CODEWITHSUNDEEP
c#encryptionhash
Ben Foster
Ben Foster

Reputation: 34800

Creating a unique URL safe hash

I want to hash/encode a unique integer (database ID) to create a similarly unique string.

It needs to meet the following requirements:

  1. Must start with a letter or number, and can contain only letters and numbers.
  2. All letters in a container name must be lowercase.
  3. Must be from 3 through 63 characters long (although the shorter the better)

The result does not need to be reversible, just repeatable - so a 1-way hash would be fine.

Upvotes: 1

Views: 3236

Answers (3)

Alexei Levenkov
Alexei Levenkov

Reputation: 100547

If you are fine with reversible (as Base36) than there is already built in Base16 (hex) formatting that probably would work too to slightly hide the number from regular people: String.Format("{0:x}", 1235) or 12345.ToString("x")

Upvotes: 1

CodesInChaos
CodesInChaos

Reputation: 108810

A simple solution would be a base 36 encoding. The output will be a string between one and six characters.

public static string EncodeBase36(int i)
{
  Contract.Requires<ArgumentException>(i>=0);
  //Base conversion
  string s="";
  while(i!=0)
  {
    int digit = i % 36;
    i/=36;
    if(digit<10)
      s=((char)('0'+digit)).ToString()+s;
    else
      s=((char)('a'+digit-10)).ToString()+s;
  }
  // Enforce minimum length
  while(s.Length<3)
  {
    s = "0" + s;
  }
  return s;
}

Upvotes: 4

akton
akton

Reputation: 14386

Is there a reason why you cannot use base 64 encoded MD5 using the MD5CryptoServiceProvider Class or SHA1 using the SHA1CryptoServiceProvider Class? I am not aware of a cryptanalysis of base 36 but I would guess the collision rate is probably better with MD5 or SHA1.

Upvotes: 1

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