a Bitcoin exchange scheme to show how effective the system is in countering quantum threats while maintaining optimal performance. This research makes an important addition to the long-term viability and dependability of blockchain technology in the face of the growing landscape of quantum computing breakthroughs.

Digital signatures are unsuitable for specific applications that are sensitive on a personal or commercial level because they are universally verifiable. Jakobsson et al. proposed the Designated Verifier Signature (DVS) system, which only allows the intended verifier to validate a message’s signature. It prohibits the disclosure of a conviction to a third party. This functionality is useful in applications that require both authenticity and signer privacy, such as electronic voting and tender calls. The vast majority of current DVS schemes are based on difficult number theory problems such as integer factorization or discrete log problems over various groups. The development of a large-scale quantum computer would render these schemes unsafe. As a result, it is critical to develop quantum-resistant DVS methods. In both quantum and classical computers, signatures based on one-way functions are more efficient and secure. They have several advantages over digital signatures based on trapdoor functions. As a result, hash-based signatures are now considered viable alternatives to number-theoretic signatures. Existing hash-based signatures, on the other hand, are easily verifiable by anyone. As a result, they do not protect the signer’s identity. In addition, they are one-time signatures. This paper presents a hash-based multi-time designated verifier signature scheme that ensures signer anonymity. The unforgeability of the signature scheme is also tested in the random oracle model under chosen message attack. The properties such as non-transferability and non-delegatability are investigated.

As a standard digital signature may be verified by anybody, it is unsuitable for personal or economically sensitive applications. The chameleon signature system was presented by Krawczyk and Rabin as a solution to this problem. It is based on a hash then sign model. The chameleon hash function enables the trapdoor information holder to compute a message digest collision. The holder of a chameleon signature is the recipient of a chameleon signature. He could compute collision on the hash value using the trapdoor information. This keeps the recipient from disclosing his conviction to a third party and ensures the privacy of the signature. The majority of the extant chameleon signature methods are built on the computationally infeasible number theory problems, like integer factorization and discrete log. Unfortunately, the construction of quantum computers would be rendered insecure to those schemes. This creates a solid requirement for construct chameleon signatures for the quantum world. Hence, this paper proposes a novel quantum secure chameleon signature scheme based on hash functions. As a hash-based cryptosystem is an essential candidate of a post-quantum cryptosystem, the proposed hash-based chameleon signature scheme would be a promising alternative to the number of theoretic-based methods. Furthermore, the proposed method is key exposure-free and satisfies the security requirements such as semantic security, non-transferability, and unforgeability.

Chameleon signatures introduced by Krawczyk and Rabin are based on well-established hash-and-sign paradigm. It is a non-interactive signature scheme that simultaneously provides the properties of non-transferability and non-repudiation. The chameleon hash function is a trapdoor one-way function which prevents everyone except the holder of the trapdoor information from computing collision on a message digest. The chameleon signature scheme achieves non-transferability as the recipient of the signature is the holder of the trapdoor information. He could be able to compute collision on the hash value and hence no third party could be able to identify the real signer. In the initial constructions of chameleon signature schemes, the occurrences of collisions expose the secret key of the recipient. This strongly prevents the recipient to compute hash collisions, partially undermining the concept of non-transferability. Hence it is important to overcome this key exposure problem, and its aligned problems of key revocation and key redistribution. Also the existing chameleon signature schemes are based on the hard problems in number theory such as integer factorization or the discrete log problem over various groups. The construction of a large-scale quantum computer would render insecurity to these schemes. Hence as recommended by NISTIR 8105, we propose a quantum resistant chameleon hashing and signature scheme based on hard problems in coding theory. The scheme also satisfies the security properties of chameleon signature, such as collision resistance, semantic security, key exposure freeness, non-transferability and unforgeability. As code-based cryptosystem is an important candidate of postquantum cryptosystem, the proposed code-based chameleon signature scheme would be a promising alternative to the number theoretic based schemes. In addition, we also propose a method to transform the code-based chameleon hashing scheme into an ordinary signature scheme and prove its unforgeability in the random oracle model.