Miden Virtual Machine

A STARK-based virtual machine.

WARNING: This project is in an alpha stage. It has not been audited and may contain bugs and security flaws. This implementation is NOT ready for production use.

Overview

Miden VM is a zero-knowledge virtual machine written in Rust. For any program executed on Miden VM, a STARK-based proof of execution is automatically generated. This proof can then be used by anyone to verify that the program was executed correctly without the need for re-executing the program or even knowing the contents of the program.

• If you'd like to learn more about how Miden VM works, check out the documentation.
• If you'd like to start using Miden VM, check out the miden crate.
• If you'd like to learn more about STARKs, check out the references section.

Status and features

Miden VM is currently on release v0.9. In this release, most of the core features of the VM have been stabilized, and most of the STARK proof generation has been implemented. While we expect to keep making changes to the VM internals, the external interfaces should remain relatively stable, and we will do our best to minimize the amount of breaking changes going forward.

The next version of the VM is being developed in the next branch. There is also a documentation for the latest features and changes in the next branch documentation next branch.

Feature highlights

Miden VM is a fully-featured virtual machine. Despite being optimized for zero-knowledge proof generation, it provides all the features one would expect from a regular VM. To highlight a few:

• Flow control. Miden VM is Turing-complete and supports familiar flow control structures such as conditional statements and counter/condition-controlled loops. There are no restrictions on the maximum number of loop iterations or the depth of control flow logic.
• Procedures. Miden assembly programs can be broken into subroutines called procedures. This improves code modularity and helps reduce the size of Miden VM programs.
• Execution contexts. Miden VM program execution can span multiple isolated contexts, each with its own dedicated memory space. The contexts are separated into the root context and user contexts. The root context can be accessed from user contexts via customizable kernel calls.
• Memory. Miden VM supports read-write random-access memory. Procedures can reserve portions of global memory for easier management of local variables.
• u32 operations. Miden VM supports native operations with 32-bit unsigned integers. This includes basic arithmetic, comparison, and bitwise operations.
• Cryptographic operations. Miden assembly provides built-in instructions for computing hashes and verifying Merkle paths. These instructions use the Rescue Prime Optimized hash function (which is the native hash function of the VM).
• External libraries. Miden VM supports compiling programs against pre-defined libraries. The VM ships with one such library: Miden stdlib which adds support for such things as 64-bit unsigned integers. Developers can build other similar libraries to extend the VM's functionality in ways which fit their use cases.
• Nondeterminism. Unlike traditional virtual machines, Miden VM supports nondeterministic programming. This means a prover may do additional work outside of the VM and then provide execution hints to the VM. These hints can be used to dramatically speed up certain types of computations, as well as to supply secret inputs to the VM.
• Customizable hosts. Miden VM can be instantiated with user-defined hosts. These hosts are used to supply external data to the VM during execution/proof generation (via nondeterministic inputs) and can connect the VM to arbitrary data sources (e.g., a database or RPC calls).

Planned features

In the coming months we plan to finalize the design of the VM and implement support for the following features:

• Recursive proofs. Miden VM will soon be able to verify a proof of its own execution. This will enable infinitely recursive proofs, an extremely useful tool for real-world applications.
• Better debugging. Miden VM will provide a better debugging experience including the ability to place breakpoints, better source mapping, and more complete program analysis info.
• Faulty execution. Miden VM will support generating proofs for programs with faulty execution (a notoriously complex task in ZK context). That is, it will be possible to prove that execution of some program resulted in an error.

Compilation to WebAssembly.

Miden VM is written in pure Rust and can be compiled to WebAssembly. Rust's std standard library is enabled as feature by default for most crates. For WASM targets, one can compile with default features disabled by using --no-default-features flag.

Concurrent proof generation

When compiled with concurrent feature enabled, the prover will generate STARK proofs using multiple threads. For benefits of concurrent proof generation check out benchmarks below.

Internally, we use rayon for parallel computations. To control the number of threads used to generate a STARK proof, you can use RAYON_NUM_THREADS environment variable.

