Case Very easy case, you have 100 DAI/USDC/USDT. You wanna transfer some to your friend but you have no ETH in your wallet :( Okay, let's find the solution starting with DAI Simple Way Of course, you can “just transfer some dust ETH to the account” BUT: So let’s find another way // Another way Let's dive into the code https://etherscan.io/toke /0x6b175474e89094c44da98b954eedeac495271d0f#code Scrolling it down… aand see that picture: // --- Approve by signature ---
function permit(address holder, address spender, uint256 nonce, uint256 expiry,
               bool allowed, uint8 v, bytes32 r, bytes32 s) external
{
   bytes32 digest =
       keccak256(abi.encodePacked(
           "\x19\x01",
           DOMAIN_SEPARATOR,
           keccak256(abi.encode(PERMIT_TYPEHASH,
                                 holder,
                                 spender,
                                 nonce,
                                 expiry,
                                 allowed))
   ));

   require(holder != address(0), "Dai/invalid-address-0");
   require(holder == ecrecover(digest, v, r, s), "Dai/invalid-permit");
   require(expiry == 0 || now <= expiry, "Dai/permit-expired");
   require(nonce == nonces[holder]++, "Dai/invalid-nonce");
   uint wad = allowed ? uint(-1) : 0;
   allowance[holder][spender] = wad;
   emit Approval(holder, spender, wad);
} There is a permit function(see reference ). https://eips.ethereum.org/EIPS/eip-2612 Function designed to be callable from any account, so if you want to give allowance for transfer, you don’t need to make a transaction anymore. Rather, you can generate a permit signature off-chain and send it to your friend by any messanger, even WhatsApp :) Deeper explanation Arguments: holder - address who gives allowance spender - address who can spend allowance nonce - sequence number of permit (used to avoid ) replay attack expiry - deadline timestamp, if you didn’t use permit till that timestamp it will be invalidated allowed - boolean flag, if true you make infinite allowance, if false - revoke allowance v, r, s - ethereum signature, more details How that works: The key idea is elementary, the user makes the signature of “allowance” using own private key, then the contract can verify that using built-in ecrecover function. “Allowance” is just the set of parameters of permit (like holder, spender, etc.) and service constants (see EIP for details). Algorithm: User chooses parameters User calculates keccak256 hash of paraments + service info User signs hash from the previous step User sends signature and parameters to friend off-chain Friend sent a transaction with the permit and transfer tokens from the users’ account What about USDC/USDT ? USDC Here is the source code, basically, there is similar mechanics with the permit. But for one-time transfers is better to use function. contract transferWithAuthorization USDT Here is the souce code contract USDT doesn’t have permit mechanics and it’s cannot be implemented since the contract is non-upgradable.

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