CODEWITHSUNDEEP
javaencryption
user966682
user966682

Reputation: 111

How to decrypt pbkdf2 encrypted text without knowing the IV

I am trying to decrypt an encrypted text. I have the salt value, iteration count and key length. But i don't have the initialization vector (IV) value, how can i go about and decrypt this. I also have secret key.

For time being I am using some random IV value whose size is 16 bytes. But still i am not able to decrypt the value properly. Can anyone please help as i am stuck with this for a long time?

Below are the values which were given to me.

salt= EW0h0yUcDX72WU9UiKiCwDpXsJg=, Iteration=128,Keylenght=16.
MasterKeyName="Passphrase1", MACMethod algo = hmac-sha1,    MACKey="jq/NdikC7AZf0Z+HEL5NrCICV8XW+ttzl/8687hVGHceoyJAaFws+111plQH 6Mlg" encrypted kae =   "pM7VB/KomPjq2cKaxPr5cKT1tUZN5tGMI+u1XKJTG1la+ThraPpLKlL2plKk6vQE"   and valuemac="lbu+9OcLArnj6mS7KYOKDa4zRU0=".
Secret key = "xxxxxxxxxxx".

Below is the code which I am using to decrypt.

SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec spec = new PBEKeySpec(secretkey.toCharArray(), salt, iterationCount, keyStrength);    
SecretKey tmp = factory.generateSecret(spec);
key = new SecretKeySpec(tmp.getEncoded(), "AES");
dcipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
AlgorithmParameters params = dcipher.getParameters();
iv = "0000000000000000".getBytes();
System.out.println("IV " + new sun.misc.BASE64Encoder().encodeBuffer(iv));
dcipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));      
byte[] decryptedData = new sun.misc.BASE64Decoder().decodeBuffer(base64EncryptedData);
byte[] utf8 = dcipher.doFinal(decryptedData);

Upvotes: 1

Views: 5262

Answers (1)

Maarten Bodewes
Maarten Bodewes

Reputation: 93948

You cannot decrypt the first block of CBC encrypted ciphertext if you don't know the IV.

It is however not unlikely that you can retrieve the IV value:

  • often the IV value is 16 bytes retrieved after the key bytes) generated from the PBKDF;
  • the IV is often prepended to the ciphertext, resulting in one block of garbage before the full plaintext during decryption;
  • not secure but the IV is also left out or set to a constant value, with an all-zero IV being the most common (this is identical in CBC mode to not using any IV.)

Upvotes: 1

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