Smart contracts are self-executing contracts deployed on blockchain networks but are prone to security attacks such as reentrancy, integer overflows, and unauthenticated access. This paper proposes a blockchain-based security framework combining MSA, ZKP, and FV to enhance smart contracts, thereby building trust and resilience. The methodology to be adopted includes identification of vulnerabilities, security protocols in place, and testing their viability on a private Ethereum test network. The experimental results depict the fact that MSA has an attack prevention rate of 98% with minimal increase in gas costs by just 12%. ZKP increases privacy with an overhead in execution time at 50 ms, and FV guarantees the detection of vulnerability before the actual deployment at 100% with the least overhead on the gas costs of 5%. To summarize, the above outcomes simply depict the effectiveness of authentication, cryptographic methodology, and formal verification for secure smart contracts. Optimization of gas efficiency and the study of hybrid security models constitute the next two phases.