 Είμαι η Γιάννης και είμαι ένας κομμάτις κομμάτις. Έγινε για τέτοια δεύτερη ευκαιρία και για τα πράγματα που χρειαζόμαστε με τέτοια δεύτερη ευκαιρία, έχουμε τέτοια δεύτερη ευκαιρία από τα πιο ευκαιρία που έχουμε. Και κάποιες φορές βίνουμε πολύ ενδιαφέρονες δεύτερες σχέδια, όπως το ένα που θα συγκρίνω σήμερα. Είναι αυτό το δεύτερο εύκολο που βρήκαμε από ένα κόλλεδο μου, ο name Kenan. Γιατί θα πρέπει να κομμάσουμε για αυτό το ατάξυμα, γιατί αυτό το ατάξυμα είναι πολύ σημαντικό. Είναι αρκετά έναν ατάξυμα νοβολογικό. Δεν many people know about this, και είναι often neglected by both auditors and developers. Αυτό το ατάξυμα είναι βέβαια από την ευκαιρία μετά με δύο δεύτερες πρότοκολες. Και αυτές τις ευκαιρήσεις βλέπουν πολύ πιο ευκαιρία, γιατί έχουμε ένα σπίτι πολύ νέο και πολύ!!!!!! Γιατί know we built based on these defile blocks. What makes this attack more interesting is that it actually affected protocols that integrate with Carer Finance. One of the most famous exchanges out there. As a matter of fact, the total funds that were at risk were more than 100 million. So we're talking about a lot of money here. So, first of all, what is re-entrances? Πρώτα από όλοι, τι είναι η ριέντραση. Η ριέντραση παίρνει μια εξεκουσία για το σημαρκόντρατο, και το σημαρκόντρατο δεν έχει been fully updated, και το κοντρολό είναι παίρνει σε έναν άλλο σημαρκόντρατο, που μπορεί να χρησιμοποιηθεί, μια εξεκουσία για το σημαρκόντρατο, που το σημαρκόντρατο δεν έχει been finalized. Από τώρα, η τραδιστική ριέντραση was concerned only with entry points that modified the state, but as we will show, this is not the case here. So, just to give you the textbook example of a re-entrancy, we have this re-entrant contract, and users can deposit and withdraw ether from it, and actually when a user tries to withdraw, then when the native ether is sent to the receiver, the receiver has the opportunity to run arbitrary code, and what a receiver, a malicious receiver can do, can call this withdrawal function again, and since the state has not been fully updated, and his balance is not set to zero, they can successfully call withdrawal all again, and essentially get more ether than what they had deposited. So, this can be easily fixed, and people deal with this problem by reducing this non-rental modifier. So, if we visit the same function again, we cannot call withdrawal all again when we receive ether, because the lock is true, and the whole transaction will fail. However, nothing prevents the malicious user from making a call to another contract which reads the state of this contract. So, if someone reads the state at this point, what they're going to see is that the total supply has been reduced, but the balance of the user has not been set to zero. This means that the ratio, for example, is not going to be correct. So, this is a different attack from the known re-entrant sim. So, let's get to Kerb, and what happened there. As you know, Kerb is a decentralized exchange. There are many pools in Kerb. The pool that was affected by this attack was a pool that contains native ether and staked ether. As you might know, users are liquidity providers, they can add liquidity to a pool, and of course, they can remove liquidity. So, what happens when users remove liquidity? Well, first, the LP tokens they hold is burned. So, we can think that the total supply of the LP token is reduced. And then, one by one, the tokens are sent to the user. And the first token that is sent is native ether. So, upon the receivable of this native ether, a user, a malicious user, has the opportunity to make an arbitrary call. Of course, they cannot call Kerb because it's protected by a non-re-entrant modifier. However, what they can do is they can make a call to another protocol that reads the state of this pool. And how protocols usually read the state is by using this getVirtualPrice function that they have down below. So, let's inspect this a little bit. So, the getVirtualPrice depends on this defactor, which depends on the balances. Remember, we have only updated the balance of the ether, but not the balance of the state ether, and also depends on the token supply. And remember, we reduced the token supply. So, what we achieved here is we essentially pumped this getVirtualPrice. So, this function is used to give an approximation of the value of the LP token. So, imagine that we have a protocol that holds these LP tokens. During this attack, the price of the LP token is pumped, and then the protocol will think that it holds more money than it should. Read only re-entrance is still a re-entrance in the sense that the storage update is not fully finalized, but the big difference is that we read the state. We don't try to access a function that modifies the state of the function. So, how can we prevent this attack? So, one way is to make this log that I showed you before in the non-re-entrant modifier to make it public. This works for new protocols that are being developed, but what can we do for old protocols? Well, the solution that we've seen to be more efficient is when you try to read the state of a smart contract, first try to call a function that is non-re-entrant protected. If this call fails, then it means that you are in the middle of re-entrancy, and you shouldn't read the state of the contract. So, that's it for me. Actually, we just published this attack. Feel free to read more about it. Thank you very much.