Key Compromise
One of the more common attacks in the traditional info-sec world is to compromise private keys which are responsible for safeguarding data or value. In interoperability protocols, key compromise strikes at the root-of-trust, and allows attackers to compromise the verification mechanism itself.
In the interoperability category, the best example is the Ronin Network Bridge Exploit, which led to over $600M being stolen once 5-of-9 validator keys were breached.
How They Work
Key compromise attacks are the most brute force way of compromising trust-network based systems. In externally verified systems like multisigs, validator systems and oracle networks, a majority of keys being breached is sufficient to execute an attack on the system. In the common security adage — defense always has to be right, whereas offense only has to be right once.
There are two primary vectors that attackers probe to compromise keys — infrastructure vulnerabilities and social engineering.
Infrastructure Vulnerabilities
Private keys in interoperability systems often are "hot" keys, which means that they are exposed to a public network (aka the internet) in order to be able to receive requests and sign messages without human intervention. Contrast this to "cold" keys which are often stored on a hardware device like a Ledger and require manual intervention to sign messages.
Naturally, hot key setups allows for greater speed and liveness guarantees in the context of bridging. However, the trade-off is that they need to expose an interface to the internet at all times.
This is precisely what attackers target in infrastructure attacks — they probe external verifiers' setups looking for a hole by which they can access and decrypt keyfiles, and sign messages without the honest verifiers' knowledge.
Social Engineering
Often, phishing and other social engineering techniques are used to gain access to confidential information, which is then used to attack or compromise the system. While not as technically sophisticated as infrastructure attacks, social engineering maneuvers are often much cheaper and far more effective, as humans are more malleable and dynamic than computer systems.
Methods leveraged by attackers include:
Posing as a coworker or friend and asking for sensitive information
Exposing links that look authentic but lead to malware or spyware being installed
Infiltrating organizations, building rapport, and accessing confidential information through clearance
These may seem farfetched, but per the Ronin Network attack described above, these attacks do happen and the ROI is extremely high for attackers. Once attackers socially engineer their way into accessing keys, the end result is the same as infra attacks — the system gets rugged.
Defense
Nomad's Revocation-Centric Design
Nomad's design is inherently defensive against key compromise by splitting responsibility across two classes of actors:
Updaters — have the permissions to verify cross-chain messages
Watchers — have the permissions to revoke, or disconnect, applications from Replicas
For example, let's examine a setup where Nomad has one Updater and 8 Watchers. A common question we get is, "isn't this functionally equivalent to a 9-of-9 multisig address?"
The answer is no. In the multisig setup, if all 9 keys are compromised, cross-chain messages can be corrupted. In Nomad, even if all 9 keys are compromised, as long as any one Watcher operator has a redundant setup with a copy of the key, they can still sign messages to flag fraud and protect the system.
Operational Security
In addition to being designed to resist key compromise, the Nomad core team also follows security best practices to reduce the chances of any infrastructure or core team members being compromised.
From an infrastructure standpoint, we:
Have an internal SRE team following best practices in key management
Conduct regular internal audits on our systems
Provision strict access to sensitive key material
Run redundant setups of critical agents
Are progressively decentralizing the system to include more agent operators
From a social standpoint, we:
Remain vigilant and have internal guidance around social attacks
Only give access to sensitive information on a need-to-know basis
Conduct fake attacks to ensure team members are responding appropriately
For obvious reasons, we are only sparingly sharing details right now, while we determine what is acceptable to share. We will continue to add more details in the Audits section.
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