5 ms·

If this were true, there would be no reason to hash passwords. There are hashing algorithms (bcrypt, scrypt, PBKDF2) that are specifically designed to be slow

by sdevlin 14y ago

If this were true, there would be no reason to hash passwords. There are hashing algorithms (bcrypt, scrypt, PBKDF2) that are specifically designed to be slow to prevent these attacks.

Joeri 14y ago
PBKDF2 is not memory hard, so even with known technology it can be broken relatively easy. Bcrypt seems secure for now, but you shouldn't rely on security through obscurity, which is essentially what putting faith in the irreversability of a hash is. The reality is that if a hashed password leaks, you should assume it will be broken. It's like with bank vaults. They're not designed to withstand attack, just to delay it. Well-hashed passwords delay attack, but they do not prevent it.
- benaiah 14y ago
  Hashes are mathematically proven to be irreversible except through rainbow tables (easily beaten with salting) or brute force. There's no faith needed (well, I suppose that non-mathematicians like myself have to put faith in the math, but I trust the hundreds of independent studies of these algorithms quite well), and it's not anything close to "security through obscurity". That said, you are right. You should always change passwords that are leaked. This, however, is due to the poor security practices of most companies, not some bizarre distrust of hashes.
  - Joeri 14y ago
    Brute force was exactly what i was talking about. It doesn't matter whether a hash is broken through a mathematical flaw, or through improvements in the brute forcing process, if in practice it still gets broken. Once a hash is leaked brute force becomes possible in theory, and what is possible in theory is usually possible in practice with sufficient dedication. There have been such huge improvements in hashing through tools like hashcat and hardware implementations that i don't think it's unreasonable to distrust hashes. Once a hash is leaked you're essentially hoping that brute forcing it is too high of a cost. Given the history of order of agnitude improvements in hashing speed, i consider it unreasonable to believe that any password database remains safe indefinitely once leaked. I find your trust in the difficulty of brute forcing a hash just as bizarre as you seem to find my distrust of hashes.

by sdevlin 14y ago

If this were true, there would be no reason to hash passwords. There are hashing algorithms (bcrypt, scrypt, PBKDF2) that are specifically designed to be slow to prevent these attacks.

Joeri 14y ago

PBKDF2 is not memory hard, so even with known technology it can be broken relatively easy. Bcrypt seems secure for now, but you shouldn't rely on security through obscurity, which is essentially what putting faith in the irreversability of a hash is. The reality is that if a hashed password leaks, you should assume it will be broken. It's like with bank vaults. They're not designed to withstand attack, just to delay it. Well-hashed passwords delay attack, but they do not prevent it.

benaiah 14y ago
Hashes are mathematically proven to be irreversible except through rainbow tables (easily beaten with salting) or brute force. There's no faith needed (well, I suppose that non-mathematicians like myself have to put faith in the math, but I trust the hundreds of independent studies of these algorithms quite well), and it's not anything close to "security through obscurity". That said, you are right. You should always change passwords that are leaked. This, however, is due to the poor security practices of most companies, not some bizarre distrust of hashes.
- Joeri 14y ago
  Brute force was exactly what i was talking about. It doesn't matter whether a hash is broken through a mathematical flaw, or through improvements in the brute forcing process, if in practice it still gets broken. Once a hash is leaked brute force becomes possible in theory, and what is possible in theory is usually possible in practice with sufficient dedication. There have been such huge improvements in hashing through tools like hashcat and hardware implementations that i don't think it's unreasonable to distrust hashes. Once a hash is leaked you're essentially hoping that brute forcing it is too high of a cost. Given the history of order of agnitude improvements in hashing speed, i consider it unreasonable to believe that any password database remains safe indefinitely once leaked. I find your trust in the difficulty of brute forcing a hash just as bizarre as you seem to find my distrust of hashes.