How do I create an MD5 Hash of a string in Cocoa?

Question

I know SHA-1 is preferred, but this project requires I use MD5.

#include 

- (NSString*) MD5Hasher: (NSString*) query {
    NSData* hash         


        

Answer 1

cdespinosa and irsk have already shown you your actual problem, so let me go through your GDB transcript:

(gdb) p digest
$1 = (unsigned char *) 0xa06310e4 "\0206b\260/\336\316^\021\b\a/9\310\225\204"

You've printed digest as a C string. You can see here that this string is raw bytes; hence all the octal escapes (e.g., \020, \225) and the couple of punctuation characters (/ and ^). It is not the printable ASCII hexadecimal representation you were expecting. You're lucky that there were no zero bytes in it; otherwise, you would not have printed the entire hash.

(gdb) po final
Cannot access memory at address 0x0

final is nil. This makes sense, as your string above isn't valid UTF-8; again, it's just raw data bytes. stringWithUTF8String: requires a UTF-8-encoded text string; you didn't give it one, so it returned nil.

For passing raw data around, you'd use NSData. In this case, I think you want the hex representation, so you'll need to create that yourself the way irsk showed you.

Finally, consider how lucky you are that your input didn't hash to a valid UTF-8 string. If it had, you wouldn't have noticed this problem. You may want to construct a unit test for this hash method with this input.

(gdb) po digest

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0xb0623630
0x98531ed7 in objc_msgSend ()

Your program crashed (specific problem: “bad access”, “invalid address”) in objc_msgSend. This is because digest either is not a Cocoa/CF object at all or was one but was freed. In this case, it's because digest is not a Cocoa object; it is a C array of bytes, as shown by your p digest line above.

Remember, Objective-C is a superset of C. All of C exists unchanged in it. That means there are C arrays (e.g., char []) and Cocoa's NSArrays side by side. Moreover, since NSArray comes from the Cocoa framework, not the Objective-C language, there's no way to make NSArray objects interchangeable with C arrays: You can't use the subscript operator on Cocoa arrays, and you can't send Objective-C messages to C arrays.

Answer 2

- (NSString*)MD5:(NSData *) data
    {
        // Create byte array of unsigned chars
        unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];

        // Create 16 byte MD5 hash value, store in buffer
        CC_MD5([data bytes], (CC_LONG)data.length, md5Buffer);

        // Convert unsigned char buffer to NSString of hex values
        NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
        for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
        [output appendFormat:@"%02x",md5Buffer[i]];

        return output;
    }

How to use

NSString *yourStrToBeConverted;
NSData* data = [yourStrToBeConverted dataUsingEncoding:NSUTF8StringEncoding];
NSString *md5res=[self MD5:data];

Answer 3

These answers are correct but confusing. I post a working sample, since I had issues with most other answers. The code is tested and works well for Mac OS X 10.12.x and iOS 10.1.x.

YourClass.h

#import <CommonCrypto/CommonDigest.h>
@interface YourClass : NSObject
+ (NSString *) md5:(NSString *) input;
@end

YourClass.m

#import YourClass.h

+ (NSString *) md5:(NSString *) input
{
    const char *cStr = [input UTF8String];
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    CC_MD5(cStr, (uint32_t)strlen(cStr), digest);
    NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
    for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
        [output appendFormat:@"%02x", digest[i]]; //%02X for capital letters
    return output;
}

Usage (e.g. in some other class):

SomeOtherClass.h

#import "YourClass.h"

SomeOtherClass.m

-(void) Test
{
    //call by [self Test] or use somewhere in your code.
    NSString *password = @"mypassword123";
    NSString *md5 = [YourClass md5:password];
    NSLog(@"%@", password);
    NSLog(@"%@", md5);
}