padding error when decrypting data using AES-CBC-PKCS5Padding

Question

I wrote two functions as follows which encrypt and decrypt the data.

public static void encrypt() throws Exception {
    // Add the BouncyCastle Provider
    //Security.addProvider(new BouncyCastleProvider());


// Generate the key
byte[] keyBytes = "AAAAAAAAAAAAAAAA".getBytes();
SecretKeySpec   key = new SecretKeySpec(keyBytes, "AES");

// Generate the IV
byte[] ivBytes  = "AAAAAAAAAAAAAAAA".getBytes();
IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);

// Create the cipher object and initialize it
Cipher          cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);

// Read all bytes from a file into a bytes array
byte[] inputBytes = GCM.readFile("input");
byte[] cipherBytes = cipher.doFinal(inputBytes);

BufferedOutputStream  outputStream = new BufferedOutputStream(new FileOutputStream("output.enc"));
outputStream.write(cipherBytes);

outputStream.close();   
}

public static void decrypt() throws Exception {
    // Add the BouncyCastle Provider
     //Security.addProvider(new BouncyCastleProvider());

 // Generate the key
 byte[] keyBytes = "AAAAAAAAAAAAAAAA".getBytes();
 SecretKeySpec   key = new SecretKeySpec(keyBytes, "AES");

 // Generate the IV
 byte[] ivBytes  = "AAAAAAAAAAAAAAAA".getBytes();
 IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);

 // Create the cipher object and initialize it
 Cipher          cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
 cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);

 // Read all bytes from a file into a bytes array
 byte[] cipherBytes = GCM.readFile("ouput.enc");
 byte[] decBytes = cipher.doFinal(cipherBytes);

 BufferedOutputStream  outputStream = new BufferedOutputStream(new FileOutputStream("regen.plain"));
 outputStream.write(decBytes);
 outputStream.close();   
}

I realize that the code has the key set as "AAAAAAAAAAAAAAAA".getBytes() ; however please bear with me as this is just an example.

When I run the program I get the following stack trace :-

Exception in thread "main" javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher
    at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
    at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)
    at javax.crypto.Cipher.doFinal(DashoA13*..)
    at GCM.decrypt(GCM.java:80)
    at GCM.main(GCM.java:90)

I'm having trouble figuring out why I'm encountering this error. Any hints on how I could solve the issue?

[EDIT] It seems that when I write out data there are 16 bytes in all but only 15 bytes when I read it back in.

Answer 1

On your update: Well, that's easy then, fix the part that reads the file because the ciphertext needs to be N * blocksize, thus 16 bytes. I don't see any other blatant errors.

Answer 2

Possible problem (unless it is a typo) you write to output.enc but read from ouput.enc.