# eth-crypto
Cryptographic javascript-functions for ethereum and tutorials on how to use them together with web3js and solidity.
## Tutorials
- **[Creating keys and use them for ethereum transactions](./tutorials/creating-transactions.md)**
In this tutorial we will create an ethereum-identity and use it to send transactions to the blockchain.
- **[Sign and validate data with solidity](./tutorials/signed-data.md)**
In this tutorial we will sign data in javascript and validate the signature inside of a smart-contract.
- **[Sending encrypted and signed data to other identities](./tutorials/encrypted-message.md)**
In this tutorial we will use the ethereum-identities and asymmetric cryptography to send an encrypted and signed message from Alice to Bob.
## Sponsored by
The JavaScript Database
## Using eth-crypto
### Install
```bash
npm install eth-crypto --save
```
```javascript
// es6
import EthCrypto from 'eth-crypto';
// node
const EthCrypto = require('eth-crypto');
```
## API
- [createIdentity()](#createidentity)
- [publicKeyByPrivateKey()](#publickeybyprivatekey)
- [publicKey.toAddress()](#publickeytoaddress)
- [publicKey.compress()](#publickeycompress)
- [publicKey.decompress()](#publickeydecompress)
- [sign()](#sign)
- [recover()](#recover)
- [recoverPublicKey()](#recoverpublickey)
- [encryptWithPublicKey()](#encryptwithpublickey)
- [decryptWithPrivateKey()](#decryptwithprivatekey)
- [cipher.stringify()](#cipherstringify)
- [cipher.parse()](#cipherparse)
- [signTransaction()](#signtransaction)
- [txDataByCompiled()](#txdatabycompiled)
- [calculateContractAddress()](#calculatecontractaddress)
- [hex.compress() hex.decompress()](#hex-compressdecompress)
### createIdentity()
Creates a new ethereum-identity with privateKey, publicKey and address as hex-string.
```javascript
const identity = EthCrypto.createIdentity();
/* > {
address: '0x3f243FdacE01Cfd9719f7359c94BA11361f32471',
privateKey: '0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07',
publicKey: 'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'
} */
```
You can also create an identity by providing your own entropy-buffer. Use this with caution, a bad entropy can result in an unsecure private key.
```javascript
const entropy = Buffer.from('f2dacf...', 'utf-8'); // must contain at least 128 chars
const identity = EthCrypto.createIdentity(entropy);
/* > {
address: '0x59c8d4d645B0a3b230DE368d815ebDE372d37Ea8',
privateKey: '0x18cea40e44624867ddfd775b2898cdb2da29b4be92ee072b9eb02d43b6f2473a',
publicKey: '991ce4643653ef452327ee3d1a56af19c84599d340ffd427e784...'
} */
```
### publicKeyByPrivateKey()
Derives the publicKey from a privateKey and returns it as hex-string.
```javascript
const publicKey = EthCrypto.publicKeyByPrivateKey(
'0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07'
);
// > 'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'
```
### publicKey.toAddress()
Derives the ethereum-address from the publicKey.
```javascript
const address = EthCrypto.publicKey.toAddress(
'bf1cc3154424dc22191941d9f4f50b063a2b663a2337e5548abea633c1d06ece...'
);
// > '0x3f243FdacE01Cfd9719f7359c94BA11361f32471'
```
### publicKey.compress()
Compresses an uncompressed publicKey.
```javascript
const address = EthCrypto.publicKey.compress(
'04a34d6aef3eb42335fb3cacb59...'
);
// > '03a34d6aef3eb42335fb3cacb59478c0b44c0bbeb8bb4ca427dbc7044157a5d24b' // compressed keys start with '02' or '03'
```
### publicKey.decompress()
Decompresses a compressed publicKey.
```javascript
const address = EthCrypto.publicKey.decompress(
'03a34d6aef3eb42335fb3c...'
