Blockchain algorithms for security are designed to strengthen the resilience, confidentiality, and trustworthiness of blockchain systems while addressing potential vulnerabilities in decentralized environments. Research in this domain focuses on consensus mechanisms like Proof of Work (PoW), Proof of Stake (PoS), Byzantine Fault Tolerance (BFT), and their improved variants that ensure secure agreement among distributed nodes even in the presence of malicious actors. Studies also explore cryptographic techniques such as zero-knowledge proofs, homomorphic encryption, hash-based algorithms, and digital signatures that safeguard transaction privacy, data integrity, and user authentication. In addition, algorithmic models for intrusion detection, anomaly monitoring, and secure smart contract execution are investigated to protect against evolving cyber threats. By analyzing and enhancing these algorithms, research aims to provide scalable, efficient, and tamper-resistant blockchain architectures that ensure end-to-end security across diverse applications like finance, healthcare, IoT, and supply chain systems.