This research introduces ElGUE (ElGamal-based Updatable Encryption), a novel asymmetric cryptographic scheme designed to address secure key rotation challenges in modern digital systems. Unlike traditional methods, which require decrypting and re-encrypting entire datasets, ElGUE allows ciphertexts encrypted under previous keys to be securely updated to new keys without decryption, ensuring continuous data confidentiality. ElGUE combines the ElGamal cryptosystem's mathematical robustness with three key features: asymmetric encryption within a public-key framework, ciphertext-independence, and unbounded key rotation depth. The scheme incorporates lightweight pseudorandom generators for efficient management and offers strong forward and backward security, protecting against both past and future key compromises. Performance evaluations show significant improvements over existing methods, with encryption and ciphertext updates completing in 0.0054 and 0.006 seconds, respectively. The scheme's security is analyzed under the Decisional Diffie-Hellman assumption, proving resistance against adaptive chosen-ciphertext attacks and information leakage. ElGUE provides an efficient, secure solution for frequent key rotations, ideal for cloud storage, IoT, secure communication networks, and regulatory-compliant systems.

KEYWORDS: Updatable Encryption ElGamal Cryptosystem Key Rotation Asymmetric Cryptography Discrete Logarithm Problem Forward Secrecy Backward Secrecy Ciphertext Independence Cryptographic Security Data Confidentiality Cloud Security Key Management Pseudorandom Generators DDH Assumption Information Security.