(Objective-C) Hashing Encoded Data

This example explains how it's important to know exactly what bytes are getting hashed when working with encoded data, such as hex, base64, etc.

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#import <CkoCrypt2.h>
#import <NSString.h>

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];

// Imagine we want to SHA-1 hash this A9133F6DC63E85BE0619763F8975CA076FF91B95CB6F121CD21C016143315E11B9ED4374F174B2CC
NSString *strToHash = @"A9133F6DC63E85BE0619763F8975CA076FF91B95CB6F121CD21C016143315E11B9ED4374F174B2CC";

// The question is:  Do we want to hash the bytes 0xA9, 0x13, 0x3F...
// or do we want to literally hash each us-ascii byte:  'A', '9', '1', '3'.

// The results will obviously be different depending on what bytes are actually hashed.

// To hash the decoded bytes (i.e. 0xA9, 0x13, 0x3F...) we do this:

// "hex" is not an actual character encoding.  It's a special value to be used to tell Chilkat to hex decode
// the string and pass the decoded bytes to the hash algorithm...
crypt.Charset = @"hex";
crypt.HashAlgorithm = @"sha1";
// Get the hash result in lowercase hex
crypt.EncodingMode = @"hex_lower";
NSString *hashValue = [crypt HashStringENC: strToHash];
NSLog(@"%@%@",@"hash of decoded hex bytes: ",hashValue);

// The result is 7a4a2ba73811fab98b4baaee2df164cbdd0d8e8e

// This is how to hash the us-ascii byte values:
// The Charset property defines the byte representation of the string passed to the hash algorithm:
crypt.Charset = @"us-ascii";
// The EncodingMode property defines the binary encoding (hex, base64, etc.) of the hash returned as an encoded string.
crypt.EncodingMode = @"hex";
crypt.HashAlgorithm = @"sha1";

hashValue = [crypt HashStringENC: strToHash];
NSLog(@"%@%@",@"hash of us-ascii bytes: ",hashValue);

// The result is:  2A7500F88734F4B19C79852CA0FF3E1C561F31C8

//