3 ms·
I didn't know we can brute-force SHA256 in a lifetime, yet. Is it already possible?...
by cvs268 10y ago
I didn't know we can brute-force SHA256 in a lifetime, yet.
Is it already possible?...
- ikeboy 10y agoYou can easily bruteforce against a dictionary. They're getting 6 million passwords/sec checked. Not enough to get an arbitrary hash, though.
- iancarroll 10y agoEssentially, your backups are encrypted with a key that is generated using a key derivation function (KDF), which takes in your password and outputs a "hash" that is fed into the encryption algorithm. It's obviously much faster to brute force SHA256(dictionary_word) than a 128-bit key. Apple was previously using 10,000 rounds of SHA-1 (with PBKDF1) as a KDF. This is much slower than one round of SHA-2 they've switched to by orders of magnitude.
- Quiark 10y agoIf you only try the passwords that people are likely to use then... Yes
- brazzledazzle 10y agoWould using a bunch of previous password leaks to create a rainbow table be useful for programs that do this? With the number of leaks it seems like it would be a pretty accurate depiction of how a lot of people choose passwords.
- iancarroll 10y agoYes. However, rainbow tables are trivially mitigated with a random salt, which requires you to regenerate your table for every hash. I don't know if iTunes uses a salt to encrypt the backup.
- mrb 10y agoANY standard hash function (SHA256, SHA512, even SHA3) used to obfuscate a password can easily be brute forced if the password has low entropy (like BigBlue8 or s3cr3tp4ssw0rd). These passwords are weak and hash functions are designed to be fast to compute, so it's possible to brute force them. To brute force successfully SHA256, you don't necessarily need to brute force 2^256 possibilities, you need to brute force a much smaller list of likely passwords, and this might just be enough.