Scrypt hashcash implementation for node & browsers.

npm i scrypt-hashcash

sh = require("scrypt-hashcash");

<script src="script-hashcash.min.js"></script>

API

sh.pow(text, target, [noncefunction, callback])

Generate a proof-of-work token over some text for a given target difficulty.

• text is the material to be hashed over.
• target is the difficulty vector to try to outperform (use sh.target(bits) to generate a target vector for a particular difficulty of bits zero-bits.
• noncefunction is an optional callback function to return nonces which takes a single argument i being the number of iterations so far.
• callback is an optional callback for when the promise API is not used.

sh.pow("some text", sh.target(4)).then(function(pow) {
  console.log("Nonce found:", sh.toHex(pow.nonce));
  console.log("Resulting hash:", sh.toHex(pow.hash));
  console.log("Iterations it took:", pow.iterations);
});

sh.verify(text, nonce, target, [callback])

Verify some previously found nonce hashes to a lower value than the target difficulty specified.

• text is the material which was hashed to find the nonce.
• nonce is the nonce which the client claims to have found to beat the target.
• target is the difficult vector to be verfied has having been exceeded.
• callback is an optional callback for when the promise API is not used.

sh.verify(text, nonce, target).then(function(v) {
  if (v.verified) {
    console.log("verification passed with hash " + sh.toHex(v.hash));
  } else {
    console.log("verification failed for this nonce");
  }
});

sh.target(bits)

Generate a target vector for a particular number of zero-bits.

• bits is the number of zero-bits of difficulty required.

> sh.target(4);
Uint8Array [ 15, 255, 255, 255, 255, 255, 255, 255 ]

sh.difficulty(hashrate, time)

Calculate how many bits of difficulty are required on average to run at a particular hashrate for a particular time.

• hashrate is the hashrate expected.
• time is the amount of time (e.g. seconds).

> s.difficulty(100, 10)
9

sh.measure()

Measure the number of hashes per second the current device can perform.

• iterations is an optional number of iterations to carry out (defaults to 50).

s.measure().then(function(d) {
  console.log(d + " hashes per second");
})

sh.toHex(h)

Convenience function to convert an array to a hex string representation.

sh.fromHex(h)

Convenience function to convert a hex string to a Uint8Array.

sh.config

The scrypt configuration being used. Parameters include dkLen, N, r, and p. See the Scrypt Wikipedia page for a summary of these variables and this blog post for a treatment of how to tune them for different uses.

Command line usage

You can use scrypt-hashcash from the command line.

For example, to find a collision of 4 bits against the test vector:

$ scrypt-hashcash 0:030626:adam@cypherspace.org 4
0:030626:adam@cypherspace.org:8043dfc5850f9525

Then to verify the nonce that was found and get the hash:

$ scrypt-hashcash --verify 0:030626:adam@cypherspace.org:213dc824e7eed707 4
Verified: 0120e170dead0aab

Test a bad nonce:

$ scrypt-hashcash --verify 0:030626:adam@cypherspace.org:213dc824e7eed709 4
Verification failed! Hash does not have sufficient zero bits for this nonce.
$ echo $?
2

Measure the hashes per second of the current device:

$ scrypt-hashcash --measure
79.18 hashes per second