This chapter deals with post-quantum cryptography (PQC) whose algorithms and protocols have been designed and implemented to protect sensitive and confidential data against attacks or cracks with quantum computers. Using Shor’s algorithm on a large-enough quantum computer or high-performance cloud, a malicious attacker could cryptanalyze any Public Key Cryptosystems like RSA/ECC public key and generate fake or duplicate digital signatures in a millisecond. NIST is making a lot of efforts to standardize PQC algorithms through competitions. Further, Quantum Key Distribution (QKD) using the BB84 protocol has been designed and developed for applications. Let us take up a new topic like proxy signature scheme which has been explored in this chapter. A quantum secure ID-based cryptographic encryption based on group rings is proven secure to use over conventional crypto encryption algorithms. The existing world faces several digital information breaches due to weak utilization of confidentiality preserving techniques. In this regard, a novel digital contents privacy scheme based on the quantum harmonic oscillator and Schrodinger paradox has been studied.