(Objective-C) Deriving a 256-bit AES Secret Key from a Password Using SHA256

This example demonstrates how to derive a 256-bit secret key for AES encryption from an password string. (A more secure way of deriving secret keys from passwords is via PBKDF2, and Chilkat has examples for this on example-code.com).

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

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

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

NSString *password = @"mySecretPassword";

crypt.EncodingMode = @"hex";

// We're going to hash the utf-8 byte representation of the password.
// For this example, the utf-8 byte representation is identical to the us-ascii 
// representation because there are no 8bit chars (such as non-English or chars with accent marks.)
crypt.Charset = @"utf-8";

// Compute the SHA-256 hash of the password, and return the hash
// in hexidecimal string form:
NSString *strSecretKeyHex = [crypt HashStringENC: password];

// Set our encryption algorithm to 256-bit AES (CBC mode)
crypt.CryptAlgorithm = @"aes";
crypt.CipherMode = @"cbc";
crypt.KeyLength = [NSNumber numberWithInt:256];
[crypt SetEncodedIV: @"000102030405060708090A0B0C0D0E0F" encoding: @"hex"];

// Now set the 256-bit binary secret key:
[crypt SetEncodedKey: strSecretKeyHex encoding: @"hex"];

// That's all for this example.  We've setup the encryptor with our
// 256-bit key derived from a password string.  There are other examples
// to show the calls for encrpyting / decrypting..