Resources

People often ask me "How did you learn how to hack?" The answer: by reading. This page is a collection of the blog posts and other articles that I have accumulated over the years of my journey. Enjoy!

SecondFi is a wallet primarily for the Cardano platform. Recently, multiple users had their wallet drained. This is the story of what happened.

The signature type for the Cardano is extended Ed25519. The wallet stores a 64-byte extended secret key that is split into a signing scalar, and a secret nonce prefix. The nonce is derived by hashing the nonce with the transaction body together.

The nonce on these signatures must remain secret. Otherwise, some basic math can be used to recover the key. Instead of using the secret nonce prefix, and transaction body alongside a hash as the secret, the nonce was computed r = SHA512(M). Notably, the blockchain has no way to determine that the nonce was insecurely generated or not. For details on how to recover the key, read this part of the article.

Any user that signed a transaction from June 8th-June 23rd, 2026 used the new vulnerable implementation. This led to over 300 wallets getting drained because their private key had been discovered. There's a good breakdown of the bug here as well. All in all, $2.4M was stolen.

How did this get into production? The wallet originally used cardano-serialization-lib under the hood. In a rewrite to the SDK to do it in-house, the per-user secret nonce was not included in the hash, leading to the bug. They were planning on doing an audit post release but this doesn't help very much.