How were $6 billion stolen from Binance with genuine signatures?

In three steps, and the key never leaves the box.

1. Ask

   A customer asks to withdraw. The exchange’s normal process checks the request: risk checks, limits, the account’s balance.

2. Sign

   The request reaches a signing service that holds the hot wallet’s key. It signs. Binance’s hot wallet used MPC, a key split into shares that sign together, but the idea is the same: the service produces the signature.

3. Send

   The signed transaction goes to the blockchain, and the coins leave in minutes. That speed is why exchanges keep some money hot. Most of it sits in cold storage, offline, where moving it is slow on purpose.

A digital signature is mathematical proof that whoever controls a key approved a transaction. It says nothing about who asked. Hand the signing service a well-formed request from somewhere else and it signs that too, with exactly the same signature. A key is only as safe as whatever can ask it to sign.

Binance puts the impact at about $6.34 billion; Elliptic counts $6.43 billion and TRM Labs $6.36 billion across 10 chains. The drain ran from about 20:05 to 23:56 UTC on October 29, under four hours, and most of it left in the first half hour, by the reported times.

Three words get mixed up afterwards. Frozen: about $2.85 billion was frozen or intercepted, Elliptic says, mostly stablecoins whose issuers can block an address. Freezing stops coins moving; it doesn’t send them back, and Circle says it cannot reverse a completed USDC transfer. About $0.79 billion of the stolen stablecoins was swapped before the freezes landed. Covered: Binance says it is absorbing the loss from its own funds and had replenished about 98% of impacted assets. Recovered: that would mean stolen coins coming back, and covering is not that.

No single click, but a chain of footholds. In its November 3 findings, Binance says one engineer’s computer picked up a tampered Homebrew download in June, and another engineer was targeted with a fake job interview in September. On October 20, Binance says, an internal AI tool was used to take over other engineers’ computers. The attackers then took a container-deployment token and deployed a container that reached the internal wallet-signing service.

From there, Binance says, transactions were started through the signing service outside the normal withdrawal process, so the checks on that road never saw them. On Ethereum, the roughly 50 signed requests were EIP-7702 delegations that handed hot-wallet accounts to an attacker-controlled contract, which swept them. Binance says it found no evidence that private keys leaked.

The FBI, the Secret Service and IRS-CI attribute the theft to North Korea’s TraderTraitor group; North Korea denies it. Binance resumed withdrawals in phases from November 1.

1. 1 See

   Open Signed, Not Meant and tap Binance, Oct 29 (simplified). The attacker can reach the signer and there is no check there: Attacker’s requests reads signed, and Could leave in 4 hours reads $6.34B, the whole hot wallet.

2. 2 Change

   Tap Same attack, check at the signer. The signer now asks for a matching customer withdrawal, and the attacker’s requests have none. Attacker’s requests reads bounced, and Could leave in 4 hours $0.

3. 3 Understand

   Tap Attacker forges records too: the match passes, and only amount limits slow it, $1.00B in four hours. A person approves big ones cuts that to a trickle, $240M. Then tap Keep less money hot: with no check the loss stops at the $500M in the hot wallet, but Customer withdrawals reads hours on busy days.

Signed, Not Meant is a toy exchange with one hot wallet and three dials. The attacker’s rates, the amount limits and the four-hour stop are illustrative; only the Binance figures are sourced. Real exchanges run many hot wallets and layered controls: risk engines, rate limits, multi-party approval and monitoring.

The fix in the film, a check where the key lives that each request matches a real withdrawal, is our model of a common defence. It is not a claim about what Binance’s signer did or didn’t check; Binance has not published that. An attacker who controls both the records and the approvals beats any check that trusts them, and limits only slow a drain.

Everything on the stage is drawn in code; the request amounts and addresses are made up. The film uses 3.5 seconds of Binance co-CEO Richard Teng’s own October 30 update, credited on screen.