I have memorized a very long and secure passphrase, that when hashed with sha256, I can use the result as an ECDSA private key, and use it as a brain-address for Bitcoin.
Now I need more bitcoin addresses, and instead of memorizing a new long and secure passphrase, I am thinking about just hashing the previous hash, over and over again to create new keys.
So I can build a simple software to which I type the passphrase and I tell him I want the key of the address number 58, so it just has to sha256 the passphrase 58 times to get that key.
If the greatest hacker ever had for example the first 500 bitcoin addresses that were generated with my passphrase, and if that hacker knew how those private keys where generated, would he have any chance to hack this system?
I am pretty sure he wouldn't but I want to make sure, because this is for a project at my job.