4 ms·

Nitpick: this statement is not exactly true: "Hashes are designed to be tamper-proof". This only applies to cryptographic hash functions, like SHA-1 and Skein.

by exDM69 15y ago

Nitpick: this statement is not exactly true: "Hashes are designed to be tamper-proof". This only applies to cryptographic hash functions, like SHA-1 and Skein. There are non-cryptogaphic hash functions which are not designed to be secure, like Dan Bernstein's DJB-family of hashes (DJBX33A and DJBX33X), that are used e.g. for hash tables with string keys.

codinghorror 15y ago
I suppose I was thinking of Java and .NET where you don't generally get the chance to "pick" a hash function unless you're in the Crypto namespaces. There are certainly hash-based data structures like HashTables and the like, but the underlying hash algorithms are not exposed in any way, they're just magic.
- marcusf 15y ago
  Not to pile on with the nitpicking, but for just the cases everybody here is talking about (eg non-crypto hashing) you get to "pick" exactly the hash function. You're forced, actually, to implement hashCode() in Java if you want to be able to put the object in a HashMap, HashSet, etc.
  - canop_fr 15y ago
    You're right but that's still in a very small subset of possible hashing functions because you must produce a 4 bytes hash, which is then hashed again (to the length of the storage array). Of course you don't have as requirement to avoid collision, just to distribute as equally as possible.
- arethuza 15y ago
  You can override the default hash producing methods in both Java (hashCode) and C# (GetHashCode) - so while the standard hash generators might not be exposed directly they can easily be replaced.
- canop_fr 15y ago
  Using chosen hash functions in your applications isn't so rare even outside cryptography field. For example I often use hash for storage addressing (ala git). For this kind of thing you need something fast and with practically no collision (which isn't a requirement for a common hash table).

4 ms·

Nitpick: this statement is not exactly true: "Hashes are designed to be tamper-proof". This only applies to cryptographic hash functions, like SHA-1 and Skein.

by exDM69 15y ago

codinghorror 15y ago
I suppose I was thinking of Java and .NET where you don't generally get the chance to "pick" a hash function unless you're in the Crypto namespaces. There are certainly hash-based data structures like HashTables and the like, but the underlying hash algorithms are not exposed in any way, they're just magic.
- marcusf 15y ago
  Not to pile on with the nitpicking, but for just the cases everybody here is talking about (eg non-crypto hashing) you get to "pick" exactly the hash function. You're forced, actually, to implement hashCode() in Java if you want to be able to put the object in a HashMap, HashSet, etc.
  - canop_fr 15y ago
    You're right but that's still in a very small subset of possible hashing functions because you must produce a 4 bytes hash, which is then hashed again (to the length of the storage array). Of course you don't have as requirement to avoid collision, just to distribute as equally as possible.
- arethuza 15y ago
  You can override the default hash producing methods in both Java (hashCode) and C# (GetHashCode) - so while the standard hash generators might not be exposed directly they can easily be replaced.
- canop_fr 15y ago
  Using chosen hash functions in your applications isn't so rare even outside cryptography field. For example I often use hash for storage addressing (ala git). For this kind of thing you need something fast and with practically no collision (which isn't a requirement for a common hash table).