Extending the NSString class with a MD5 hex digest method using a category

md5test.m

#import <Foundation/Foundation.h>
#import "NSString+MD5HexDigest.h"
 
int main (int argc, const char * argv[])
{
  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
  NSString *str  = [NSString stringWithString:@"test"];
  NSString *md5;
 
  NSLog(@"String: %@", str);
  md5 = [str md5HexDigest];
  NSLog(@"MD5 Hash: %@",md5); /* Should be "098f6bcd4621d373cade4e832627b4f6" */ 
 
  [pool drain];
  return 0;
}

NSString+MD5HexDigest.h

#import <Cocoa/Cocoa.h>
#import <CommonCrypto/CommonDigest.h>

@interface NSString (md5)
-(NSString *) md5HexDigest;
@end

NSString+MD5HexDigest.m

#import "NSString+MD5HexDigest.h"

@implementation NSString (md5)
 
-(NSString *) md5HexDigest
{
   const char *original_str = [self UTF8String];
   unsigned char result[CC_MD5_DIGEST_LENGTH];
   CC_MD5(original_str, strlen(original_str), result);
   NSMutableString *hash = [NSMutableString string];
   for (int i = 0; i < 16; i++)
        [hash appendFormat:@"%02X", result[i]];
   return [hash lowercaseString];
}
 
@end