iOS Generate Token

#include <CommonCrypto/CommonDigest.h>
#include <CommonCrypto/CommonHMAC.h>

+(NSString*)generateSignature:(NSString*) dataToEncrypt{

    NSString *key = UserSecretKey;
    NSString *data = dataToEncrypt;
    
    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 *nsdata = [NSData dataWithBytes:cHMAC length:CC_SHA256_DIGEST_LENGTH];
    
    NSUInteger capacity = [nsdata length] * 2;
    NSMutableString *stringBuffer = [NSMutableString stringWithCapacity:capacity];
    const unsigned char *dataBuffer = [nsdata bytes];
    NSInteger i;
    for (i=0; i<[nsdata length]; ++i) {
        [stringBuffer appendFormat:@"%02X", (NSUInteger)dataBuffer[i]];
    }
    
    return [stringBuffer lowercaseString];
}