MD5 algorithm in Objective-C

Question

How to calculate the MD5 in Objective-C?

Solution 1

md5 is available on the iPhone and can be added as an addition for ie NSString and NSData like below.

MyAdditions.h

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

@interface NSData (MyAdditions)
- (NSString*)md5;
@end

MyAdditions.m

#import "MyAdditions.h"
#import <CommonCrypto/CommonDigest.h> // Need to import for CC_MD5 access

@implementation NSString (MyAdditions)
- (NSString *)md5
{
    const char *cStr = [self UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, (int)strlen(cStr), result ); // This is the md5 call
    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]
        ];  
}
@end

@implementation NSData (MyAdditions)
- (NSString*)md5
{
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5( self.bytes, (int)self.length, result ); // This is the md5 call
    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]
        ];  
}
@end

EDIT

Added NSData md5 because I needed it myself and thought this is a good place to save this little snippet...

These methods are verified using the NIST MD5 test vectors in http://www.nsrl.nist.gov/testdata/

Solution 2

You can use the built-in Common Crypto library to do so. Remember to import:

#import <CommonCrypto/CommonDigest.h>

and then:

- (NSString *) md5:(NSString *) input
{
    const char *cStr = [input UTF8String];
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, strlen(cStr), digest ); // This is the md5 call

    NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];

    for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
    [output appendFormat:@"%02x", digest[i]];

    return  output;
}

Solution 3

If performance is important, you can use this optimized version. It is about 5 times faster than the ones with stringWithFormat or NSMutableString.

This is a category of NSString.

- (NSString *)md5
{
    const char* cStr = [self UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5(cStr, strlen(cStr), result);

    static const char HexEncodeChars[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
    char *resultData = malloc(CC_MD5_DIGEST_LENGTH * 2 + 1);

    for (uint index = 0; index < CC_MD5_DIGEST_LENGTH; index++) {
        resultData[index * 2] = HexEncodeChars[(result[index] >> 4)];
        resultData[index * 2 + 1] = HexEncodeChars[(result[index] % 0x10)];
    }
    resultData[CC_MD5_DIGEST_LENGTH * 2] = 0;

    NSString *resultString = [NSString stringWithCString:resultData encoding:NSASCIIStringEncoding];
    free(resultData);

    return resultString;
}

Solution 4

Any reason not to use the Apple implementation: https://developer.apple.com/library/mac/documentation/Security/Conceptual/cryptoservices/GeneralPurposeCrypto/GeneralPurposeCrypto.html#//apple_ref/doc/uid/TP40011172-CH9-SW1

Search for Cryptographic Services Guide on Apple developer site.

View more solutions

Comments

[openfrog]

Does this pull the entire file into memory?

[Klaas]

This is not about files. If you want to create a MD5 from a file with these methods, then you can do NSData *fileContents = [NSData dataWithContentsOfFile:@"<yourPath>"]; NSString *myHash = [fileContents md5]; And yes, this would pull the whole file into memory. If you find a solution that works with file streams, please post it as an answer.

[Nickolay Olshevsky]

If you need to hash file, you should use CC_MD5_Init, then CC_MD5_Update for all file data, and after that - CC_MD5_Finish.

[MaxGabriel]

Compiling for a 64 bit architecture, the call to strlen yields the warning: "Implicit conversion loses integer precision: 'unsigned long' to 'CC_LONG' (aka 'unsigned int')"

[Nilesh Kumar]

I implemented the above code but while running the application it's crashing(CC_MD5( cStr, strlen(cStr), digest )---->this line is throwing exception saying EXC_BAD_ACCESS)

[xyzzycoder]

The code that Joel published has a race condition, and it looks like yours may inherit it. See the comment that I published on Joel's post. joel.lopes-da-silva.com/2010/09/07/…

[Widerberg]

Thanks! Patched it up now. This was never a problem for me since in the original implementation, I always ran it in a dedicated thread ;)

[brandonscript]

@wimcNilesh check for self before executing; if self is nil, it'll crash.

[brandonscript]

This answer is a lot cleaner to read than the others; one thing it needs is a cast to (int) before strlen e.g. (int)strlen...

[Ayaz]

Hay This is nice +1 upvote, And can you please also provide md5 Decryption method same as your's encryption.

[zaph]

The link covers Common Crypto which most of the answers here utilize.

[vpathak]

Sure the algo is same. But note that implementing your own crypto algorithm can introduce flaws. It takes a lot of hardening to get it correct in all the scenarios. So using the library version is to be preferred, in the common case.

[albanx]

@Ayaz MD5 cannot be decrypt (at least simply with a method).

[Goles]

Just to point a detail out, but you should be returning [output copy]; , otherwise you're actually returning an NSMutableString.

[nonickname]

No visible @interface for 'ViewController' declares the selector 'UTF8String' any suggestions?

[seeker12]

@neo999 - Looks like you're trying to call the UTF8String method on a UIViewController instance. In the code above, @epatel implements an instance method, md5 in a category on the NSString class. So an instance of NSString, let's say myString with a value of "Hello, World!" would be called like so: [myString md5], and then the md5 method would return "65a8e27d8879283831b664bd8b7f0ad4".

[seeker12]

@Ayaz - MD5 is a 128-bit cryptographic hash function by design (Ronald Rivest 1991) but has since been found to be cryptographically broken. However, a cryptographic hash function, known as a "one-way function", is useful precisely because it cannot be "decrypted". It is designed to take an input of arbitrary length, e.g. a text document, and output a fixed-length hash value. So an original input can be hashed with the same function and compared to the hash of an input in question; if the two outputs are exactly the same, the original input has certainly been unmodified.