Video file decryption in iOS

Question

I have an application which gets encrypted video in compressed mode from a Java server. On the iOS side I'm not able to decrypt that. The code I using for encryption in Java is: ``` // generate a key KeyGenerator keygen = KeyGenerator.getInstance("AES"); keygen.init(128); // To use 256 bit keys, you need the "unlimited strength" encryption policy files from Sun. //byte[] key = keygen.generateKey().getEncoded(); byte key[] = {0x00, 0x01, 0x02, 0x11, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}; SecretKeySpec skeySpec = new SecretKeySpec(key, "AES"); SecureRandom random = new SecureRandom(); IvParameterSpec ivspec = new IvParameterSpec(key); // initialize the cipher for encrypt mode Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec, ivspec); System.out.println(); byte[] encrypted = cipher.doFinal(IOUtils.toByteArray(new FileInputStream(new File(fileName)))); ``` My code for decryption in iOS is the following:…

Accepted Answer

The password is not the correct length for `kCCAlgorithmAES128`, it is 88 bits:

```
NSData *passwordData = [@"[B@71e2b67c" dataUsingEncoding:NSUTF8StringEncoding];
```

There is an inconsistency:

`kCCAlgorithmAES128` and `kCCKeySizeAES256`

The decryption key is not the same as the encryption key. The decryption iv is not the same as the encryption iv.

Just for starters you need to get these correct.

As @Duncan writes, start with a very simple case and when that is working add complexity. A simple starting point is exactly one block of data, no padding, a simple key of the correct size, an iv of all 0s.

Best bet: hire a domain expert, security is very hard to get correct.

Video file decryption in iOS

Solution

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