Using MD5 hash on a string in cocoa?

Question

Possible Duplicate:
MD5 algorithm in Objective C

I need to hash a string using the MD5 technique in cocoa. Any frameworks that are used must be able to be accessed on the iphone. please provide code if possible.

Answer 1

Noticed this in the Facebook Connect source code. Looks pretty solid, give it a shot.

#import <CommonCrypto/CommonDigest.h>

...

+ (NSString*)md5HexDigest:(NSString*)input {
    const char* str = [input UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5(str, strlen(str), result);

    NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH*2];
    for(int i = 0; i<CC_MD5_DIGEST_LENGTH; i++) {
        [ret appendFormat:@"%02x",result[i]];
    }
    return ret;
}
...

Answer 2

Well, first off, MD5 isn't encryption. So if you're looking for encryption, you're looking in the wrong place.

But if you just want to hash something using MD5 on an iPhone, this should give you the information you need:

#import <CommonCrypto/CommonDigest.h>

NSString *md5(NSString *str) {
    const char *cStr = [str UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, strlen(cStr), result );
    return [NSString stringWithFormat:@"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
        result[0], result[1],
        result[2], result[3],
        result[4], result[5],
        result[6], result[7],
        result[8], result[9],
        result[10], result[11],
        result[12], result[13],
        result[14], result[15]
    ];
}

//…

NSString *digest = md5(@"test");
NSLog(@"MD5 TEST %@", digest);

(From Calculate MD5 on iPhone)

Answer 3

This is what I use. Credits go to Alistair McMillan.

#import <CommonCrypto/CommonDigest.h>


+ (NSString *) md5:(NSString *)str {
 const char *cStr = [str UTF8String];
 unsigned char result[16];
 CC_MD5( cStr, strlen(cStr), result );
 return [NSString stringWithFormat:
  @"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
  result[0], result[1], result[2], result[3], 
  result[4], result[5], result[6], result[7],
  result[8], result[9], result[10], result[11],
  result[12], result[13], result[14], result[15]
  ]; 
}

NOTE #1: I didn't have to link to any libraries

NOTE #2: I couldn't find -lcrypto in the external framework list on the iphone, and this works without -lcrypto

Answer 4

It's worth mentioning that the OpenSSL methods are deprecated on more recent versions of OS X, and the MD5 digest is conventionally lower case. Personally I'm more a fan of the unrolled style for efficiency, and I think using ObjC categories for this is a better fit.

For MD5Digest.h: #include

@interface NSString (MD5Digest)
- (NSString*) md5Digest;
@end

@interface NSData (MD5Digest)
- (NSString*) md5Digest;
@end

And MD5Digest.m:

#include <CommonCrypto/CommonDigest.h>
#include "MD5Digest.h"

static NSString* md5Digest(const void *data, CC_LONG length)
{
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    unsigned char* d = CC_MD5(data, length, digest);

    return [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
        d[0], d[1], d[2], d[3], d[4], d[5], d[6], d[7], d[8], d[9], d[10], d[11], d[12], d[13], d[14], d[15],
        nil];
}

@implementation NSString (MD5Digest)

- (NSString*) md5Digest
{
    return md5Digest([self UTF8String], [self lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
}

@end

@implementation NSData (MD5Digest)

- (NSString*) md5Digest
{
    return md5Digest([self bytes], [self length]);
}

@end

Answer 5

I added the following to my "NSString+MyGoonk" category:

#include <openssl/md5.h>

- (NSString *)md5
{
    NSData *data = [self dataUsingEncoding: NSUTF8StringEncoding];
    unsigned char *digest = MD5([data bytes], [data length], NULL);
    return [NSString stringWithUTF8String: (char *)digest];
}

Two things:

1. this assumes your string is UTF8. I'm sure there's a way to make it more generic, but I almost never use anything else.

2. you have to link -lcrypto into your project.

Answer 6

After spending too much time trying to figure this out I made a comprehensive post with correct code and how to use it. You can find the post here on my blog. http://www.saobart.com/md5-has-in-objective-c/

Answer 7

MD5 is not encryption, it is a cryptographic hash function. It's a one-way function whose output is a 128-bit number. The fact that it is cryptographic means that it is a computationally hard problem that, given an MD5 hash output, compute a string whose MD5 is that value. So, MD5 can be used for data integrity checks, but not for encryption.