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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.

IDmerkle-tree
Plain meaning

Plain meaning

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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.

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Compressed state, proofs, and scale-oriented storage patterns.

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Merkle Tree (merkle-tree)
Category: ZK Compression
Definition: 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.
Related: Merkle Proof, State Compression
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Branch

Merkle Proof

A Merkle proof is the minimal set of sibling node hashes (the proof path) along the branch from a specific leaf to the tree root, allowing anyone to independently verify that a given leaf is part of a Merkle tree by recomputing the root from the leaf hash and the sibling hashes without needing any other tree data. In Solana's state compression, every compressed account or compressed NFT interaction requires the caller to supply a valid Merkle proof; the on-chain program hashes the proof against the current root stored in the Concurrent Merkle Tree account to confirm inclusion before executing the state change. Proof size scales linearly with tree depth (e.g., a depth-20 tree requires up to 20 sibling hashes, each 32 bytes), so the canopy is used to pre-store upper-level nodes on-chain to reduce the proof data that must be passed in transactions.

Concurrent Merkle Tree
Open term
Branch

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.

Compressed NFT (cNFT)ZK Compression
Open term
Next concepts to explore

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ZK Compression

Merkle Proof

A Merkle proof is the minimal set of sibling node hashes (the proof path) along the branch from a specific leaf to the tree root, allowing anyone to independently verify that a given leaf is part of a Merkle tree by recomputing the root from the leaf hash and the sibling hashes without needing any other tree data. In Solana's state compression, every compressed account or compressed NFT interaction requires the caller to supply a valid Merkle proof; the on-chain program hashes the proof against the current root stored in the Concurrent Merkle Tree account to confirm inclusion before executing the state change. Proof size scales linearly with tree depth (e.g., a depth-20 tree requires up to 20 sibling hashes, each 32 bytes), so the canopy is used to pre-store upper-level nodes on-chain to reduce the proof data that must be passed in transactions.

Open term
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

Nullifier

A nullifier is a cryptographic value derived deterministically from a compressed account's leaf hash (and optionally a secret) that is published and recorded on-chain when that compressed account is consumed (spent) in a state transition, permanently marking the account as used and preventing it from being spent a second time in a double-spend attack. In Light Protocol, nullifiers are inserted into an on-chain nullifier queue account and periodically batch-processed by Forester nodes into a nullifier set stored in a separate Merkle tree, allowing the validity proof to assert both that the input account exists (inclusion proof) and that its nullifier has not yet been recorded (non-membership proof). The nullifier scheme allows compressed accounts to be treated as UTXOs — each account is consumed once and replaced by one or more output accounts — while maintaining the privacy and succinctness properties of the ZK proof system.

Open term
ZK Compression

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
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ZK Compressionconcurrent-merkle-tree

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.

AliasCMT
Open term
ZK Compressionmerkle-proof

Merkle Proof

A Merkle proof is the minimal set of sibling node hashes (the proof path) along the branch from a specific leaf to the tree root, allowing anyone to independently verify that a given leaf is part of a Merkle tree by recomputing the root from the leaf hash and the sibling hashes without needing any other tree data. In Solana's state compression, every compressed account or compressed NFT interaction requires the caller to supply a valid Merkle proof; the on-chain program hashes the proof against the current root stored in the Concurrent Merkle Tree account to confirm inclusion before executing the state change. Proof size scales linearly with tree depth (e.g., a depth-20 tree requires up to 20 sibling hashes, each 32 bytes), so the canopy is used to pre-store upper-level nodes on-chain to reduce the proof data that must be passed in transactions.

Open term
ZK Compressioncanopy

Canopy (Merkle Tree)

The canopy is an optional on-chain cache of the upper N levels of a Concurrent Merkle Tree's nodes, stored within the CMT account itself, which eliminates the need for clients to pass those N levels as part of their Merkle proof in transactions, thereby reducing transaction size and cost. A canopy of depth D means the top D levels of the tree (2^D - 1 nodes) are always available on-chain; for a depth-20 tree with a canopy of 14, clients only need to supply 6 sibling hashes rather than 20, saving approximately 448 bytes of transaction data per instruction. Storing a deeper canopy increases the CMT account's rent-exempt balance linearly but makes interactions cheaper in compute units and transaction space, so selecting the optimal canopy depth is a cost trade-off for tree designers.

Open term
Related terms

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ZK Compressionmerkle-proof

Merkle Proof

A Merkle proof is the minimal set of sibling node hashes (the proof path) along the branch from a specific leaf to the tree root, allowing anyone to independently verify that a given leaf is part of a Merkle tree by recomputing the root from the leaf hash and the sibling hashes without needing any other tree data. In Solana's state compression, every compressed account or compressed NFT interaction requires the caller to supply a valid Merkle proof; the on-chain program hashes the proof against the current root stored in the Concurrent Merkle Tree account to confirm inclusion before executing the state change. Proof size scales linearly with tree depth (e.g., a depth-20 tree requires up to 20 sibling hashes, each 32 bytes), so the canopy is used to pre-store upper-level nodes on-chain to reduce the proof data that must be passed in transactions.

Open term
ZK Compressionstate-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
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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

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