Poseidon is a zero-knowledge shielded transaction system built on Solana. It uses Groth16 zkSNARKs and a Merkle tree of note commitments to provide private deposits, transfers, and withdrawals. Unlike centralized privacy solutions that rely on API-based services, Poseidon is a fully decentralized on-chain program that operates trustlessly on Solana's blockchain. On-chain observers see funds entering and leaving the pool but cannot reliably link specific deposits to withdrawals.