IBAN Validator Swift - ios

Question

I am writing an algorithm to validate IBAN (International Bank Account Number) in Swift 3 and not able to figure one of the validation.
Example IBAN - BE68539007547034
Here are the rules to validate -
Input number should be of length 16.
First 2 characters are country code (not numeric).
Last 14 are numeric.
Last 2 characters are the modulo 97 result of the previous 12 numeric characters.
While #1 - #3 are clear I need clarity on #4. If anyone have done this before and know about it then please let me know.

Answer 1

The validation algorithm is rather simple if you follow the algorithm on wikipedia:
extension String {
private func mod97() -> Int {
let symbols: [Character] = Array(self)
let swapped = symbols.dropFirst(4) + symbols.prefix(4)
let mod: Int = swapped.reduce(0) { (previousMod, char) in
let value = Int(String(char), radix: 36)! // "0" => 0, "A" => 10, "Z" => 35
let factor = value < 10 ? 10 : 100
return (factor * previousMod + value) % 97
}
return mod
}
func passesMod97Check() -> Bool {
guard self.characters.count >= 4 else {
return false
}
let uppercase = self.uppercased()
guard uppercase.range(of: "^[0-9A-Z]*$", options: .regularExpression) != nil else {
return false
}
return (uppercase.mod97() == 1)
}
}
Usage:
let iban = "XX0000000..."
let valid = iban.passesMod97Check()
If you want to validate the format for a specific country, just modify the regular expression, e.g.
"^[A-Z]{2}[0-9]{14}$"
or directly
"^BE\\d{14}$"

Answer 2

From Wikipedia
let IBAN = "GB82WEST12345698765432" // uppercase, no whitespace !!!!
var a = IBAN.utf8.map{ $0 }
while a.count < 4 {
a.append(0)
}
let b = a[4..<a.count] + a[0..<4]
let c = b.reduce(0) { (r, u) -> Int in
let i = Int(u)
return i > 64 ? (100 * r + i - 55) % 97: (10 * r + i - 48) % 97
}
print( "IBAN \(IBAN) is", c == 1 ? "valid": "invalid")
prints
IBAN GB82WEST12345698765432 is valid
With IBAN from your question it prints
IBAN BE68539007547034 is valid

Answer 3

I finded a great solution that work for me in Objective-C
https://gist.github.com/0xc010d/5301790 you can rewrite for Swift or use bridging header. Objective-C implementation of mod97 IBAN checking algorithm
#import <Foundation/Foundation.h>
#interface NSString (Mod97Check)
- (BOOL)passesMod97Check; // Returns result of mod 97 checking algorithm. Might be used to check IBAN.
// Expects string to contain digits and/or upper-/lowercase letters; space and all the rest symbols are not acceptable.
#end
#import "NSString+Mod97Check.h"
#implementation NSString (Mod97Check)
- (BOOL)passesMod97Check {
NSString *string = [self uppercaseString];
NSInteger mod = 0, length = [self length];
for (NSInteger index = 4; index < length + 4; index ++) {
unichar character = [string characterAtIndex:index % length];
if (character >= '0' && character <= '9') {
mod = (10 * mod + (character - '0')) % 97; // '0'=>0, '1'=>1, ..., '9'=>9
}
else if (character >= 'A' && character <= 'Z') {
mod = (100 * mod + (character - 'A' + 10)) % 97; // 'A'=>10, 'B'=>11, ..., 'Z'=>35
}
else {
return NO;
}
}
return (mod == 1);
}
#end
-(BOOL)isValidIBAN {
NSString *iban = self;
static NSString* const LettersAndDecimals = #"ABCDEFGHIJKLKMNOPQRSTUVWXYZ0123456789";
iban = [[iban stringByReplacingOccurrencesOfString:#" " withString:#""] uppercaseString];
NSCharacterSet *invalidChars = [[NSCharacterSet characterSetWithCharactersInString:LettersAndDecimals] invertedSet];
if ([iban rangeOfCharacterFromSet:invalidChars].location != NSNotFound)
{
return NO;
}
int checkDigit = [iban substringWithRange:NSMakeRange(2, 2)].intValue;
iban = [NSString stringWithFormat:#"%#%#",[iban substringWithRange:NSMakeRange(4, iban.length - 4)], [iban substringWithRange:NSMakeRange(0, 4)]] ;
for (int i = 0; i < iban.length; i++) {
unichar c = [iban characterAtIndex:i];
if (c >= 'A' && c <= 'Z') {
iban = [NSString stringWithFormat:#"%#%d%#", [iban substringWithRange:NSMakeRange(0, i)], (c - 'A' + 10),[iban substringWithRange:NSMakeRange(i+1, iban.length - i - 1)]];
}
}
iban = [[iban substringWithRange:NSMakeRange(0, iban.length - 2)] stringByAppendingString:#"00"];
while(true)
{
int iMin = (int)MIN(iban.length, 9);
NSString* strPart = [iban substringWithRange:NSMakeRange(0, iMin)];
int decnumber = strPart.intValue;
if(decnumber < 97 || iban.length < 3)
break;
int del = decnumber % 97;
iban = [NSString stringWithFormat:#"%d%#", del, [iban substringFromIndex:iMin]];
}
int check = 98 - iban.intValue;
return checkDigit == check;
}

Answer 4

Here you go :
func isValidIBAN(text:String) -> Bool {
let ibanRegEx = "[a-zA-Z]{2}+[0-9]{2}+[a-zA-Z0-9]{4}+[0-9]{7}([a-zA-Z0-9]?){0,16}"
let ibanTest = NSPredicate(format:"SELF MATCHES %#", ibanRegEx)
return ibanTest.evaluate(with: text)
}
It's clean, and it works.