5 ms·

Curious, if the attacker knows what the encryption algorithm is, does it help them at all in breaking it? I.e., does it potentially delay breaking it by not rev

by NoPiece 14y ago

Curious, if the attacker knows what the encryption algorithm is, does it help them at all in breaking it? I.e., does it potentially delay breaking it by not revealing it?

UnoriginalGuy 14y ago
In theory, yes, in practice it is fairly obvious how something is hashed just by eye. Different hash algorithms produce different output (lengths, starting character, and spread). So with some experience you can often tell (or guess and test) what something is hashed with.
- tobyjsullivan 14y ago
  I would say that's not really true. The output hash will look the same if I apply a simple salted SHA-1 with a salt or if I apply 500 MD5's followed up followed up with 200 SHA-1's, each salted differently. I'm not a security expert, but I think this is closer to best practice these days. That said, revealing the exact algorithm would basically be throwing people with weak passwords to the wolves while really only supplying the rest of us with a false sense of security (because it will probably be cracked anyway). We'd also be better off if they didn't announce the algorithm if the passwords get leaked (like with LinkedIn).
  - gcr 14y ago
    For practice, see if you can't identify the hashing algorithm for the following stored passwords: $6$AhHvI8ay$I0ED2wWVU9eheJKvCxzcbc/ZYRoN60q5XNHruYp8yFlQvEOjJ1WtIHUwjG6L4ZGntf3ei8osB7s2GYdkN01gx1 dGhpcyBpcyBzdHVwaWQKCg== 286755fad04869ca523320acce0dc6a4 some_salt:ac01346ad1553221506dd091800a1974 c8fed00eb2e87f1cee8e90ebbe870c190ac3848c 6b3a55e0261b0304143f805a24924d0c1c44524821305f31d9277843b8a10f4e /5L0cR/wpFqSA Note how they don't look the same, so it's quite easy for an attacker to tell the difference. Want to see how you did? Here's the answer key, in base64: MTogTW9kZXJuIGNyeXB0LCBsaWtlIHRoZSBraW5kIHlvdSdkIGZpbmQgaW4gL2V0Yy9zaGFkb3cK MjogSnVzdCBiYXNlNjRpbmcgdGhlIHJhdyBwYXNzd29yZCAoc3R1cGlkKQozOiBVbnNhbHRlZCBt ZDVzdW0KNDogbWQ1c3VtLCB3aXRoIHNhbHQgcHJlcGVuZGVkCjU6IFVuc2FsdGVkIHNoYTFzdW0K NjogVW5zYWx0ZWQgc2hhMjU2c3VtCjc6IE9sZCBVTklYIGNyeXB0KCk=
- reyan 14y ago
  The definition of a symmetric cipher requires the cipher text to be (practically) indistinguishable from random. Length is not particularly useful (multiple blocks, different block ciphers with equal block length).
  - gcr 14y ago
    Lots of developers who read "Learn PHP in 24 Hours" and similar texts use md5 (32 chars) or sha1 (40 chars). If you're an attacker and see a hex string that's 40 chars long, that gives you a great place to start since you know it's likely to be a naïve SHA1 hash.
    - reyan 14y ago
      If Evernote is not using a key derivation function, I don't know what to say.
raverbashing 14y ago
No, it's usually known by the format, or even stored together with the password Example: crypt stored the password in the format: $id$salt$encrypted
- aadamov 14y ago
  But this is why we do one or both things: strip obvious things from hashed password and store them separately or add a trivial character reshuffling algorithm. The point is that hacker would not only have to steal your hashed passwords, but also steal and understand your code. Makes it more complicated.
  - raverbashing 14y ago
    No The security of your system can never depend on an attacker not knowing the implementation. Or: Security through obscurity (is no security) Using gimmicks like for example shuffling some characters in the hash may delay some attacks. But the problem is that these techniques are usually done on systems that have no sufficient security. Have a big salt and use PBKDF2 or Bcrypt and you know the exact difficulty of getting the passwords.
    - archivator 14y ago
      If you need a citable name, taking the transparency of the cryptosystem as an assumption is called Kerckhoffs's principle.
    - cschneid 14y ago
      IMO, you should be doing both. People should use strong bcrypted passwords, with a salt, then ALSO a 'secret' pepper value (long value stored in app code). This adds additional security in the case of a db-only dump being released, and doesn't harm the strength or a full code+db release at all either. Stripping off identifying info from hashes like talked about in this thread doesn't weaken the hash in any way, but instead makes it another thing to figure out by an attacker. At worse, you slow them down a bit, allowing you to do things like mass-email everybody affected. Security is about depth, not putting 100% of your trust in a single algorithm. Even if that algorithm is well trusted. It's simply not an either/or.
anonymfus 14y ago
For public service like Evernote attacker can usually create own accounts with known passwords before stealing database and then try to found algorithm and salt by brute force hashes against known password.

by NoPiece 14y ago

Curious, if the attacker knows what the encryption algorithm is, does it help them at all in breaking it? I.e., does it potentially delay breaking it by not revealing it?

