HMAC-SHA256.m

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

#import "ViewController.h"

@implementation ViewController

- (NSData *)dataFromHexString:(NSString *)sHex {
	const char *chars = [sHex UTF8String];
	int i = 0;
	NSUInteger len = sHex.length;
	
	NSMutableData *data = [NSMutableData dataWithCapacity:len / 2];
	char byteChars[3] = {'\0','\0','\0'};
	unsigned long wholeByte;
	
	while (i < len) {
		byteChars[0] = chars[i++];
		byteChars[1] = chars[i++];
		wholeByte = strtoul(byteChars, NULL, 16);
		[data appendBytes:&wholeByte length:1];
	}
	
	return data;
}

- (NSData *)hmacForHexKey:(NSString *)hexkey andStringData:(NSString *)data
{
	
	NSData *keyData = [self dataFromHexString:hexkey];
	
	const char *cKey  = [keyData bytes];
	const char *cData = [data cStringUsingEncoding:NSUTF8StringEncoding];
	
	unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
	
	CCHmac(kCCHmacAlgSHA256, cKey, keyData.length, cData, strlen(cData), cHMAC);
	
	return [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];

}

- (NSData *)hmacForKey:(NSString *)key andStringData:(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);
	
	return [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
	
}

- (void)viewDidLoad {
	[super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.

	NSString *key = @"This is my random key.";
	NSString *hexKey = @"54686973206973206d792072616e646f6d206b65792e";
	
	NSString *data = @"This is a data string.";
	
	NSData *hmac1 = [self hmacForKey:key andStringData:data];
	NSLog(@"hmacForKey   : %@", hmac1);
	
	NSData *hmac2 = [self hmacForHexKey:hexKey andStringData:data];
	NSLog(@"hmacForHexKey: %@", hmac2);
}