);
// > 'a34d6aef3eb42335fb3cacb5947' // non-compressed keys start with '04' or no prefix
```
### sign()
Signs the hash with the privateKey. Returns the signature as hex-string.
```javascript
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.
```javascript
const signer = EthCrypto.recover(
'0xc04b809d8f33c46ff80c44ba58e866ff0d5..',
EthCrypto.hash.keccak256('foobar') // signed message hash
);
// > '0x3f243FdacE01Cfd9719f7359c94BA11361f32471'
```
### recoverPublicKey()
Recovers the signers `publicKey` from the signature.
```javascript
const signer = EthCrypto.recoverPublicKey(
'0xc04b809d8f33c46ff80c44ba58e866ff0d5..', // signature
EthCrypto.hash.keccak256('foobar') // message hash
);
// > '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.
```javascript
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.
```javascript
const message = await EthCrypto.decryptWithPrivateKey(
'0x107be946709e41b7895eea9f2dacf998a0a9124acbb786f0fd1a826101581a07', // privateKey
{
iv: '02aeac54cb45283b427bd1a5028552c1',
ephemPublicKey: '044acf39ed83c304f19f41ea66615d7a6c0068d5fc48ee181f2fb1091...',
ciphertext: '5fbbcc1a44ee19f7499dbc39cfc4ce96',
mac: '96490b293763f49a371d3a2040a2d2cb57f246ee88958009fe3c7ef2a38264a1'
} // encrypted-data
);
// 'foobar'
```
### cipher.stringify()
Transforms the object with the encrypted data into a smaller string-representation.
```javascript
const str = EthCrypto.cipher.stringify({
iv: '02aeac54cb45283b427bd1a5028552c1',
ephemPublicKey: '044acf39ed83c304f19f41ea66615d7a6c0068d5fc48ee181f2fb1091...',
ciphertext: '5fbbcc1a44ee19f7499dbc39cfc4ce96',
mac: '96490b293763f49a371d3a2040a2d2cb57f246ee88958009fe3c7ef2a38264a1'
});
// > '59ab06532fc965b0107977f43e69e5a4038db32099dab281c8f5aece2852...'
```
### cipher.parse()
Parses the string-representation back into the encrypted object.
```javascript
const str = EthCrypto.cipher.parse('59ab06532fc965b0107977f43e69e5a4038db32099dab281c8f5aece2852...');
/* > {
iv: '02aeac54cb45283b427bd1a5028552c1',
ephemPublicKey: '044acf39ed83c304f19f41ea66615d7a6c0068d5fc48ee181f2fb1091...',
ciphertext: '5fbbcc1a44ee19f7499dbc39cfc4ce96',
mac: '96490b293763f49a371d3a2040a2d2cb57f246ee88958009fe3c7ef2a38264a1'
} */
```
### signTransaction()
Signs a raw transaction with the privateKey. Returns a serialized tx which can be submitted to the node.
```javascript
const identity = EthCrypto.createIdentity();
const rawTx = {
from: identity.address,
to: '0x86Fa049857E0209aa7D9e616F7eb3b3B78ECfdb0',
value: new BN('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.
```javascript
const SolidityCli = require('solidity-cli');
// create compiled solidity-code
const compiled = await SolidityCli.compileCode(
'contract ExampleContract {...'
)[':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);
```
### calculateContractAddress()
Calculates the address for the contract from the senders address and the nonce, without deploying it to the blockchain.
```javascript
// pre-calculate address
const calculatedAddress = EthCrypto.calculateContractAddress(
account.address, // address of the sender
3 // nonce with which the contract will be deployed
);
const rawTx = {
from: account.address,
gasPrice: parseInt(gasPrice),
nonce: 3,
data: compiled.code
};
const receipt = await state.web3.eth.sendTransaction(rawTx);
console.log(receipt.contractAddress === calculatedAddress);
// > true
```
### 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. This is not a real compression, it just make your string smaller when you have to store it in utf-16 anyways.
```javascript
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...'
```