documentation

src/keypair.js

@@ -34,6 +34,11 @@ function unpackEncryptedMessage(encryptedMessage) {
 }
 
 class Keypair {
+  /**
+   * Initialize a new keypair. Generates a random private key if not defined
+   *
+   * @param {string} privkey
+   */
   constructor(privkey = ethers.Wallet.createRandom().privateKey) {
     this.privkey = privkey
     this.pubkey = poseidonHash([this.privkey])
@@ -44,10 +49,21 @@ class Keypair {
     return toFixedHex(this.pubkey) + Buffer.from(this.encryptionKey, 'base64').toString('hex')
   }
 
+  /**
+   * Key address for this keypair, alias to {@link toString}
+   *
+   * @returns {string}
+   */
   address() {
     return this.toString()
   }
 
+  /**
+   * Initialize new keypair from address string
+   *
+   * @param str
+   * @returns {Keypair}
+   */
   static fromString(str) {
     if (str.length === 130) {
       str = str.slice(2)
@@ -62,10 +78,22 @@ class Keypair {
     })
   }
 
+  /**
+   * Encrypt data using keypair encryption key
+   *
+   * @param {Buffer} bytes
+   * @returns {string} a hex string with encrypted data
+   */
   encrypt(bytes) {
     return packEncryptedMessage(encrypt(this.encryptionKey, { data: bytes.toString('base64') }, 'x25519-xsalsa20-poly1305'))
   }
 
+  /**
+   * Decrypt data using keypair private key
+   *
+   * @param {string} data a hex string with data
+   * @returns {Buffer}
+   */
   decrypt(data) {
     return Buffer.from(decrypt(unpackEncryptedMessage(data), this.privkey.slice(2)), 'base64')
   }

src/utils.js

@@ -9,6 +9,7 @@ const poseidonHash2 = (a, b) => poseidonHash([a, b])
 const FIELD_SIZE = BigNumber.from(
   '21888242871839275222246405745257275088548364400416034343698204186575808495617',
 )
+
 /** Generate random number of specified byte length */
 const randomBN = (nbytes = 31) => BigNumber.from(crypto.randomBytes(nbytes))
 
@@ -38,6 +39,7 @@ const toFixedHex = (number, length = 32) =>
     : BigNumber.from(number).toHexString().slice(2)
   ).padStart(length * 2, '0')
 
+/** Convert value into buffer of specified byte length */
 const toBuffer = (value, length) =>
   Buffer.from(
     BigNumber.from(value)

src/utxo.js

@@ -1,16 +1,28 @@
 const { ethers } = require('hardhat')
 const { BigNumber } = ethers
-const { randomBN, poseidonHash } = require('./utils')
+const { randomBN, poseidonHash, toBuffer } = require('./utils')
 const Keypair = require('./keypair')
 
 class Utxo {
-  constructor({ amount = 0, keypair = new Keypair(), blinding = randomBN(), index } = {}) {
+  /**
+   *
+   * @param {BigNumber | BigInt | number | string} amount UTXO amount
+   * @param {BigNumber | BigInt | number | string} blinding Blinding factor
+   * @param {Keypair} keypair
+   * @param {number|null} index UTXO index in the merkle tree
+   */
+  constructor({ amount = 0, keypair = new Keypair(), blinding = randomBN(), index = null} = {}) {
     this.amount = BigNumber.from(amount)
     this.blinding = BigNumber.from(blinding)
     this.keypair = keypair
     this.index = index
   }
 
+  /**
+   * Returns commitment for this UTXO
+   *
+   * @returns {BigNumber}
+   */
   getCommitment() {
     if (!this._commitment) {
       this._commitment = poseidonHash([this.amount, this.blinding, this.keypair.pubkey])
@@ -18,6 +30,11 @@ class Utxo {
     return this._commitment
   }
 
+  /**
+   * Returns nullifier for this UTXO
+   *
+   * @returns {BigNumber}
+   */
   getNullifier() {
     if (!this._nullifier) {
       if (this.amount > 0 && (this.index === undefined || this.keypair.privkey === undefined || this.keypair.privkey === null)) {
@@ -28,18 +45,24 @@ class Utxo {
     return this._nullifier
   }
 
+  /**
+   * Encrypt UTXO data using the current keypair
+   *
+   * @returns {string} `0x`-prefixed hex string with data
+   */
   encrypt() {
-    const blindingBuf = Buffer.from(this.blinding.toHexString().slice(2), 'hex')
+    const bytes = Buffer.concat([toBuffer(this.blinding, 31), toBuffer(this.amount, 31)])
-    const amountBuf = Buffer.from(this.amount.toHexString().slice(2), 'hex')
-    const bytes = Buffer.concat([
-      Buffer.alloc(31 - blindingBuf.length),
-      blindingBuf,
-      Buffer.alloc(31 - amountBuf.length),
-      amountBuf,
-    ])
     return this.keypair.encrypt(bytes)
   }
 
+  /**
+   * Decrypt a UTXO
+   *
+   * @param {Keypair} keypair keypair used to decrypt
+   * @param {string} data hex string with data
+   * @param {number} index UTXO index in merkle tree
+   * @returns {Utxo}
+   */
   static decrypt(keypair, data, index) {
     const buf = keypair.decrypt(data)
     return new Utxo({

test/full.test.js

@@ -8,8 +8,6 @@ const {
   toFixedHex,
   takeSnapshot,
   revertSnapshot,
-  packEncryptedMessage,
-  unpackEncryptedMessage,
 } = require('../src/utils')
 const Utxo = require('../src/utxo')