Review of Encryption Techniques: A Comprehensive Survey of Classical, Symmetric, Asymmetric, Homomorphic, Blockchain-Integrated, and Post-Quantum Cryptographic Methods

Encryption is the cornerstone of modern information security, enabling confidential communication across digital infrastructures that span personal devices, enterprise networks, cloud platforms, distributed ledgers, and the Internet of Things. This article provides a structured, in-depth review of encryption techniques documented in twenty-eight authoritative sources. Coverage spans symmetric algorithms (AES, DES, 3DES, Blowfish, RC4), asymmetric methods (RSA, ECC, ElGamal), classical information-theoretically secure ciphers (One-Time Pad), hybrid encryption systems, homomorphic encryption, blockchain, searchable encryption, and post-quantum cryptographic approaches based on lattice problems, code-based assumptions, and hash functions. For each technique, this review examines theoretical foundations, algorithmic structure, operational workflow, practical implementations, computational trade-offs, and security properties under both classical and quantum threat models. Structural process diagrams are provided to illustrate how plaintext is transformed to ciphertext and back under each paradigm. The following metrics were covered during the analysis Recommendations were made on what the best applicable solution across security level, key size, throughput, and quantum resistance demonstrates that no single algorithm universally satisfies all competing demands; hybrid and lattice-based designs represent the most promising directions for future-proof encryption. Open challenges including Fully Homomorphic Encryption (FHE) performance, post-quantum migration, IoT key management, and regulatory alignment are discussed, followed by a research agenda for the post-quantum era.