SHA256 key generator in iphone - iphone

Question

I want to generate a key using SHA256 with N number of iterations.
They input should be my "password" + "random number"
I have seen the Crypto sample provided by apple but it seems it doesn't provide my requirement(or might be possible I didnt get it properly).
I have gone through below link as well but is doesnt have method to generate a key using SHA256
http://iphonedevelopment.blogspot.com/2009/02/strong-encryption-for-cocoa-cocoa-touch.html
Waiting for some hint.
Regards

Answer 1

Try this, it worked for me
1) To get a hash for plane text input
-(NSString*)sha256HashFor:(NSString*)input
{
const char* str = [input UTF8String];
unsigned char result[CC_SHA256_DIGEST_LENGTH];
CC_SHA256(str, strlen(str), result);
NSMutableString *ret = [NSMutableString stringWithCapacity:CC_SHA256_DIGEST_LENGTH*2];
for(int i = 0; i<CC_SHA256_DIGEST_LENGTH; i++)
{
[ret appendFormat:#"%02x",result[i]];
}
return ret;
}
2) To get hash for NSData as input
Note:- I have used NSData category, so the code is as follow
- (NSString *)SHA256_HASH {
if (!self) return nil;
unsigned char hash[CC_SHA256_DIGEST_LENGTH];
if ( CC_SHA256([(NSData*)self bytes], [(NSData*)self length], hash) ) {
NSData *sha2 = [NSData dataWithBytes:hash length:CC_SHA256_DIGEST_LENGTH];
// description converts to hex but puts <> around it and spaces every 4 bytes
NSString *hash = [sha2 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 = %#",hash);
// Format SHA256 fingerprint like
// 00:00:00:00:00:00:00:00:00
int keyLength=[hash length];
NSString *formattedKey = #"";
for (int i=0; i<keyLength; i+=2) {
NSString *substr=[hash substringWithRange:NSMakeRange(i, 2)];
if (i!=keyLength-2)
substr=[substr stringByAppendingString:#":"];
formattedKey = [formattedKey stringByAppendingString:substr];
}
return formattedKey;
}
return nil;
}