How Aleo Uses Zero-Knowledge Proofs to Enable Privacy and Programmability on the Blockchain

Prateek Tripathi
5 min readNov 1, 2023

Blockchain technology has revolutionized the way we store, transfer, and verify data on the internet. However, most blockchain platforms face a trade-off between privacy and programmability. Privacy means that users can transact or interact without revealing their identities or sensitive information. Programmability means that users can create and execute smart contracts that define the rules and logic of their applications.

However, achieving both privacy and programmability on the blockchain is not trivial. Most public blockchains, such as Bitcoin and Ethereum, are transparent and open for anyone to see. This means that users have to sacrifice their privacy in order to use the network. On the other hand, some private blockchains, such as Zcash and Monero, are opaque and hide all the details of the transactions. This means that users have to sacrifice their programmability in order to use the network.

Is there a way to have both privacy and programmability on the blockchain? This is where Aleo comes in. Aleo is a platform for building fully private applications using zero-knowledge cryptography. It allows developers to write, run, and host decentralized applications that are scalable, cost-effective, and secure. Aleo uses zero-knowledge proofs to enable both privacy and programmability on the blockchain.

What are zero-knowledge proofs?

Zero-knowledge proofs are a cryptographic technique that allows one party (the prover) to convince another party (the verifier) that a statement is true, without revealing any information beyond the validity of the statement. For example, Alice can prove to Bob that she knows the password to a website, without revealing the password itself.

Zero-knowledge proofs have many applications in cryptography, such as authentication, encryption, digital signatures, and more. However, one of the most promising applications of zero-knowledge proofs is in blockchain technology. Zero-knowledge proofs can enable users to verify transactions or state transitions on the blockchain without revealing their inputs or outputs. This can enhance the privacy and scalability of blockchain applications.

How does Aleo use zero-knowledge proofs?

Aleo uses zero-knowledge proofs as the foundation of a system called ZEXE (Zero-Knowledge EXEcution). ZEXE is a protocol that enables users to execute state transitions offline and produce transactions that attest to their correctness. These transactions contain only a proof, not the inputs or outputs that generated it. The proof can be verified by anyone on the network in constant time, regardless of the complexity of the computation.

ZEXE has two main advantages over existing blockchain protocols. First, it provides strong privacy guarantees, as the transactions hide all information about the computation. Second, it provides high scalability, as the verification does not require re-executing the computation or accessing its data.

ZEXE consists of three main components: Leo, snarkOS, and snarkVM.

Leo

Leo is a domain-specific language (DSL) for developing zero-knowledge applications on Aleo. Leo is based on Rust and has a syntax that abstracts away the low-level details of cryptography. Leo allows developers to express their logic in a clear and concise way, without worrying about performance or security issues.

Leo supports various features that make it easy and convenient to write zero-knowledge applications, such as:

  • Types: Leo supports basic types (such as integers, booleans, arrays, etc.), custom types (such as structs and enums), and circuit types (such as fields and groups).
  • Functions: Leo supports defining and calling functions with parameters and return values.
  • Control flow: Leo supports conditional statements (such as if-else), loop statements (such as for and while), and assertions.
  • Imports: Leo supports importing external packages from the Leo Package Manager (LPM) or local files.
  • Tests: Leo supports writing unit tests and integration tests for verifying the correctness of the code.

Leo also supports compiling the code into an intermediate representation (IR) that can be used by snarkVM to generate zero-knowledge proofs.

snarkOS

snarkOS is a decentralized operating system for zero-knowledge applications. It forms the backbone of Aleo network, which verifies transactions and stores the encrypted state of applications in a publicly-verifiable manner.

snarkOS uses a novel proof-of-succinct-work (PoSW) consensus protocol that leverages zero-knowledge proofs to achieve both security and efficiency. PoSW requires miners to produce both a proof-of-work (PoW) solution and a zero-knowledge proof for each block. The PoW solution ensures that the block is valid according to the network rules. The zero-knowledge proof ensures that the block contains only valid transactions according to ZEXE protocol.

PoSW has several benefits over traditional PoW protocols, such as:

  • Security: PoSW prevents various attacks on PoW networks, such as selfish mining, double spending, and censorship.
  • Efficiency: PoSW reduces the network bandwidth and storage requirements, as the blocks contain only proofs, not data.
  • Incentives: PoSW rewards miners for both producing blocks and verifying transactions, aligning their interests with the network.

snarkOS also supports various features that enhance the user experience and developer experience of Aleo network, such as:

  • Bootnodes: snarkOS provides a set of hard-coded nodes that help new nodes to join the network and discover peers.
  • RPC: snarkOS provides a remote procedure call (RPC) interface that allows users and developers to interact with the network and perform various operations, such as querying the state, sending transactions, or mining blocks.
  • Metrics: snarkOS provides a metrics server that collects and displays various statistics about the network and the node, such as the number of peers, the block height, the hash rate, etc.

snarkVM

snarkVM is a virtual machine for zero-knowledge execution. It executes the IR generated by Leo and produces zero-knowledge proofs that can be verified by snarkOS.

snarkVM features a custom IR that enables unlimited runtime and fast proof generation. The IR is based on a rank-1 constraint system (R1CS), which is a system of linear equations that represents the computation. snarkVM uses various techniques to optimize the R1CS, such as:

  • Gadgets: snarkVM provides a library of pre-defined gadgets that implement common operations, such as arithmetic, logic, comparison, etc. Gadgets reduce the number of constraints and variables in the R1CS, improving the performance and readability of the code.
  • Synthesis: snarkVM performs a synthesis process that transforms the R1CS into a quadratic arithmetic program (QAP), which is a polynomial representation of the computation. QAP enables snarkVM to use efficient zero-knowledge proof systems, such as Groth16 or Marlin.
  • Recursion: snarkVM supports recursive proof composition, which allows verifying multiple proofs using a single proof. Recursion enables snarkVM to achieve scalability and composability for complex applications.

Conclusion

Aleo is a platform for building fully private applications using zero-knowledge cryptography. It uses zero-knowledge proofs to enable both privacy and programmability on the blockchain. Aleo consists of three main components: Leo, snarkOS, and snarkVM. Leo is a DSL for developing zero-knowledge applications. snarkOS is a decentralized operating system for zero-knowledge applications. snarkVM is a virtual machine for zero-knowledge execution.

Aleo is an innovative and ambitious project that aims to bring the power of zero-knowledge to the masses. By providing a simple, secure, and scalable platform for private applications, Aleo can unlock new possibilities and opportunities for users, developers, and enterprises.

If you are interested in learning more about Aleo or getting involved in its development, you can visit its website, documentation, GitHub, or Discord. You can also read more articles on its blog or Medium.

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Prateek Tripathi

Introducing Prateek Tripathi, a tech-savvy individual with a passion for all things crypto, blockchain, and coding.