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Poseidon is a cryptographic hash function designed specifically for efficiency inside zero-knowledge proof arithmetic circuits (ZK-friendly), operating natively over prime fields (specifically the BN254 scalar field used by Groth16) with dramatically fewer constraints per hash than binary-oriented functions like SHA-256, which requires roughly 25,000 R1CS constraints per invocation versus Poseidon's roughly 240. In Solana's ZK Compression and state compression ecosystem, Poseidon is used as the hash function for building Merkle trees whose roots are verified inside ZK circuits, because ZK proofs must encode every hash operation as arithmetic constraints and SHA-256's bitwise operations are prohibitively expensive in this model. Solana's SVM exposes a native Poseidon syscall so on-chain programs can compute Poseidon hashes efficiently without paying the compute cost of a pure BPF implementation.

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Poseidon Hash (poseidon-hash)
Category: ZK Compression
Definition: Poseidon is a cryptographic hash function designed specifically for efficiency inside zero-knowledge proof arithmetic circuits (ZK-friendly), operating natively over prime fields (specifically the BN254 scalar field used by Groth16) with dramatically fewer constraints per hash than binary-oriented functions like SHA-256, which requires roughly 25,000 R1CS constraints per invocation versus Poseidon's roughly 240. In Solana's ZK Compression and state compression ecosystem, Poseidon is used as the hash function for building Merkle trees whose roots are verified inside ZK circuits, because ZK proofs must encode every hash operation as arithmetic constraints and SHA-256's bitwise operations are prohibitively expensive in this model. Solana's SVM exposes a native Poseidon syscall so on-chain programs can compute Poseidon hashes efficiently without paying the compute cost of a pure BPF implementation.
Related: Zero-Knowledge Proofs (ZKP), Merkle Tree

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Zero-Knowledge Proofs (ZKP)

A zero-knowledge proof is a cryptographic protocol by which a prover convinces a verifier that a statement is true — for example, that a state transition is valid — without revealing any information beyond the truth of the statement itself, satisfying the properties of completeness, soundness, and zero-knowledge. In Solana's ecosystem, ZKPs are used by ZK Compression (via Groth16 SNARKs) to prove correct state transitions for compressed accounts without storing full account state on-chain, and by the Token-2022 Confidential Transfers extension (via ElGamal encryption and range proofs) to prove token balances are non-negative without revealing the actual amounts. Solana's BPF VM exposes the alt_bn128 elliptic curve syscall to make on-chain Groth16 proof verification computationally feasible within the 1.4M compute unit budget.

Groth16 PLONK

Open term

Branch

Merkle Tree

A Merkle tree is a binary hash tree in which every leaf node contains a cryptographic hash of a data block, and every non-leaf (internal) node contains the hash of its two children, such that the single root hash cryptographically commits to the entire dataset and any modification to any leaf produces a detectably different root. In Solana, Merkle trees underpin state compression: the SPL Account Compression program maintains Concurrent Merkle Trees on-chain with only the root hash persisted in account storage, while all leaf data is derivable from transaction logs. The Poseidon hash function is preferred over SHA-256 for ZK-friendly Merkle trees because it is algebraically efficient inside arithmetic circuits used for zero-knowledge proof generation.

Merkle Proof State Compression

Open term

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ZK Compression

Zero-Knowledge Proofs (ZKP)

A zero-knowledge proof is a cryptographic protocol by which a prover convinces a verifier that a statement is true — for example, that a state transition is valid — without revealing any information beyond the truth of the statement itself, satisfying the properties of completeness, soundness, and zero-knowledge. In Solana's ecosystem, ZKPs are used by ZK Compression (via Groth16 SNARKs) to prove correct state transitions for compressed accounts without storing full account state on-chain, and by the Token-2022 Confidential Transfers extension (via ElGamal encryption and range proofs) to prove token balances are non-negative without revealing the actual amounts. Solana's BPF VM exposes the alt_bn128 elliptic curve syscall to make on-chain Groth16 proof verification computationally feasible within the 1.4M compute unit budget.

Open term

ZK Compression

Merkle Tree

A Merkle tree is a binary hash tree in which every leaf node contains a cryptographic hash of a data block, and every non-leaf (internal) node contains the hash of its two children, such that the single root hash cryptographically commits to the entire dataset and any modification to any leaf produces a detectably different root. In Solana, Merkle trees underpin state compression: the SPL Account Compression program maintains Concurrent Merkle Trees on-chain with only the root hash persisted in account storage, while all leaf data is derivable from transaction logs. The Poseidon hash function is preferred over SHA-256 for ZK-friendly Merkle trees because it is algebraically efficient inside arithmetic circuits used for zero-knowledge proof generation.

Open term

ZK Compression

Proof Aggregation

Technique of combining multiple zero-knowledge proofs into a single, compact proof that can be verified more efficiently than verifying each proof individually. Reduces on-chain verification costs by batching proofs. Used in ZK compression systems to batch-verify multiple state transitions in a single verification step on Solana.

