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Major security hole in Hyperledger Fabric - Private Data

evantsang Posts: 1
edited October 2019 in LFS272 Class Forum

Private data is marketed as a data security solution in Hyperledger Fabric. Unfortunately, this is just another serious security whole somehow went under the radar, and all projects using this function are in risk.

It amazes me that nobody had mentioned this before so I guess I better point this out now before more damages are being done.

The logic behind Private Data is simple, it put data in a local embedded data store and put a hash of that data on blockchain.

The issue is that cryptographic hash is not an encryption mechanism, same data hashed by anyone using the same hashing algorithm (which is also very standardized) will always get the same hash! This is exactly what hash functions are designed for, and that’s why we use hash in digital signature to allow anyone to validate signed data. However, this also means anyone can “decrypt” the data behind the hash by using dictionary attack.

Hashing is cheap, the cost of each hash on a normal laptop cpu core is about 3 microseconds, basically I can create 1 billion candidate hashes within one hour on a single laptop cpu core, and compare them to the hashes on hyperledger fabric DLT. And I am just talking about using a single core on my laptop, not even 50% power of my laptop

Why is it dangerous? Because if an attacker is connected to a blockchain system, the attacker know the range of the data being hashed (etc, trade ID, item name, bank name, address, cell phone number), so you can easily create dictionary attack to get the true data behind the hash out.

How about adding salt to each data to be hashed? Well, that’s one thing Hyperledger Fabric didn’t do. To their defense, hyperledger didn’t implement salt because it is difficult to pass salts to counter parties. You can’t use DLT to pass salt value because attackers would see it, so you have to create another p2p connection with counter party.

If you need to create connection with all the counter parties, what’s the point of using blockchain in the first place? It’s just scary that so many people are using this security whole. Sure, the hashed data maybe so big that it is unreasonable to perform dictionary attack , you better be very careful before you use this private database and make sure other peers of the network can't launch dictionary attack against you



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