PHP encode methods

Question

Is it possible to encode user's ID# to text value?

For example if the user ID# is '50624' is it possible to convert it to 7 characters text value, something like 'DEGXCVG'?

If I use MD5 for this function I get 16-byte hash value. The result value should not be longer than 7 or 8 characters.

Edit: I want that each user has a different text code obtained from the id number.

Answer 1

Try changing the integer into a Hexadecimal value using dechex

Anyway if u able to explain your scenario more clear, we may able to provide best solution

Answer 2

What are you trying to accomplish with this?

First of all MD5 is not "encryption" it is a one-way hash function. It cannot be reversed. If that is OK for you, why not simply hash your IDs and then take 7-8 characters from the hash? You could MD5 your ID and then take the first 8 characters of the resulting MD5.

Answer 3

what you are looking for is called base transformation ... your ID is a base 10 number with the numbers from 0 to 9 represent the digits of that base.

other common bases would be 2 (binary), 16(hexadecimal), or 64(often called base 64 encoding) but you could also take some other base if you like.

i've written a somewhat general base transform code in c# (uint to whatever base string and vice versa) ... shouldn't be that hard to port it to php:

static void Main(string[] args)
{
    foreach (var item in UintToOtherBase(0xDEADBEEF, "01").Reverse())
    {
        Console.Write(item);
    }
    Console.WriteLine();
    Console.WriteLine(OtherBaseToInt(UintToOtherBase(0xDEADBEEF, "01"), "01").ToString("X"));
    Console.WriteLine(UintToOtherBase(0xDEADBEEF, "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"));
}

public static string UintToOtherBase(uint input, string newBaseDigits)
{
    char[] uniqueDigits = newBaseDigits.ToCharArray().Distinct().ToArray();
    uint newBase = (uint)uniqueDigits.Length;
    if (newBase < 2)
    {
        throw new ArgumentException("otherBaseDigits has to contain at least 2 unique chars");
    }
    else
    {
        StringBuilder sb = new StringBuilder();
        while (input != 0)
        {
            uint digit = input % newBase;
            sb.Append(uniqueDigits[digit]);
            input /= newBase;
        }
        return sb.ToString();
    }
}
public static uint OtherBaseToInt(string input, string otherBaseDigits)
{
    string uniqueDigits = new String(otherBaseDigits.ToCharArray().Distinct().ToArray());
    int otherBase = uniqueDigits.Length;
    if (otherBase < 2)
    {
        throw new ArgumentException("otherBaseDigits has to contain at least 2 unique chars");
    }
    else if (input.ToCharArray().Any(x => !uniqueDigits.Contains(x)))
    {
        throw new ArgumentException("an input char was not found in otherBaseDigits");
    }
    else
    {
        uint result = 0;
        int pow = 0;
        foreach (var c in input)
        {
            result += (uint)uniqueDigits.IndexOf(c) * (uint)Math.Pow(otherBase, pow++);
        }
        return result;
    }
}

//edit:

but just to point it out, this is an encoding ... no encryption

Answer 4

If a hash function such as MD5 can be used instead of encryption, you could try crc32() instead, which produces shorter (but with much higher chances of collisions) strings.

---

If you just care about encoding, you could do something simpler:

function encode($id) {
  $id_str = (string) $id;
  $offset = rand(0, 9);
  $encoded = chr(79 + $offset);
  for ($i = 0, $len = strlen($id_str); $i < $len; ++$i) {
    $encoded .= chr(65 + $id_str[$i] + $offset);
  }
  return $encoded;
}

function decode($encoded) {
  $offset = ord($encoded[0]) - 79;
  $encoded = substr($encoded, 1);
  for ($i = 0, $len = strlen($encoded); $i < $len; ++$i) {
    $encoded[$i] = ord($encoded[$i]) - $offset - 65;
  }
  return (int) $encoded;
}

Example:

var_dump(encode(50624)); // string(6) "TKFLHJ"

---

Encryption version:

define('CRYPTO_KEY', 'Secret key');

function encrypt($id) {
  return base64_encode(mcrypt_encrypt(MCRYPT_BLOWFISH, CRYPTO_KEY, (string) $id, MCRYPT_MODE_ECB));
}

function decrypt($encrypted) {
  return (int) base64_decode(mcrypt_decrypt(MCRYPT_BLOWFISH, CRYPTO_KEY, $encrypted, MCRYPT_MODE_ECB));
}

Answer 5

If obscuring is good enough, convert the number to base62 after permuting its bits.

Answer 6

I think you can design your own encryption method or take part of md5 hash value.
Btw, the way to encrypt an integer has been discussed in the following post.

Way to encrypt a single int