在 Java 中解码 C# 生成的 AES IV 和 KEY

Question

In C# they are generating key by using below code.

using System;
using System.Text;
using System.Security.Cryptography;
                    
public class Program
{
    public static void Main()
    {            
                var aesEncryption = new RijndaelManaged
{
    KeySize = 128,
    BlockSize = 128,
    Mode = CipherMode.CBC,
    Padding = PaddingMode.PKCS7

};
    aesEncryption.GenerateIV();
    string ivStr = Convert.ToBase64String(aesEncryption.IV);
    aesEncryption.GenerateKey();
    string keyStr = Convert.ToBase64String(aesEncryption.Key);
    string completeKey = Convert.ToBase64String(ASCIIEncoding.UTF8.GetBytes(ivStr + "," + keyStr));
    // Console.WriteLine(completeKey);
                }
}

Sample completeKey: SENTUkR2QjZ1ZjBYV0o2aXNCcnRqQT09LDJpdTZHMUpWYm0rbTQ2Njl6ZG83Z2c9PQ==

In Java how I decode completeKey to get IV and Key.I used below code and that Key and IV is not 128 Bit and my encryption is failing.

import java.util.Base64;

public class HelloWorld{

     public static void main(String []args){
        String originalInput = "SENTUkR2QjZ1ZjBYV0o2aXNCcnRqQT09LDJpdTZHMUpWYm0rbTQ2Njl6ZG83Z2c9PQ==";

String decodedString = new String(Base64.getDecoder().decode(originalInput.getBytes()));
        String[] arrOfStr = decodedString.split(",", 2); 
        String iv=arrOfStr[0];
        String key=arrOfStr[1];
        System.out.println(decodedString);//HCSRDvB6uf0XWJ6isBrtjA==,2iu6G1JVbm+m4669zdo7gg==
        System.out.println(iv);//HCSRDvB6uf0XWJ6isBrtjA==
        System.out.println(key);//2iu6G1JVbm+m4669zdo7gg==
 

        
       
     }
}

Answer 1

Your IV and key are first encoded to Base64-Strings, then concatenated with a ',' as delimiter, the resulting string is converted to a byte array and then finally Base64-encoded.

The following program is doing it backwards and in the end you find an IV with (correct) length of 16 bytes and an AES key with a length of 16 bytes = 128 bit - both will work for AES encryption in CBC mode.

Security warning: This way of transporting the key will be unsecure in most ways, so the following code is for educational purposes only.

result:

Decode C# generated AES IV and KEY in Java
ivStr: k7ivGm6OoMHRlnk4tZCAMA==
ivExp: k7ivGm6OoMHRlnk4tZCAMA==
keyStr: Lq5wkaGWFknsEKUxoAY46w==
keyExp: Lq5wkaGWFknsEKUxoAY46w==
iv  length: 16 data: 93b8af1a6e8ea0c1d1967938b5908030
key length: 16 data: 2eae7091a1961649ec10a531a00638eb

code:

import java.util.Base64;

public class Main {
    public static void main(String[] args) {
        System.out.println("Decode C# generated AES IV and KEY in Java");
        // https://stackoverflow.com/questions/63503753/decode-c-sharp-generated-aes-iv-and-key-in-java
        /* dataset
        iv:k7ivGm6OoMHRlnk4tZCAMA==
        key: Lq5wkaGWFknsEKUxoAY46w==
        azdpdkdtNk9vTUhSbG5rNHRaQ0FNQT09LExxNXdrYUdXRmtuc0VLVXhvQVk0Nnc9PQ==
         */
        String originalInput = "azdpdkdtNk9vTUhSbG5rNHRaQ0FNQT09LExxNXdrYUdXRmtuc0VLVXhvQVk0Nnc9PQ==";
        byte[] originalInputByte = Base64.getDecoder().decode(originalInput);
        String decodedString = new String(originalInputByte);
        String[] arrOfStr = decodedString.split(",", 2);
        String ivStr = arrOfStr[0];
        String keyStr = arrOfStr[1];
        System.out.println("ivStr: " + ivStr);
        System.out.println("ivExp: " + "k7ivGm6OoMHRlnk4tZCAMA==");
        System.out.println("keyStr: " + keyStr);
        System.out.println("keyExp: " + "Lq5wkaGWFknsEKUxoAY46w==");
        // final conversion to byte[]
        byte[] iv = Base64.getDecoder().decode(ivStr);
        byte[] key = Base64.getDecoder().decode(keyStr);
        System.out.println("iv  length: " + iv.length + " data: " + bytesToHex(iv));
        System.out.println("key length: " + key.length + " data: " + bytesToHex(key));
    }
    private static String bytesToHex(byte[] bytes) {
        StringBuffer result = new StringBuffer();
        for (byte b : bytes) result.append(Integer.toString((b & 0xff) + 0x100, 16).substring(1));
        return result.toString();
    }
}