Blind signing, and verifying the payload

Graduate · enrolled learners

This lesson opens with Bybit, 21 February 2025.

What happened

Bybit is a large cryptocurrency exchange. On 21 February 2025 about 1.4 billion dollars was taken from a cold wallet, the largest theft in the industry's history. The wallet was a Gnosis Safe multisig, and its signers used hardware wallets. The attacker, attributed to North Korea's Lazarus group, had injected malicious JavaScript into the Safe{Wallet} interface through a compromised Safe developer machine, so that the signers saw what looked like a routine transfer, while the transaction they actually authorized executed a delegatecall that replaced the Safe's logic with an attacker-controlled contract, handing over the wallet. Crucially, the signers were blind signing: many hardware wallets do not decode a Safe multisig transaction into a human-readable action, and Bybit's CEO said he did not verify the transaction data on his Ledger before signing. They approved data they did not read, and the data did not do what the screen claimed.

The decision point

The last lesson's fix, verify the payload on the device, assumes the device shows a payload a human can verify. Bybit is the case where it did not: the signers were blind signing, approving data their devices did not decode into a readable action, and undecoded data, which on a device that cannot parse it is shown as a raw hash, tells a signer nothing about what the transaction does. Blind signing is authorizing an effect you cannot read, and it converts a hardware wallet from a verification tool into a rubber stamp, because the one thing the signer could check, does this match my intent, is exactly what an opaque hash denies them. The discipline is to refuse it: to sign only what can be decoded into a human-readable action and checked against a written intent, and to treat a transaction that can only be blind-signed as one that cannot be safely signed at all. A billion-dollar wallet approved on a hash is a billion dollars approved on trust in a screen.

Recorded loss

$1,400,000,000

Orientation and Year One are open: anyone can read them without an account. From Year Two onward the lessons are for enrolled learners, because progress through the later years only means anything if it is tracked against a record.

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