Chaum’s Blind Signature

Two implementations of RSA Blind Signatures

1. ./rsablind.js
   https://en.wikipedia.org/wiki/Blind_signature

2. ./rsablind2.js
   https://github.com/arisath/Blind-RSA

The RSA key generation uses the node-only module node-rsa but everything else should work outside of node.js

Use

npm install --save blind-signatures

const BlindSignature = require('blind-signatures');
const Bob = {
  key: BlindSignature.keyGeneration({ b: 2048 }), // b: key-length
  blinded: null,
  unblinded: null,
  message: null,
};
const Alice = {
  message: 'Hello Chaum!',
  N: null,
  E: null,
  r: null,
  signed: null,
  unblinded: null,
};
// Alice wants Bob to sign a message without revealing it's contents.
// Bob can later verify he did sign the message
console.log('Message:', Alice.message);
// Alice gets N and E variables from Bob's key
Alice.N = Bob.key.keyPair.n.toString();
Alice.E = Bob.key.keyPair.e.toString();
const { blinded, r } = BlindSignature.blind({
  message: Alice.message,
  N: Alice.N,
  E: Alice.E,
}); // Alice blinds message
Alice.r = r;
// Alice sends blinded to Bob
Bob.blinded = blinded;
const signed = BlindSignature.sign({
  blinded: Bob.blinded,
  key: Bob.key,
}); // Bob signs blinded message
// Bob sends signed to Alice
Alice.signed = signed;
const unblinded = BlindSignature.unblind({
  signed: Alice.signed,
  N: Alice.N,
  r: Alice.r,
}); // Alice unblinds
Alice.unblinded = unblinded;
// Alice verifies
const result = BlindSignature.verify({
  unblinded: Alice.unblinded,
  N: Alice.N,
  E: Alice.E,
  message: Alice.message,
});
if (result) {
  console.log('Alice: Signatures verify!');
} else {
  console.log('Alice: Invalid signature');
}
// Alice sends Bob unblinded signature and original message
Bob.unblinded = Alice.unblinded;
Bob.message = Alice.message;
// Bob verifies
const result2 = BlindSignature.verify2({
  unblinded: Bob.unblinded,
  key: Bob.key,
  message: Bob.message,
});
if (result2) {
  console.log('Bob: Signatures verify!');
} else {
  console.log('Bob: Invalid signature');
}