In one of the projects at my work, I got task to verify some data (in migration process from old system to new one); one of the fields was Chilean RUT (Rol Único Tributario) or Tax Identification Number.
The RUT has 8 digits plus a validation number or letter (xx.xxx.xxx-z) and algorithm for verification (as per my knowledge) is as follows:
- Remove all characters except digits and last char which can be digit or letter “K”
- Pad with zeros (“0”) string until it is exactly 9 symbols long
- Multiply, from left to right, first 8 digits with following factors: 3, 2, 7, 6, 5, 4, 3, 2 and sum those results (let’s call it total)
- Find difference: 11 – (total % 11) (let’s call it rest)
- Determine control char by:
-
5.1 If rest = 11, than control char “0” (zero)
5.2 If rest = 10, than control char “K”
5.3 Otherwise, rest is control char - If the original control char (9th char) is equal to calculated control char, RUT is valid.
C# code for this could be like this:
/// <summary> /// Routine for checking of RUT correctness /// </summary> /// <param name="rut">RUT to check</param> /// <returns>true if RUT is valid</returns> /// <remarks>Only numbers and optional "K" at the end of string are expected /// </remarks> public static bool IsRutOk(string rut) { const string RutRegex = "[0-9]+K?"; Regex RegExRut = new Regex(RutRegex, RegexOptions.Compiled | RegexOptions.IgnoreCase); int[] coefs = {3, 2, 7, 6, 5, 4, 3, 2}; // In case that rut is padded with spaces rut = rut.Trim().ToUpperInvariant(); if (!RegExRut.IsMatch(rut)) { return false; } if (rut.Length > 9) { return false; } // If shorter than 9 characters (8 + control char) ... while (rut.Length < 9) { rut = "0" + rut; } int total = 0; for (int index = 0; index < rut.Length - 1; index++) { char curr = rut.Substring(index, 1).ToCharArray()[0]; total += coefs[index]*(curr - '0'); } int rest = 11 - (total%11); if (rest == 11) rest = 0; if ((rest == 10) && rut.EndsWith("K")) { return true; } if (rut.Substring(rut.Length - 1, 1).ToCharArray()[0] == ('0' + rest)) { return true; } return false; }
In a recent ASP.NET project, we had to replace 
Some security updates are not just security updates.
