EXC_BAD_ACCESS on CCHmac - iphone

Question

i am doing HMAC-SHA256 encoding . Tried but didn't find any solutions.
#include <CommonCrypto/CommonHMAC.h>
- (NSString *)hmacWithKey:(NSString *)key andData:(NSString *)data
{
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
///////////////////////////////////////////////////////////////
////but on below line of code i am getting EXC_BAD_ACCESS//////
///////////////////////////////////////////////////////////////
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
//////////////////////////////////////////////
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);
return hash;
}
Please tell me whats wrong i am doing here.
Thanks

Answer 1

cStringUsingEncoding:NSASCIIStringEncoding can return NULL if the string contains non-ASCII characters.
Therefore you should check if cKey == NULL or cData == NULL.
Or better, convert to UTF-8 strings:
const char *cKey = [key UTF8String];
const char *cData = [data UTF8String];

Answer 2

I ran the OPs code with sample strings with no error so the error must be in the input. Either one or more of the inputs is nil or non-ascii.
Please provide sample input that fails.
BTW, it is not necessary to use char strings, here is an example using NSData:
NSData *cKey = [key dataUsingEncoding:NSUTF8StringEncoding];
NSData *cData = [data dataUsingEncoding:NSUTF8StringEncoding];
NSMutableData *out = [NSMutableData dataWithLength:CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey.bytes, cKey.length, cData.bytes, cData.length, out.mutableBytes);
NSLog(#"out: %#", out);