I have a method in solidity and wants to return the sent string only for the owner address.

function greet(string str) returns(string) {
    if (msg.sender == owner) {
    return str;
    } else {
        return "Sorry I respond only to my owner";

In Rinkeby testnet, I am able to set the address directly without unlock or signing with private key web3.eth.defaultAccount = '0xC2107dFbCf6a70865f30fc439b1850bE434231c9';

and when i greet.call('Hello').... method I get the passed string returned perfectly and gets back 'Hello'

So my question is can anyone use my public address in web3.eth.defaultAccount and call the greet method ? I want only owner with private key can pass the test (msg.sender == owner). How can others without private key get through it ?

1 Answer 1


In rinkeby this is only possible if:

  • The account has previously been unlocked when starting geth with the - - unlock version

  • The account has previously been unlocked from the geth command line by typing personal.unlockAccount(...)

  • The method is of type pure, view or constant (being this latter one deprecated)

so to answer shortly, only those with the private key can actually do it.

  • The account was not unlocked in geth command. I created this account from myetherwallet. In my node.js code, I use web3 and connect directly to new Web3.providers.HttpProvider('rinkeby.infura.io/') For the first time I had only created a contract with this account by sending a rawsignedtransaction in the beginning by signing it with my privatekey.
    – antjohns
    Dec 14, 2017 at 22:41
  • 1
    I believe your usage falls into the third bullet point. You're calling a view function, which means you do not need to send a transaction and thus don't need a private key (since there's nothing to sign).
    – user19510
    Dec 14, 2017 at 23:10

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