Signature and Verification

Basics

Ethereum white paper:

ECDSAPUBKEY(pr ∈ B32) ≡ pu ∈ B64
- Private key - 32 bytes
- Public key - 64 bytes
ECDSASIGN(e ∈ B32, pr ∈ B32) ≡ (v ∈ B1, r ∈ B32, s ∈ B32)
- signs e - 32 bytes, so a hash
- v :
  - either 'recovery id'
    - 1 byte, [27,30] but upper two invalid, so just 27 or 28
  - or {chain id × 2 + 35, chain id × 2 + 36}
Address
- Address is a 160-bit value (20 bytes)
- right most 160-bits of Keccak hash of corresponding public key

Hash

See https://github.com/ethereum/wiki/wiki/Ethash, Ethereum's hash is a varient referred to as Keccak hash

web3.sha3.then..
- two versions, to hash a string, or hash a hex representation
- the follows SHOULD (but there's an issue) get same result ("hello!" -> '0x68656c6c6f21', ascii)
  - web3.sha3("hello!");
  - web3.sha3(web3.toHex("hello!"),{encoding: 'hex'});
  - web3.sha3('0x68656c6c6f21',{encoding: 'hex'});
  - however, unreliable, see https://github.com/ethereum/web3.js/issues/1344
- NOTE: web3.sha3 does not always behave the same as in Solidity
  - tried and spent a lot time but cannot get it right
  - https://www.npmjs.com/package/solidity-sha3
    - Raine said "web3.sha3 doesn't always match the behavior of sha3 in Solidity. This one does."
    - So if truly want to build the hash in web3.js, consider this library
  - reason: non-standard packing of solidity
    - solidity keccak256(...) ... computes...of the (tightly packed) arguments
    - http://solidity.readthedocs.io/en/develop/abi-spec.html#abi-packed-mode
Solidity
- keccak56
  - may behave the same with web3.sha3 if packing is not involved
  - otherwise try a compatible library (search for it...)

  function justHash(bytes data) public pure returns (bytes32) {

    return keccak256(datea);

truffle(develop)> message = 'hello, world!'

'hello, world!'

truffle(develop)> hashMessage = web3.sha3(message);

'0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2'

truffle(develop)> vsale.justHash(message);

'0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2'

web3j (Java API)
- remote - Call server Ethereum.web3Sha3(String data).send;
  - Ethereum is an interface, use an instance of Web3j built from factory method (an Admin or connection)
  - data - must be a "0x..." hex string
  - if byte[] dataBytes, String hexData = "0x"+Hex.encodeHexString(dataBytes);
    - Hex is org.apache.commons.codec.binary.Hex;
  - hashed by geth node
  - same as from web3.js
- offline - org.web3j.crypto.Hash.sha3
  - local hash

Signature

see

https://github.com/ethereum/wiki/wiki/JavaScript-API#web3sha3
https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign
web3.js
- offline - possible but need some other libraries
- online - web3.eth.sign(address, dataToSign, [, callback])
  - address - account to sign with, needs to be unlocked
  - dataToSign - a string, any string
  - process (geth): sign(keccak256("\x19Ethereum Signed Message:\n" + len(message) + message)))
    - first adding a prefix
    - sha3 hash
    - then sign
  - result:
    - r = signature[0:64]
    - s = signature[64:128]
    - v = signature[128:130]
  - where
    - v will be either 00 or 01,
    - to use v in ecrecover, need to parse it into an integer then add 27
web3j Java API
- offline - ECDSASignature.sign
  - input: hash
  - returns something can be verified by solidity without prefix
  - however only returns R & S, what's V? (only two possibilities so guessing is practicable)
- offline - Sign.signMessage (Yes, finally find something to sign offline!)
  - input: message, DO NOT hash. will first hash then sign
  - returns V,R,S

Verification

ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address)
- recover address associated with the public key from elliptic curve signature, return zero on error

For remote (online) signature produced by a geth with prefix, consider code sample:

function buyWithKyc(uint8 v, bytes32 r, bytes32 s) public payable {

bytes32 senderAddressHash = keccak256(msg.sender);

bytes memory prefix = "\x19Ethereum Signed Message:\n32";

bytes32 prefixedHash = keccak256(prefix, senderAddressHash);

address recover = ecrecover(prefixedHash, v, r, s);

require(recover == kycSigner);

    ......