Open term

ZK Compression

PLONK

PLONK (Permutations over Lagrange-bases for Oecumenical Noninteractive arguments of Knowledge) is a universal zk-SNARK proving system that requires only a single, circuit-agnostic trusted setup (a universal SRS), eliminating the need for per-circuit ceremonies required by systems like Groth16, while producing proofs that are slightly larger but allow circuits to be updated or added without new ceremonies. PLONK-based systems (including its variants Turbo-PLONK and Ultra-PLONK used by protocols like Aztec) support custom gates and lookup tables, enabling more efficient encoding of operations like range checks and hash functions in arithmetic circuits. On Solana, PLONK is less commonly deployed for on-chain verification than Groth16 because verification is more compute-intensive, but it is used off-chain in toolchains and protocol designs targeting future SVM upgrades with broader syscall support.

Open term

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ZK Compressionzk-proofs

Zero-Knowledge Proofs (ZKP)

A zero-knowledge proof is a cryptographic protocol by which a prover convinces a verifier that a statement is true — for example, that a state transition is valid — without revealing any information beyond the truth of the statement itself, satisfying the properties of completeness, soundness, and zero-knowledge. In Solana's ecosystem, ZKPs are used by ZK Compression (via Groth16 SNARKs) to prove correct state transitions for compressed accounts without storing full account state on-chain, and by the Token-2022 Confidential Transfers extension (via ElGamal encryption and range proofs) to prove token balances are non-negative without revealing the actual amounts. Solana's BPF VM exposes the alt_bn128 elliptic curve syscall to make on-chain Groth16 proof verification computationally feasible within the 1.4M compute unit budget.

Open term

ZK Compressionmerkle-tree

Merkle Tree

A Merkle tree is a binary hash tree in which every leaf node contains a cryptographic hash of a data block, and every non-leaf (internal) node contains the hash of its two children, such that the single root hash cryptographically commits to the entire dataset and any modification to any leaf produces a detectably different root. In Solana, Merkle trees underpin state compression: the SPL Account Compression program maintains Concurrent Merkle Trees on-chain with only the root hash persisted in account storage, while all leaf data is derivable from transaction logs. The Poseidon hash function is preferred over SHA-256 for ZK-friendly Merkle trees because it is algebraically efficient inside arithmetic circuits used for zero-knowledge proof generation.

Open term

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ZK Compression

State Compression

State Compression is Solana's technique for storing the cryptographic fingerprint (root hash) of a Merkle tree on-chain while keeping the actual leaf data off-chain in the Solana ledger's account data logs, reducing the cost of storing large datasets by orders of magnitude. A compressed NFT collection of 1 million items costs roughly 50 SOL to mint versus ~12,000 SOL with standard SPL accounts, because only a single Concurrent Merkle Tree account occupies on-chain storage. Any data change requires updating the root hash and supplying a Merkle proof to the on-chain program, which verifies inclusion without reading the full dataset.

Open term

ZK Compression

ZK Compression, pioneered by Light Protocol, extends Solana's state compression model beyond NFTs to general-purpose compressed accounts by using zero-knowledge proofs (specifically Groth16 SNARKs verified via the alt_bn128 syscall) to prove the validity of state transitions without storing full account state on-chain. Compressed accounts live in on-chain Merkle trees but their data is reconstructed from the Solana ledger by indexers like Photon, enabling developers to build applications that use thousands of accounts at a fraction of the normal rent cost — often 1,000x to 5,000x cheaper than regular accounts. The protocol introduces compressed tokens, compressed PDAs, and a system of nullifiers to prevent double-spends while maintaining Solana's throughput.

Open term

ZK Compression

Compressed Account

A compressed account is a Solana account whose state is stored as a leaf in an on-chain Concurrent Merkle Tree rather than as a dedicated on-chain account, making it 100–1,000x cheaper to create and maintain because no rent-exempt lamport balance is required per account. Compressed accounts are identified by a hash of their data and position in the tree; to interact with one, a client must supply a Merkle proof (or rely on the canopy) showing the leaf is part of the current tree root, which the on-chain program verifies before processing the state change. Light Protocol's compressed account model supports arbitrary data, discriminators, and owner programs, making it a general-purpose replacement for expensive on-chain accounts in high-volume use cases.

Open term

ZK Compression

Concurrent Merkle Tree

A Concurrent Merkle Tree (CMT) is a specialized on-chain Solana data structure that allows multiple state updates to the same Merkle tree within a single block without conflicting, by recording a changelog buffer of recent root transitions that validators use to reconcile parallel proof submissions. A CMT is parameterized by its maximum depth (max_depth, determining tree capacity of 2^max_depth leaves), max_buffer_size (number of concurrent changes the changelog can track, directly controlling how many operations per slot the tree can safely absorb), and an optional canopy_depth. The SPL Account Compression program manages CMTs, and they are the foundational storage primitive for both Metaplex compressed NFTs and Light Protocol compressed accounts.

Open term