Curriculum·G401 Custody Operations and Key Ceremonies·about 31 min
Multisig governance for an institution
By the end of this lesson you can
- →Explain that a multisig's security is its threshold and the independence of its signers, not the number of keys
- →Explain how a 2-of-5 threshold let attackers drain about 100 million dollars from the Harmony bridge
- →Compute why the effective security of a multisig is the smallest set of signers an attacker must compromise
- →Design a multisig's threshold, signer independence, and lifecycle for an institution
Graduate · enrolled learners
This lesson opens with Harmony Horizon bridge, June 2022.
- What happened
- The Harmony Horizon bridge, which moved assets between Ethereum and the Harmony chain, was controlled by a multisig that required only 2 of 5 signatures to authorize a transfer. In June 2022 attackers, later attributed to the North Korea-aligned Lazarus group, compromised two of the five signer keys, which was all the threshold demanded, and used them to drain about 100 million dollars. Five keys existed, and the security of the whole bridge was the security of any two of them, because two signatures moved everything. The keys were not independent enough and the threshold was not high enough for the value at stake: an attacker did not need to beat five, they needed to beat two, and against a determined state-linked group, two was reachable. The number of keys looked reassuring and the threshold is what actually decided the system's strength.
- The decision point
- A multisig's headline, five keys, hides the number that matters, the threshold, and an institution that reads the wrong one builds Harmony. The security of a multisig is not how many keys exist but the smallest set of signers an attacker must compromise to reach the threshold, which for a 2-of-5 is two. So multisig governance is three deliberate choices. The threshold, set high enough that compromising the required number is genuinely hard for the value and the threat, which for a hundred-million-dollar bridge against a state actor is not two. The independence of the signers, so that the required signatures sit with different people, organizations, devices and locations, and no single compromise, phishing campaign, or insider can gather several at once. And the lifecycle, so a signer who leaves, is compromised, or loses a key can be removed and replaced without freezing the assets or lowering the bar. Harmony is a multisig that got the count right and the governance wrong.
- Recorded loss
- $100,000,000
What you will be able to answer
- →Why did Harmony's multisig fail?
- →What determines a multisig's security?
- →What are the three choices of multisig governance?
- →Why does signer independence matter?
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.
It is free. We do not sell the list and there is nothing to buy at the end of it.
Sources and review
- https://rekt.news/harmony-rekt
- https://www.halborn.com/blog/post/explained-the-harmony-horizon-bridge-hack
- https://www.elliptic.co/insights/over-1-billion-stolen-from-bridges-so-far-in-2022-as-harmony-s-horizon-bridge-becomes-latest-victim-in-100-million-hack/
- https://www.fbi.gov/news/press-releases/fbi-confirms-lazarus-group-cyber-actors-responsible-for-harmonys-horizon-bridge-currency-theft
Confidence high·Volatility low·Reviewed 2026-09-16·Owner unassigned
Contested
Harmony estimated the loss at about 100 million dollars when it reported the theft on June 24, 2022, and Elliptic put it at 99.7 million. The 2-of-5 threshold and the two compromised signer addresses are in rekt and Halborn. On January 23, 2023 the FBI said it had confirmed that the Lazarus Group (APT38), cyber actors associated with North Korea, was responsible, and that the intrusion used the TraderTraitor malware campaign.
How the two keys were taken is not fully public. Halborn reports that they were protected by a passphrase and a key management service and that the attacker managed to access and decrypt multiple keys; rekt, writing the day of the theft, said the vector remained unknown.
This lesson uses Harmony for the threshold-and-independence point; the exact custody setup of the signer keys is described across analyses and some operational details remain private.