What is ERC-20

1. contract TokenContractFragment {

2.  // Balances for each account  
   

3.  mapping(address => uint256) balances;
   

4.  // Owner of account approves the transfer of an amount to another account  
   

5.  mapping(address => mapping (address => uint256)) allowed;
   

6.  // Get the token balance for account \`tokenOwner\`  
   

7.  function balanceOf(address tokenOwner) public constant returns (uint balance) {  
   

8.      return balances\[tokenOwner\];  
   

9.  }
   

10.  // Transfer the balance from owner's account to another account  
    

11.  function transfer(address to, uint tokens) public returns (bool success) {  
    

12.      balances\[msg.sender\] = balances\[msg.sender\].sub(tokens);  
    

13.      balances\[to\] = balances\[to\].add(tokens);  
    

14.      Transfer(msg.sender, to, tokens);  
    

15.      return true;  
    

16.  }
    

17.  // Send \`tokens\` amount of tokens from address \`from\` to address \`to\`  
    

18.  // The transferFrom method is used for a withdraw workflow, allowing contracts to send  
    

19.  // tokens on your behalf, for example to "deposit" to a contract address and/or to charge  
    

20.  // fees in sub-currencies; the command should fail unless the \_from account has  
    

21.  // deliberately authorized the sender of the message via some mechanism; we propose  
    

22.  // these standardized APIs for approval:  
    

23.  function transferFrom(address from, address to, uint tokens) public returns (bool success) {  
    

24.      balances\[from\] = balances\[from\].sub(tokens);  
    

25.      allowed\[from\]\[msg.sender\] = allowed\[from\]\[msg.sender\].sub(tokens);  
    

26.      balances\[to\] = balances\[to\].add(tokens);  
    

27.      Transfer(from, to, tokens);  
    

28.      return true;  
    

29.  }
    

30.  // Allow \`spender\` to withdraw from your account, multiple times, up to the \`tokens\` amount.  
    

31.  // If this function is called again it overwrites the current allowance with \_value.  
    

32.  function approve(address spender, uint tokens) public returns (bool success) {  
    

33.      allowed\[msg.sender\]\[spender\] = tokens;  
    

34.      Approval(msg.sender, spender, tokens);  
    

35.      return true;  
    

36.  }  
    

37. }

ERC-20 is available on Github.

References:

https://theethereum.wiki/w/index.php/ERC20_Token_Standard

Is ERC-20 approve dangerous? Allowances, permit and infinite approvals

Approve is safe; unlimited, forgotten allowances and unread permit signatures are not. Approve exact amounts, use permit with short deadlines, read every typed-data signature, and revoke old approvals.

#security#tokens#wallets