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Equihash

This is an optimized C++ implementation of Equihash, the memory-hard Proof-of-Work with fast verification. Equihash is designed by Alex Biryukov and Dmitry Khovratovich, cryptographers at the University of Luxembourg.

Equihash is an asymmetric proof-of-work algorithm based on a computationally hard generalized birthday problem, which requires a lot of memory to generate a proof, but is instant to verify. Equihash is adapted as the PoW in Zcash a public implementation of the cryptocurrency protocol Zerocash. It is possible to use Equihash in TLS as a client puzzle.

Equihash has two parameters: N (width in bits) and K (length), which determine the complexity of the underlying problem and thus the memory and time complexity of the Equihash PoW. The underlying hash function is Blake2b, but any collision-resistant hash function would work too.

The time complexity is proportional to K2^{N/(K+1)}, and memory complexity to 2^{K+N/(K+1)}. The proof size is 2^{K}(1+N/(K+1))+192 bits. Verification requires 2^K hashes and XORs.

Please report bugs as issues on this repository.

Recommended parameters (N,K)

For cryptocurrencies: (100/110/120,4), (108/114/120/126,5).

For client puzzles: (60/70/80/90,4), (90/96/102,5).

Usage

make builds the executable equihash.

Command-line utility

equihash is a command-line utility to test specific Equihash instances on your system. To show usage instructions, run ./equihash without arguments as

Usage:  ./equihash -n N -k K -s Seed
Parameters:
        N               The width (number of bits) of the generalized birthday problem, integer divisible by (K+1) 
        K               The length of the generalized birthday problem, small integer
        Seed            Seed for the problem, to distinguish between solutions. Integer.

For example, to compute Equihash using N=120 and k=5, consuming at least 32 MB of RAM

$ ./equihash -n 120 -k 5 -s 3

Alternative implementations

Zcash by @str4d

Intellectual property

The license is GPL-compatible.