  Technological advancements of Blockchain and other Distributed Ledger
Techniques (DLTs) promise to provide significant advantages to applications
seeking transparency, redundancy, and accountability. Actual adoption of these
emerging technologies requires incorporating cost-effective, fast, QoS-enabled,
secure, and scalable design. With the recent advent of quantum computing, the
security of current blockchain cryptosystems can be compromised to a greater
extent. Quantum algorithms like Shor's large integer factorization algorithm
and Grover's unstructured database search algorithm can provide exponential and
quadratic speedup, respectively, in contrast to their classical counterpart.
This can put threats on both public-key cryptosystems and hash functions, which
necessarily demands to migrate from classical cryptography to quantum-secure
cryptography. Moreover, the computational latency of blockchain platforms
causes slow transaction speed, so quantum computing principles might provide
significant speedup and scalability in transaction processing and accelerating
the mining process. For such purpose, this article first studies current and
future classical state-of-the-art blockchain scalability and security
primitives. The relevant quantum-safe blockchain cryptosystem initiatives which
have been taken by Bitcoin, Ethereum, Corda, etc. are stated and compared with
respect to key sizes, hash length, execution time, computational overhead, and
energy efficiency. Post Quantum Cryptographic algorithms like Code-based,
Lattice-based, Multivariate-based, and other schemes are not well suited for
classical blockchain technology due to several disadvantages in practical
implementation. Decryption latency, massive consumption of computational
resources, and increased key size are few challenges that can hinder blockchain
performance.
