Is it possible NOT to use IV when implementing Rijndael decryption?

Question

I am using decryption of ciphertext using the Rijndael algorithm. Unfortunately, I do not have access to data encryption and they were provided with only a password (for generating key c) and the type of algorithm.

I don’t have salt (everything seems to be in order) and I don’t have IV. Now, my question is: should I have IV to perform decryption? I suspect that the developers who wrote the encryption did not use salt, or IV (if possible).

I tried to set the value of IV to zero, with no luck, and instantiating Rijndael creates a default value of IV, and this distorts the first 16 characters of my plaintext after decryption.

Is there any way to deny the influence of IV? Or do you need to try and understand that IV is used in encryption?

Answer 1

If the cipher was used for encryption in CBC mode (which is the default ), then you should know IV, there is no way around it.

However, since the purpose of IV is not the same as the password, sometimes you find that IV is added to the encrypted data (so that the recipient can easily capture it for use in decryption).

Answer 2

You can use ECB mode and it will ignore IV. However, you need IV for other modes, such as CBC.

Answer 3

If it was encrypted using IV, then yes, for proper decryption you will need IV.

From your description of the first 16 characters, it looks like you are working in CBC mode. See the chart here, why you will need IV: http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Cipher-block_chaining_.28CBC.29 .