How to Decrypt OpenSSL AES-CBC Encrypted Files in Java?

Decrypting Files in Java Encrypted with OpenSSL's AES in CBC Mode

OpenSSL encrypts files using a salt-based password key derivation method and base64 MIME encoding. To decrypt such files in Java, adhere to the following steps:

1. Generate Salt and Key:

   salt = random(8)
   keyAndIV = EVP_BytesToKey(password, salt, 48)
   key = keyAndIV[0..31]
   iv = keyAndIV[32..47]

2. Extract Salt and Ciphertext:

   From the base64 encoded file:

   • Salt: bytes 8-15
   • Ciphertext: bytes 16 onwards

3. Decrypt:

   aesCBC.init(Cipher.DECRYPT_MODE, key, iv)
   plaintext = aesCBC.doFinal(ciphertext)

4. OpenSSL EVP_BytesToKey Implementation:

   public static byte[][] EVP_BytesToKey(int key_len, int iv_len, MessageDigest md,
           byte[] salt, byte[] data, int count) {
       // ...
   }

5. Main Decryption Method:

   public static void main(String[] args) {
       // ...
   }

Additional Notes:

• Use ASCII as the character set consistently.
• Specify the digest algorithm (MD5 or SHA-256) in both OpenSSL and Java.
• Use PBKDF2 for improved security.
• Be aware of changes in OpenSSL's digest algorithm between versions.

The above is the detailed content of How to Decrypt OpenSSL AES-CBC Encrypted Files in Java?. For more information, please follow other related articles on the PHP Chinese website!