For offline signature produced by Web3j without prefix, consider code sample:

  function buyWithKyc(uint8 v, bytes32 r, bytes32 s) public payable {

      bytes32 senderAddressHash = keccak256(msg.sender);

      address recover = ecrecover(senderAddressHash, v, r, s);

      require(recover == kycSigner);

pragma solidity ^0.4.18;

contract SignVerify {

  function verifyNoPrefix(bytes32 data, uint8 v, bytes32 r, bytes32 s) public pure returns (address) {

    return ecrecover(data, v, r, s);

  function prefixHash(bytes data) public pure returns (bytes32) {

    bytes memory prefix = "\x19Ethereum Signed Message:\n32";

    bytes32 prefixedHash = keccak256(prefix, data);

    return prefixedHash;

  function justHash(bytes data) public pure returns (bytes32) {

    return keccak256(data);

  function verifyWithPrefix(bytes32 hash, uint8 v, bytes32 r, bytes32 s) public pure returns(address) {

      bytes memory prefix = "\x19Ethereum Signed Message:\n32";

      bytes32 prefixedHash = keccak256(prefix, hash);

      return ecrecover(prefixedHash, v, r, s);

NOTE: THIS IS TESTED ON A SIMULATOR (GANACHE), GETH HAS SLIGHTLY DIFFERENT BEHAVIOR

truffle(develop)> compile

truffle(develop)> migrate --reset

Using network 'develop'.

Running migration: 1_initial_migration.js

  Replacing Migrations...

  ... 0x4057db833b2401281bc978588a1648d0fd0d5dfe1b03ab9c09346387aff950f7

  Migrations: 0x8cdaf0cd259887258bc13a92c0a6da92698644c0

Saving successful migration to network...

  ... 0xd7bc86d31bee32fa3988f1c1eabce403a1b5d570340a3a9cdba53a472ee8c956

Saving artifacts...

Running migration: 2_deploy_token_sale.js

  Replacing VscToken...

  ... 0x3436474f0d575259b655f5bd1d1e89734da7c1b2dffdc72c090261407fd7c485

  VscToken: 0x345ca3e014aaf5dca488057592ee47305d9b3e10

  Replacing VscSale...

  ... 0x66d235c9af41266b1f1dd5e92fe14693939142b496246b44d0e29b9111a39a12

  VscSale: 0xf25186b5081ff5ce73482ad761db0eb0d25abfbf

Saving successful migration to network...

  ... 0x059cf1bbc372b9348ce487de910358801bbbd1c89182853439bec0afaee6c7db

Saving artifacts...

Running migration: 3_sign_verify.js

  Replacing SignVerify...

  ... 0xa4fba339ac0dc34159057acf49e18b141c5a18bbbfdceb2cea7916f39709d026

  SignVerify: 0x9fbda871d559710256a2502a2517b794b482db40

Saving successful migration to network...

  ... 0xe3e7ffb1810175cddb3670470f6c955fcb30f380ca43fd15ed823fa93047f5ce

Saving artifacts...

truffle(develop)> SignVerify.deployed().then(function(i){sv=i;});

undefined

// message and hash

truffle(develop)> message = 'hello, world!'

'hello, world!'

truffle(develop)> hashMessage = web3.sha3(message);

'0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2'

truffle(develop)> sv.justHash(message);

'0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2'

// CONCLUSION: web3.sha3 works the same as solidity keccak256

// sign

truffle(develop)> addr = '0x627306090abab3a6e1400e9345bc60c78a8bef57'

'0x627306090abab3a6e1400e9345bc60c78a8bef57'

truffle(develop)> sig = web3.eth.sign(addr, web3.sha3(message));

'0xc56b827b03d2937acb6e658be5acc2a29d93bdfb43f6bde4ac86c79bf9db8a3d2def112317d523c3cbd9cf8dd8600aba1513f862ff82f6742da21fbe5e128dff01'

truffle(develop)> r = sig.substr(0,66) ;

'0xc56b827b03d2937acb6e658be5acc2a29d93bdfb43f6bde4ac86c79bf9db8a3d'

truffle(develop)> s = "0x" + sig.substr(66,64) ;

'0x2def112317d523c3cbd9cf8dd8600aba1513f862ff82f6742da21fbe5e128dff'

truffle(develop)> v = Number.parseInt(sig.substr(130,2))+27;

// CONCLUSION: sign accepts a hex hash string

// if use JSON RPC

// bing@binginspiron:~$ curl -X POST  -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_sign","params":["0x627306090abab3a6e1400e9345bc60c78a8bef57", "0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2"],"id":1}' http://localhost:9545

// {"id":1,"jsonrpc":"2.0","result":"0xc56b827b03d2937acb6e658be5acc2a29d93bdfb43f6bde4ac86c79bf9db8a3d2def112317d523c3cbd9cf8dd8600aba1513f862ff82f6742da21fbe5e128dff01"}

// means: send a hex string (the hash)

// verify

truffle(develop)> sv.verifyWithPrefix(web3.sha3(message),v,r,s).then(function(res){console.log(res);return res===addr;});

