Sha256 in Objective-C for iPhone - iphone

Question

When I use this code to create a sha256 of a string
unsigned char hashedChars[32];
NSString *inputString;
inputString = [NSString stringWithFormat:#"hello"];
NSData * inputData = [inputString dataUsingEncoding:NSUTF8StringEncoding];
CC_SHA256(inputData.bytes, inputData.length, hashedChars);
It returns the hash correctly, but I need to insert a string like this \x00\x25\x53 and in this case, the function returns a sha256 of empty string because the specified encoding cannot be used to convert the receiver.
Now, my question is:How to insert this special characters for generate a correct hash? Thanks

Answer 1

Try this, it worked for me
1) To get a hash for plain 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;
}

Answer 2

It's important to know that you need to import:
#import <CommonCrypto/CommonDigest.h>
Hope this help!

Answer 3

You probably should use NSData instead of NSString then. Where do you get that string from?

Answer 4

Some one looking the solution in Swift 3.0. here is
extension String {
// MARK: - SHA256
func get_sha256_String() -> String {
guard let data = self.data(using: .utf8) else {
print("Data not available")
return ""
}
return getHexString(fromData: digest(input: data as NSData))
}
private func digest(input : NSData) -> NSData {
let digestLength = Int(CC_SHA256_DIGEST_LENGTH)
var hashValue = [UInt8](repeating: 0, count: digestLength)
CC_SHA256(input.bytes, UInt32(input.length), &hashValue)
return NSData(bytes: hashValue, length: digestLength)
}
private func getHexString(fromData data: NSData) -> String {
var bytes = [UInt8](repeating: 0, count: data.length)
data.getBytes(&bytes, length: data.length)
var hexString = ""
for byte in bytes {
hexString += String(format:"%02x", UInt8(byte))
}
return hexString
}}
How to Use it
let signatures = "yourStringToBeConverted".get_sha256_String()
also don't forgot to import #import <CommonCrypto/CommonHMAC.h> in your Bridging-Header.h