Question

I have a string of numbers that i would like to make shorter for use in a URL. This string always consists of numbers only. For example: 9587661771112

In theory, encrypting a numeric string into an alphanumeric(0-9a-zA-Z) string should always return a shorter result, which is what i want.

I’ve created an algorithm that does the following:

Encrypt ( string1 = numeric input string, string2 = alphanumeric return string)

• Takes the next two characters from string1 and converts them into a number, e.g 95 for the above example
• Checks if the number is less than 52(the combined length of a-z and A-Z)
  • if so, adds (“abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ”)[Number] to
    string2 and jump forward by 2 characters
  • else, add (“0123456789)[First digit of Number) to string2 and jump forward by 1 character

In the next step the number would be 58 and so on.

With some tweaking the shortest result i could get was: 9587661771112 > j9UQpjva

My problem is that with this technique, the result can vary dramaticaly. I also feel that this is not a clean solution to my problem.

So I need an encryption algorithm that converts a string of numbers into a shorter string of uppercase letters, lowercase letters and numbers. It has to be decryptable and have a more or less consistent result.

Any idea how to achieve this?

---

Solution:

string Chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

string Base10To62(long N)
{
    string R = "";
    while (N != 0)
    {
        R += Chars[(int)(N % 62)];
        N /= 62;
    }
    return R;
}

long Base62To10(string N)
{
    long R = 0;
    int L = N.Length;
    for (int i = 0; i < L; i++)
    {
        R += Chars.IndexOf(N[i]) * (long)Math.Pow(62, i);
    }
    return R;
}

works like a charm 🙂

Answer 1

Solution:

string Chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

    private static string Base10To62(string S) 
    {
        string R = "";
        var N = long.Parse(S);
        do { R += Chars[(int)(N % 0x3E)]; } while ((N /= 0x3E) != 0);
        return R;
    }

    private static string Base62To10(string S) 
    {
        long R = 0;
        int L = S.Length;
        for (int i = 0; i < L; i++) R += Chars.IndexOf(S[i]) * (long)(System.Math.Pow(0x3E, i));
        return R.ToString();
    }