Demystifying Cryptography behind Blockchains and a Vision for Post-Quantum Blockchains

One of the backbone technology of Blockchains is cryptography. In simpler terms cryptography is the mathematical art of secret writing, however it's applications are not limited to writing secret codes only. Essentially cryptography is used to achieve three main security goals namely confidentiality (in-formation must be hidden from the unintended users), integrity (information must be prevented from illicit modifications) and availability (information must be readily available to intended users at all times). In cryptography confidentiality is achieved by employing a technique called as Encryption, integrity is achieved by employing special one way functions called as Cryptographic Hash Functions and authentication (process for verifying identity of the sender) is achieved by employing a technique called as Digital Signatures. For better understanding about the working of Blockchain it is essential to understand cryptographic concepts on which Blockchain is built. This paper presents the brief overview of such cryptographic concepts. In particular this papers throws light on the cryptographic concepts used to build Bitcoin and Ethereum Blockchains. Furthermore this paper also throws light on the need and requirements of post-quantum cryptographic primitives for post-quantum Blockchains.