Objective-C sample code for HMAC-SHA1

Question

I need to generate HMAC-SHA1 in Objective C. But i didnt find anything that works. I tried with CommonCrypto, using CCHMAC, but didnt works. I need to generate a hmac and after generate HOTP number.

Somebody have any example code in Objective C or C?

Answer 1

Here's how you generate an HMAC using SHA-256:

NSString *key;
NSString *data;

const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];

unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];

CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC
                                      length:sizeof(cHMAC)];

NSString *hash = [HMAC base64Encoding];

I'm not aware of an HOTP library, but the algorithm was quite simple, if I recall correctly.

Answer 2

here is how you can generate HMAC-SHA1 base64.

You need to add Base64.h and Base64.m to your project. You can get it from here.

If you use ARC, it will show some errors in Base64.m. Find the lines who are similar like this

return [[[self alloc] initWithBase64String:base64String] autorelease];

what you need is to delete the autorelease section. The final result should look like:

return [[self alloc] initWithBase64String:base64String];

Now in your general project import "Base64.h" and the following code

#import "Base64.h"
#include <CommonCrypto/CommonDigest.h>
#include <CommonCrypto/CommonHMAC.h>

- (NSString *)hmacsha1:(NSString *)data secret:(NSString *)key {

    const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
    const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];

    unsigned char cHMAC[CC_SHA1_DIGEST_LENGTH];

    CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

    NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];

    NSString *hash = [HMAC base64String];

    return hash;
}

With

NSLog(@"Hash: %@", hash);  

you will get something similar to this:

ghVEjPvxwLN1lBi0Jh46VpIchOc=

 

Answer 3

This is the complete solution which works without any extra libraries or hacks:

+(NSString *)hmac:(NSString *)plainText withKey:(NSString *)key
{
    const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
    const char *cData = [plainText cStringUsingEncoding:NSASCIIStringEncoding];

    unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];

    CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

    NSData *HMACData = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];

    const unsigned char *buffer = (const unsigned char *)[HMACData bytes];
    NSString *HMAC = [NSMutableString stringWithCapacity:HMACData.length * 2];

    for (int i = 0; i < HMACData.length; ++i)
        HMAC = [HMAC stringByAppendingFormat:@"%02lx", (unsigned long)buffer[i]];

    return HMAC;
}

You don't have to include any third-party base64 library as it is already encoded.

Answer 4

This works without using custom protocols, using some code from http://cocoawithlove.com/2009/07/hashvalue-object-for-holding-md5-and.html

HashSHA256.h

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

@interface HashSHA256 : NSObject {


}

 - (NSString *) hashedValue :(NSString *) key andData: (NSString *) data ; 

@end

HashSHA256.m

#import "HashSHA256.h"

#import <CommonCrypto/CommonHMAC.h>


@implementation HashSHA256


- (NSString *) hashedValue :(NSString *) key andData: (NSString *) data {


    const char *cKey  = [key cStringUsingEncoding:NSUTF8StringEncoding];
    const char *cData = [data cStringUsingEncoding:NSUTF8StringEncoding];
    unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

    NSString *hash;

    NSMutableString* output = [NSMutableString   stringWithCapacity:CC_SHA256_DIGEST_LENGTH * 2];

    for(int i = 0; i < CC_SHA256_DIGEST_LENGTH; i++)
        [output appendFormat:@"%02x", cHMAC[i]];
    hash = output;
    return hash;

}

@end

Usage:

- (NSString *) encodePassword: (NSString *) myPassword {
    HashSHA256 * hashSHA256 = [[HashSHA256 alloc] init];   
    NSString * result = [hashSHA256 hashedValue:mySecretSalt andData:myPassword];       
    return result;       
}

Answer 5

This is how yo do it without external files returning an hex string:

-(NSString *)hmac:(NSString *)plaintext withKey:(NSString *)key
{
    const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
    const char *cData = [plaintext cStringUsingEncoding:NSASCIIStringEncoding];
    unsigned char cHMAC[CC_SHA1_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
    NSData *HMACData = [NSData dataWithBytes:cHMAC length:sizeof(cHMAC)];
    const unsigned char *buffer = (const unsigned char *)[HMACData bytes];
    NSMutableString *HMAC = [NSMutableString stringWithCapacity:HMACData.length * 2];
    for (int i = 0; i < HMACData.length; ++i){
        [HMAC appendFormat:@"%02x", buffer[i]];
     }
   return HMAC;
}

It was tested in xCode 5 with iOS 7 and works fine!

Answer 6

Out of interest, why do you create (unsigned char cHMAC) and then convert into (NSData) and then convert it into (NSMutableString) and then convert finally into (HexString)?

You could do this in a quicker way by cutting the middleman (i.e. without NSData and NSMutableString altogether, quicker and better performance), also changing (unsigned char) into (uint8_t []), after all they are all hex-arrays anyway!, below:

-(NSString *)hmac:(NSString *)plaintext withKey:(NSString *)key
{
const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [plaintext cStringUsingEncoding:NSASCIIStringEncoding];

uint8_t cHMAC[CC_SHA1_DIGEST_LENGTH];

CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

NSString *Hash1 = @"";
for (int i=0; i< CC_SHA1_DIGEST_LENGTH; i++)
{
    Hash1 = [Hash1 stringByAppendingString:[NSString stringWithFormat:@"%02X", cHMAC[i]]];
}
return Hash1;
}

I hope this helps,

Regards

Heider Sati

Answer 7

I spend a whole day, trying to convert the generated hash (bytes) into readable data. I used the base64 encoded solution from the answer above and it didn´t work at all for me (b.t.w. you need and an external .h to be able to use the base64 encoding, which I had).

So what I did was this (which works perfectly without an external .h):

CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

// Now convert to NSData structure to make it usable again
NSData *out = [NSData dataWithBytes:cHMAC length:CC_SHA256_DIGEST_LENGTH];

// description converts to hex but puts <> around it and spaces every 4 bytes
NSString *hash = [out description];
hash = [hash stringByReplacingOccurrencesOfString:@" " withString:@""];
hash = [hash stringByReplacingOccurrencesOfString:@"<" withString:@""];
hash = [hash stringByReplacingOccurrencesOfString:@">" withString:@""];
// hash is now a string with just the 40char hash value in it
NSLog(@"%@",hash);

Answer 8

Have you seen Jens Alfke's new MyCrypto classes?

He has some sample code on his blog.