Project structure

The project is organized into several crates like so:

Performance

The benchmarks below should be viewed only as a rough guide for expected future performance. The reasons for this are twofold:

1. Not all constraints have been implemented yet, and we expect that there will be some slowdown once constraint evaluation is completed.
2. Many optimizations have not been applied yet, and we expect that there will be some speedup once we dedicate some time to performance optimizations.

Overall, we don't expect the benchmarks to change significantly, but there will definitely be some deviation from the below numbers in the future.

A few general notes on performance:

• Execution time is dominated by proof generation time. In fact, the time needed to run the program is usually under 1% of the time needed to generate the proof.
• Proof verification time is really fast. In most cases it is under 1 ms, but sometimes gets as high as 2 ms or 3 ms.
• Proof generation process is dynamically adjustable. In general, there is a trade-off between execution time, proof size, and security level (i.e. for a given security level, we can reduce proof size by increasing execution time, up to a point).
• Both proof generation and proof verification times are greatly influenced by the hash function used in the STARK protocol. In the benchmarks below, we use BLAKE3, which is a really fast hash function.

Single-core prover performance

When executed on a single CPU core, the current version of Miden VM operates at around 20 - 25 KHz. In the benchmarks below, the VM executes a Fibonacci calculator program on Apple M1 Pro CPU in a single thread. The generated proofs have a target security level of 96 bits.

As can be seen from the above, proving time roughly doubles with every doubling in the number of cycles, but proof size grows much slower.

We can also generate proofs at a higher security level. The cost of doing so is roughly doubling of proving time and roughly 40% increase in proof size. In the benchmarks below, the same Fibonacci calculator program was executed on Apple M1 Pro CPU at 128-bit target security level:

Multi-core prover performance

STARK proof generation is massively parallelizable. Thus, by taking advantage of multiple CPU cores we can dramatically reduce proof generation time. For example, when executed on an 8-core CPU (Apple M1 Pro), the current version of Miden VM operates at around 140 KHz. And when executed on a 64-core CPU (Amazon Graviton 3), the VM operates at around 250 KHz.

In the benchmarks below, the VM executes the same Fibonacci calculator program for 2²⁰ cycles at 96-bit target security level:

Recursive proofs

Proofs in the above benchmarks are generated using BLAKE3 hash function. While this hash function is very fast, it is not very efficient to execute in Miden VM. Thus, proofs generated using BLAKE3 are not well-suited for recursive proof verification. To support efficient recursive proofs, we need to use an arithmetization-friendly hash function. Miden VM natively supports Rescue Prime Optimized (RPO), which is one such hash function. One of the downsides of arithmetization-friendly hash functions is that they are considerably slower than regular hash functions.

In the benchmarks below we execute the same Fibonacci calculator program for 2²⁰ cycles at 96-bit target security level using RPO hash function instead of BLAKE3:

In the above, proof generation on some platforms can be hardware-accelerated. Specifically:

• On Apple M1/M2 platforms the built-in GPU is used for a part of proof generation process.
• On the Graviton platform, SVE vector extension is used to accelerate RPO computations.

References

Proofs of execution generated by Miden VM are based on STARKs. A STARK is a novel proof-of-computation scheme that allows you to create an efficiently verifiable proof that a computation was executed correctly. The scheme was developed by Eli Ben-Sasson, Michael Riabzev et al. at Technion - Israel Institute of Technology. STARKs do not require an initial trusted setup, and rely on very few cryptographic assumptions.

Here are some resources to learn more about STARKs:

• STARKs whitepaper: Scalable, transparent, and post-quantum secure computational integrity
• STARKs vs. SNARKs: A Cambrian Explosion of Crypto Proofs

Vitalik Buterin's blog series on zk-STARKs:

• STARKs, part 1: Proofs with Polynomials
• STARKs, part 2: Thank Goodness it's FRI-day
• STARKs, part 3: Into the Weeds

Alan Szepieniec's STARK tutorials:

• Anatomy of a STARK
• BrainSTARK

StarkWare's STARK Math blog series:

• STARK Math: The Journey Begins
• Arithmetization I
• Arithmetization II
• Low Degree Testing
• A Framework for Efficient STARKs

StarkWare's STARK tutorial:

• STARK 101

License

This project is MIT licensed.