(Objective-C) AES 256-bit CBC using PBKDF2 Generated Secret Key

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First generates a 32-byte secret key using PBKDF2 (with HMAC-SHA256), and then uses the secret key to do 256-bit AES CBC mode decryption.

(Duplicates the following Java code)

public String decrypt(String strToDecrypt) {
        try  {
            // Read the initialization vector from the first bytes for the data
            byte [] rawData = Base64.getDecoder().decode(strToDecrypt);
            byte [] iv = new byte[Config.get().encryptionIVLength()];
            byte [] encryptedData = new byte[rawData.length - iv.length];
            System.arraycopy(rawData, 0, iv, 0, iv.length);
            System.arraycopy(rawData, iv.length, encryptedData, 0, encryptedData.length);
 
            IvParameterSpec ivspec = new IvParameterSpec(iv);
 
            SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
            KeySpec spec = new PBEKeySpec(secretKey.toCharArray(), salt.getBytes(), 65536, 256);
            SecretKey tmp = factory.generateSecret(spec);
            SecretKeySpec secretKey = new SecretKeySpec(tmp.getEncoded(), "AES");
 
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            cipher.init(Cipher.DECRYPT_MODE, secretKey, ivspec);
            return new String(cipher.doFinal(encryptedData));
        }
        catch (Exception e) {
            log.error("Could not decrypt the string.", e);
        }
        return null;
    }

Chilkat Objective-C Library Downloads MAC OS X (Cocoa) Libs iOS Libs

#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 = @"some arbitrary length password";
// We have 8 bytes of salt encoded using hex.
// (The salt can be any number of bytes, in any desired encoding such as base64, hex, etc.)
NSString *saltHex = @"0102030405060708";

// Generate the 256-bit (32-byte) AES secret key we'll use to decrypt.
int iterationCount = 65536;
int outputKeyBitLen = 256;
NSString *secretKeyHex = [crypt Pbkdf2: password charset: @"utf-8" hashAlg: @"sha256" salt: saltHex iterationCount: [NSNumber numberWithInt: iterationCount] outputKeyBitLen: [NSNumber numberWithInt: outputKeyBitLen] encoding: @"hex"];

// Setup for 256-bit AES CBC decryption.
crypt.CryptAlgorithm = @"aes";
crypt.KeyLength = [NSNumber numberWithInt:256];
crypt.CipherMode = @"cbc";
crypt.PaddingScheme = [NSNumber numberWithInt:0];

// The IV for AES is 16 bytes.
NSString *iv = @"000102030405060708090A0B0C0D0E0F";
[crypt SetEncodedIV: iv encoding: @"hex"];

// Set the secret key for 256-bit AES.
[crypt SetEncodedKey: secretKeyHex encoding: @"hex"];

// AES decrypt
// assume our string to decrypt is base64
NSString *strToDecrypt = @"....";
crypt.EncodingMode = @"base64";
NSString *decryptedStr = [crypt DecryptStringENC: strToDecrypt];

NSLog(@"%@",decryptedStr);