使用 java 解密 C# 中的 AES 加密文件

Question

I have the following problem. I use this code to encrypt a sample text in C#, and want to decrypt it in java. I use the following java code.

byte[] IV = { 65, 1, 2, 23, 4, 5, 6, 7, 32, 21, 10, 11, 12, 13, 84, 45 };
byte[] KEY = { 0, 42, 2, 54, 4, 45, 6, 7, 65, 9, 54, 11, 12, 13, 60, 15 };
byte baData[] = new byte[1024];
int iRead = 0;

SecretKeySpec key = new SecretKeySpec(KEY, "AES/CBC/PKCS5Padding");
Cipher cipher = Cipher.getInstance ("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(IV));

File file = new File("/sdcard", "SAMPLE.txt");

FileInputStream in = new FileInputStream(file);
iRead = in.read(baData, 0, baData.length);

String strResult = new String(cipher.doFinal(baData, 0, baData.length));

I obviously use the same IV and KEY values above as in the C# sample. The above java code runs on an android device, and the encrypted binary file is the SAMPLE.txt on it's sdcard. The problem is I don't get the correct data after decrypting it. Can anyone tell me what I'm doing wrong?

Thanks.

Answer 1

There are a few problems here:

• What encoding are you using to convert the text data into binary before encrypting it? Your current use of the string constructor will use the platform default encoding - almost never a good idea
• You're assuming that a single call to read() will read everything - you're not actually using the value of iRead later
• You're assuming that all the data will fit in a 1024-byte buffer

It's hard to know which of those is causing the problem.

I would strongly suggest that you use a CipherInputStream to wrap your FileInputStream , and then wrap an InputStreamReader around that, using the appropriate encoding. You could then use something like Guava's CharStreams.toString() method to read everything from the InputStreamReader into a string.

EDIT: As noted in comments, while all of these are potential problems, there's also the matter of the code currently creating the Cipher in encryption mode rather than decryption mode.