AES DEcryption in CTR mode (Java)

Question

I have these information:

CTR key: 36f18357be4dbd77f050515c73fcf9f2

CTR Ciphertext 1:69dda8455c7dd4254bf353b773304eec0ec7702330098ce7f7520d1cbbb20fc3\ 88d1b0adb5054dbd7370849dbf0b88d393f252e764f1f5f7ad97ef79d59ce29f5f51eeca32eabedd9afa9329

Note that the 16-byte encryption IV is chosen at random and is prepended to the ciphertext. And the text is encrypted with AES in CTR mode.

I have to discover the plaintext To do this I have written a short Java program but it doesn't work and I don't find why :/

This is the Java program

import java.nio.charset.Charset;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AES {

/**
 * @param args
 */
public static void main(String[] args) throws Exception {
    // TODO Auto-generated method stub

    //Dernier exemple CTR mode
    //Clé 16 bits 
    byte[] keyBytes = new byte[] { (byte)0x36,(byte)0xf1,(byte)0x83,(byte)0x57,(byte)0xbe,(byte)0x4d,(byte)0xbd,(byte)0x77,(byte)0xf0,(byte)0x50,(byte)0x51,(byte)0x5c,0x73,(byte)0xfc,(byte)0xf9,(byte)0xf2};
    //IV 16 bits (préfixe du cipherText)
    byte[] ivBytes = new byte[] {(byte)0x69,(byte)0xdd,(byte)0xa8,(byte)0x45,(byte)0x5c,(byte)0x7d,(byte)0xd4,(byte)0x25,(byte)0x4b,(byte)0xf3,(byte)0x53,(byte)0xb7,(byte)0x73,(byte)0x30,(byte)0x4e,(byte)0xec};

    //Initialisation
    SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");
    IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);

    //Mode
    Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");

    byte[]  cipherText = new byte[] {(byte)0x0e,(byte)0xc,(byte)0x77,(byte)0x02,(byte)0x33,(byte)0x00,(byte)0x98,(byte)0xce,(byte)0x7f,(byte)0x75,(byte)0x20,(byte)0xd1,(byte)0xcb,(byte)0xbb,(byte)0x20,(byte)0xfc,(byte)0x38,(byte)0x8d,(byte)0x1b,(byte)0x0a,(byte)0xdb,(byte)0x50,(byte)0x54,(byte)0xdb,(byte)0xd7,(byte)0x37,(byte)0x08,(byte)0x49,(byte)0xdb,(byte)0xf0,(byte)0xb8,(byte)0x8d,(byte)0x39,(byte)0x3f,(byte)0x25,(byte)0x2e,(byte)0x76,(byte)0x4f,(byte)0x1f,(byte)0x5f,(byte)0x7a,(byte)0xd9,(byte)0x7e,(byte)0xf7,(byte)0x9d,(byte)0x59,(byte)0xce,(byte)0x29,(byte)0xf5,(byte)0xf5,(byte)0x1e,(byte)0xec,(byte)0xa3,(byte)0x2e,(byte)0xab,(byte)0xed,(byte)0xd9,(byte)0xaf,(byte)0xa9,(byte)0x32,(byte)0x29}; 
    cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);  
    byte [] original = cipher.doFinal(cipherText);
    String plaintext = new String(original);
    System.out.println("plaintext: " + plaintext );
}

}

The result is => plaintext: CŸUnfpL¨KH¹)VPÅ|ÉÒ9}FÅgÿ žQ3Š®¹zÛ˜ˆ±<þãh¤ÔÆË“M±§|@+0H5§ So it seems to be wrong

Thank you in advance :)

Answer 1

There could be other problems, but the cipher text in your question, after the 16 first bytes, starts with 0ec770, whereas the cipher text in the Java code starts with

0x0e, 0xc, 0x77

They don't match.