UnoriginalGuy 14y ago

In theory, yes, in practice it is fairly obvious how something is hashed just by eye. Different hash algorithms produce different output (lengths, starting character, and spread). So with some experience you can often tell (or guess and test) what something is hashed with.

tobyjsullivan 14y ago
I would say that's not really true. The output hash will look the same if I apply a simple salted SHA-1 with a salt or if I apply 500 MD5's followed up followed up with 200 SHA-1's, each salted differently. I'm not a security expert, but I think this is closer to best practice these days. That said, revealing the exact algorithm would basically be throwing people with weak passwords to the wolves while really only supplying the rest of us with a false sense of security (because it will probably be cracked anyway). We'd also be better off if they didn't announce the algorithm if the passwords get leaked (like with LinkedIn).
- gcr 14y ago
  For practice, see if you can't identify the hashing algorithm for the following stored passwords: $6$AhHvI8ay$I0ED2wWVU9eheJKvCxzcbc/ZYRoN60q5XNHruYp8yFlQvEOjJ1WtIHUwjG6L4ZGntf3ei8osB7s2GYdkN01gx1 dGhpcyBpcyBzdHVwaWQKCg== 286755fad04869ca523320acce0dc6a4 some_salt:ac01346ad1553221506dd091800a1974 c8fed00eb2e87f1cee8e90ebbe870c190ac3848c 6b3a55e0261b0304143f805a24924d0c1c44524821305f31d9277843b8a10f4e /5L0cR/wpFqSA Note how they don't look the same, so it's quite easy for an attacker to tell the difference. Want to see how you did? Here's the answer key, in base64: MTogTW9kZXJuIGNyeXB0LCBsaWtlIHRoZSBraW5kIHlvdSdkIGZpbmQgaW4gL2V0Yy9zaGFkb3cK MjogSnVzdCBiYXNlNjRpbmcgdGhlIHJhdyBwYXNzd29yZCAoc3R1cGlkKQozOiBVbnNhbHRlZCBt ZDVzdW0KNDogbWQ1c3VtLCB3aXRoIHNhbHQgcHJlcGVuZGVkCjU6IFVuc2FsdGVkIHNoYTFzdW0K NjogVW5zYWx0ZWQgc2hhMjU2c3VtCjc6IE9sZCBVTklYIGNyeXB0KCk=
reyan 14y ago
The definition of a symmetric cipher requires the cipher text to be (practically) indistinguishable from random. Length is not particularly useful (multiple blocks, different block ciphers with equal block length).
- gcr 14y ago
  Lots of developers who read "Learn PHP in 24 Hours" and similar texts use md5 (32 chars) or sha1 (40 chars). If you're an attacker and see a hex string that's 40 chars long, that gives you a great place to start since you know it's likely to be a naïve SHA1 hash.
  - reyan 14y ago
    If Evernote is not using a key derivation function, I don't know what to say.

raverbashing 14y ago

No, it's usually known by the format, or even stored together with the password Example: crypt stored the password in the format: $id$salt$encrypted

aadamov 14y ago
But this is why we do one or both things: strip obvious things from hashed password and store them separately or add a trivial character reshuffling algorithm. The point is that hacker would not only have to steal your hashed passwords, but also steal and understand your code. Makes it more complicated.
- raverbashing 14y ago
  No The security of your system can never depend on an attacker not knowing the implementation. Or: Security through obscurity (is no security) Using gimmicks like for example shuffling some characters in the hash may delay some attacks. But the problem is that these techniques are usually done on systems that have no sufficient security. Have a big salt and use PBKDF2 or Bcrypt and you know the exact difficulty of getting the passwords.
  - archivator 14y ago
    If you need a citable name, taking the transparency of the cryptosystem as an assumption is called Kerckhoffs's principle.
  - cschneid 14y ago
    IMO, you should be doing both. People should use strong bcrypted passwords, with a salt, then ALSO a 'secret' pepper value (long value stored in app code). This adds additional security in the case of a db-only dump being released, and doesn't harm the strength or a full code+db release at all either. Stripping off identifying info from hashes like talked about in this thread doesn't weaken the hash in any way, but instead makes it another thing to figure out by an attacker. At worse, you slow them down a bit, allowing you to do things like mass-email everybody affected. Security is about depth, not putting 100% of your trust in a single algorithm. Even if that algorithm is well trusted. It's simply not an either/or.

anonymfus 14y ago

For public service like Evernote attacker can usually create own accounts with known passwords before stealing database and then try to found algorithm and salt by brute force hashes against known password.