How to store Public Key in Ethereum contract?

Question

I want to store a Public Key of an Ethereum address in a contract. What is the advisable primitive datatype to store a Public Key?

1. Should I store as String or Bytes32?
2. Is it secure to store a Public Key in a contract? I know it is PUBLIC key, but still...I want to know any pitfalls that I should be mindful of.

Thanks!

Answer 1

Always store keys as bytes since strings in some languages are known to be terminated by null value bytes. You can use a bytes32 attribute to store the key and a getter method to retrieve it from the deployed (instantiated) contract:

contract PubKey {
         bytes32 pubKey;

         function PubKey(bytes32 initKey) {
             pubKey = initKey;
         }

         function getPubKey() constant returns (bytes32) {

            return pubKey;

         }
    }

Edit:

The public key is 64 bytes long excluding its prefix:

contract PubKey {
    uint8[] pubKeyBytes;

    function PubKey(uint8[] initKey) {
       for(uint i = 0; i < initKey.length; i++) {
          pubKeyBytes.push(initKey[i]);
       }
}

function getPubKeyByte(uint i) constant returns (uint) {
    return pubKeyBytes[i];
}

This is expensive since each retrieval of the public key must be called 64 times. using two 32 byte chunks is cheaper (but uglier):

contract PubKey {
     bytes32 pubKeyHalf1, pubKeyHalf2;

     function PubKey(bytes32 initKeyHalf1, bytes32 initKeyHalf2) {
         pubKeyHalf1 = initKeyHalf1;
         pubKeyHalf2 = initKeyHalf2;
     }

     function getPubKeyHalf1() constant returns (bytes32) {
        return pubKeyHalf1;
     }

     function getPubKeyHalf2() constant returns (bytes32) {
        return pubKeyHalf2;
     }
}

Answer 2

You can also store the public key in bytes variable, but that will consume more gas. In my simple test, storing a public key in two bytes32 variables uses ~ 67,000 gas, and storing it in one bytes variable uses ~85,000 gas