IBAN Validator Swift
I am writing an algorithm to check IBAN (International Bank Account Number) in Swift 3 and cannot figure out one of the validations.
IBAN example - BE68539007547034
Here are the validation rules -
- The input number must be 16 in length.
- The first 2 characters are the country code (not numeric).
- The last 14 are numeric.
- The last 2 symbols are the result modulo 97 of the previous 12 digital symbols.
While # 1 - # 3 is clear, I need clarity in # 4. If anyone has done this before and found out about it, please let me know.
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5 answers
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")
seal
IBAN GB82WEST12345698765432 is valid
With the IBAN from your question it prints
IBAN BE68539007547034 is valid
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The validation algorithm is pretty 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]*$", options: .regularExpression) != nil else {
return false
}
return (uppercase.mod97() == 1)
}
}
Using:
let iban = "XX0000000..."
let valid = iban.passesMod97Check()
If you want to check the format for a specific country, just change the regex like
"^[A-Z]{2}[0-9]{14}$"
or directly
"^BE\\d{14}$"
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I found a great solution that works for me in Objective-C https://gist.github.com/0xc010d/5301790 you can rewrite for Swift or use bridge header. Objective-C implementation of the mod97 IBAN verification 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;
}
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