0x627306090abab3a6e1400e9345bc60c78a8bef57

true

// CONCLUSION: remember: sign= prefix+sha3(message)=>sha3=>sign, verify = prefix+sha3(message)=>sha3, plus v,r,s => verify

// =============================== Alternative ==============================

truffle(develop)> sv.prefixHash(web3.sha3(message))

'0xbd5de6a5526167c24b6de8047a9c73c9565f7d68c1f80b28bd3467b578dc828e'

truffle(develop)> sv.verifyNoPrefix('0xbd5de6a5526167c24b6de8047a9c73c9565f7d68c1f80b28bd3467b578dc828e',v,r,s)

'0x627306090abab3a6e1400e9345bc60c78a8bef57'

// CONCLUSION: just split verifyWithPrefix into two steps, and check the intermediate result

// =============================== Alternative ==============================

// THIS IS TESTED ON Ropsten, SIGNATURE's V is 1B which is 27

bing@binginspiron:~/git/vsc/ethereum$ truffle console --network testnet

truffle(testnet)> message = 'hello, world!'

'hello, world!'

truffle(testnet)> hashMessage = web3.sha3(message);

'0xfbc3a5b569f80319726d3cc77c708b0d34633e5672aac0699ea6ffa500d0bee2'

truffle(testnet)> addr = "0x30514f8346771d10d8c74f873abfc4050fb17acb"

'0x30514f8346771d10d8c74f873abfc4050fb17acb'

truffle(testnet)> sig = web3.eth.sign(addr, web3.sha3(message));

'0x546c5148760c3f07039ca1b79105fa4fd64dcd56d196e37df2cc9c70efc235ff4e2fd15d5f9982327afe5e91ab9fd5a2245f086b0270a4b92b4e289cba4694521b'

truffle(testnet)> migrate --reset

Using network 'testnet'.

Running migration: 1_initial_migration.js

  Deploying Migrations...

  ... 0xd87a4f46718a66c4a91a13ccfc8c222997f37265d0650fb7567f440165f4e79e

  Migrations: 0x906b5a7de3a8578383ec9b64338764d645320017

Saving successful migration to network...

  ... 0x4be5f3ef032d65d7f06cf1e8075c5c50ae2b185cb9116703f1089b2fa5b11a67

Saving artifacts...

Running migration: 2_deploy_token_sale.js

  Deploying VscToken...

  ... 0x6107c51252401527d86d09e30925fc1d1e56e457da6ea768ce351cda5cbef922

  VscToken: 0xf6dceeee960fd6e15abcbba21ccf971eb0f98e87

  Deploying VscSale...

  ... 0xb833a1d22dd2e340e58a879a9997c4e81cdf2e26ff1e6662fa714ec32d337872

  VscSale: 0x95dd5c6d0ea6a20997fe0812d6a2cb268dcf9a9b

Saving successful migration to network...

  ... 0xa5658bc3e44bfb79c7130c0aac82df155ffa406eaaae6d3a9f4ca92e1f4d92b9

Saving artifacts...

Running migration: 3_sign_verify.js

  Deploying SignVerify...

  ... 0xfb8dd0bd8bd7acfb0746c93c3c1600e0a2c523ddd50cb7d424d732b52075c3dc

  SignVerify: 0x903ac8154848b642dfd16f20999bfb0e1630ebf9

Saving successful migration to network...

  ... 0xfef20f3d56311e9682ddd369740326d86deace8bd4998c0f660831230f14d34e

Saving artifacts...

truffle(testnet)> SignVerify.deployed().then(function(i){sv=i;});

undefined

truffle(testnet)> r = sig.substr(0,66) ;

'0x546c5148760c3f07039ca1b79105fa4fd64dcd56d196e37df2cc9c70efc235ff'

truffle(testnet)> s = "0x" + sig.substr(66,64) ;

'0x4e2fd15d5f9982327afe5e91ab9fd5a2245f086b0270a4b92b4e289cba469452'

truffle(testnet)> sig.substr(130,2);

'1b'

truffle(testnet)> sig

'0x546c5148760c3f07039ca1b79105fa4fd64dcd56d196e37df2cc9c70efc235ff4e2fd15d5f9982327afe5e91ab9fd5a2245f086b0270a4b92b4e289cba4694521b'

truffle(testnet)> v = Number.parseInt(sig.substr(130,2),16);

truffle(testnet)>  sv.verifyWithPrefix(web3.sha3(message),v,r,s).then(function(res){console.log(res);return res===addr;});

0x30514f8346771d10d8c74f873abfc4050fb17acb

true

truffle(testnet)>

A function may need for converting hex string to string

function hexToString (hex) { var string = ''; for (var i = 0; i < hex.length; i += 2) {string += String.fromCharCode(parseInt(hex.substr(i, 2), 16));}return string;}

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