eth-crypto

eth-crypto

Cryptographic javascript-functions for ethereum and how to use them together with web3 and solidity.

Tutorials

Creating Keys and use them for ethereum-transactions

In this tutorial we will create an ethereum-identity and use it so send transactions to the blockchain. Creating transactions.

Sign and validate data with solidity

In this tutorial we will sign data in javascript and validate the signature inside of a smart-contract. Signed Data.

Sending encrypted and signed data to other identites

In this tutorial we will use the ethereum-identites and asymmetric cryptography to send an encrypted and signed message from alice to bob. Encrypted Message.

Functions

Install

  npm install eth-crypto --save

// es6
import EthCrypto from 'eth-crypto';

// node
const EthCrypto = require('eth-crypto');

API

• createIdentity()
• publicKeyByPrivateKey()
• addressByPublicKey()
• sign()
• recover()
• recoverPublicKey()
• encryptWithPublicKey()
• decryptWithPrivateKey()
• signTransaction()
• txDataByCompiled()
• hex.compress() hex.decompress()

createIdentity()

Creates a new ethereum-identity with privateKey, publicKey and address as hex-string.

  const identity = EthCrypto.createIdentity();
  /* > {
      address: '0x3f243FdacE01Cfd9719f7359c94BA11361f32471',
      privateKey: '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07',
      publicKey: 'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'
  } */

publicKeyByPrivateKey()

Derives the publicKey from a privateKey and returns it as hex-string.

  const publicKey = EthCrypto.publicKeyByPrivateKey(
      '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07'
  );
  // > 'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'

addressByPublicKey()

Derives the ethereum-address from the publicKey.

  const address = EthCrypto.addressByPublicKey(
      'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'
  );
  // > '0x3f243FdacE01Cfd9719f7359c94BA11361f32471'

sign()

Signs the hash with the privateKey. Returns the signature as hex-string.

  const message = 'foobar';
  const messageHash = EthCrypto.hash.keccak256(message);
  const signature = EthCrypto.sign(
      '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07', // privateKey
      messageHash // hash of message
  );
  // > '0xc04b809d8f33c46ff80c44ba58e866ff0d5..'

recover()

Recovers the signers address from the signature.

    const signer = EthCrypto.recover(
      '0xc04b809d8f33c46ff80c44ba58e866ff0d5..',
      'foobar' // signed message
  );
  // > '0x3f243FdacE01Cfd9719f7359c94BA11361f32471'

recoverPublicKey()

Recovers the signers publicKey from the signature.

    const signer = EthCrypto.recover(
      '0xc04b809d8f33c46ff80c44ba58e866ff0d5..',
      'foobar' // signed message
  );
  // > 'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece..'

encryptWithPublicKey()

Encrypts the message with the publicKey so that only the corresponding privateKey can decrypt it. Returns (async) the encrypted data as object with hex-strings.

    const encrypted = await EthCrypto.encryptWithPublicKey(
        'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...', // publicKey
        'foobar' // message
    );
    /* >  {
            iv: '02aeac54cb45283b427bd1a5028552c1',
            ephemPublicKey: '044acf39ed83c304f19f41ea66615d7a6c0068d5fc48ee181f2fb1091...',
            ciphertext: '5fbbcc1a44ee19f7499dbc39cfc4ce96',
            mac: '96490b293763f49a371d3a2040a2d2cb57f246ee88958009fe3c7ef2a38264a1'
        } */

decryptWithPrivateKey()

Decrypts the encrypted data with the privateKey. Returns (async) the message as string.

    const message = await EthCrypto.decryptWithPrivateKey(
        '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07', // privateKey
        {
            iv: '02aeac54cb45283b427bd1a5028552c1',
            ephemPublicKey: '044acf39ed83c304f19f41ea66615d7a6c0068d5fc48ee181f2fb1091...',
            ciphertext: '5fbbcc1a44ee19f7499dbc39cfc4ce96',
            mac: '96490b293763f49a371d3a2040a2d2cb57f246ee88958009fe3c7ef2a38264a1'
        } // encrypted-data
    );
    // 'foobar'

signTransaction()

Signs a raw transaction with the privateKey. Returns a serialized tx which can be submitted to the node.

const identity = EthCrypto.createIdentity();
const rawTx = {
    from: identity.address,
    to: '0x86Fa049857E0209aa7D9e616F7eb3b3B78ECfdb0',
    value: 1000000000000000000,
    gasPrice: 5000000000,
    nonce: 0,
    gasLimit: 21000
};
const signedTx = EthCrypto.signTransaction(
    rawTx,
    identity.privateKey
);
console.log(signedTx);
// > '071d3a2040a2d2cb...'

// you can now send the tx to the node
const receipt = await web3.eth.sendSignedTransaction(signedTx);

txDataByCompiled()

Creates the data-string which must be submitted with an transaction to create a contract-instance.

const solc = require('solc');

// create compiled solidity-code
const compiled = solc.compile(
    'contract ExampleContract {...',
    1
).contracts[':ExampleContract'];

const createCode = EthCrypto.txDataByCompiled(
    compiled.interface, // abi
    compiled.bytecode, // bytecode
    [identity.address] // constructor-arguments
);

// now you can submit this to the blockchain
const serializedTx = EthCrypto.signTransaction(
    {
        from: identity.address,
        nonce: 0,
        gasLimit: 5000000,
        gasPrice: 5000000000,
        data: createCode
    },
    identity.privateKey
);
const receipt = await web3.eth.sendSignedTransaction(serializedTx);

hex compress/decompress

Compress or decompress a hex-string to make it smaller. You can either compress to utf16 which reduces the size to about 1/4, or to base64 which reduces the size to about 4/5.

const hexString = '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07'; // 66 chars

const utf16 = EthCrypto.hex.compress(hexString); // compress to utf16
// > 'ၻ炞䆷襞ⶬ輦ꂩቊ쮷蛰ﴚ艡Řᨇ' // 16 chars

const base64 = EthCrypto.hex.compress(hexString, true); // compress to base64
// > 'EHvpRnCeQbeJXuqfLaz5mKCpEkrLt4bw/RqCYQFYGgc=' // 44 chars

EthCrypto.hex.decompress(utf16); // decompress from utf16
// > '0x107be946709e41b7895eea9f2d...'

EthCrypto.hex.decompress(base64, true); // decompress from base64
// > '0x107be946709e41b7895eea9f2d...'