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I'm almost new to encryption. I am trying to decrypt an array of bytes, and when I am providing the IV I am getting an exception : InvalidAlgorithmParameterException (no iv set when one expected). Here's my code ( iv is an array of 16 bytes which is not null and has the values used when encrypting) : Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.DECRYPT_MODE, encriptionKey,new IvParameterSpec(iv)); If I don't specify the IV the cipher gets initialized ok : Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); cipher.init(Cipher.DECRYPT_MODE, encriptionKey); Trying to find an answer I did find an implementation of JCEStreamCipher ( here ) which may not correspond to the version I am using but has some code that makes me thing I am not understanding it correctly. Here's the code : if ((ivLength != 0) && !(param instanceof ParametersWithIV)) { SecureRandom ivRandom = random; if (ivRandom == null) { ivRandom = new SecureRandom(); } if ((opmode == Cipher.ENCRYPT_MODE) || (opmode == Cipher.WRAP_MODE)) { byte[] iv = new byte[ivLength]; ivRandom.nextBytes(iv); param = new ParametersWithIV(param, iv); ivParam = (ParametersWithIV)param; } else { throw new InvalidAlgorithmParameterException("no IV set when one expected"); } } Looks like I cannot provide an IV when decrypting, but it doesn't makes too much sense to me. any help will be greatly appreciated. thanks a lot, richard.

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