RE: Rijndael decryption succeeds SOMETIMES

• Previous message: Nicole Calinoiu: "Re: Appl. Security Problems"
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Date: Tue, 24 May 2005 13:14:11 -0700

I'm not sure if you are having these problems, but I have solved a similar
problem that has been troubling me all afternoon....

1. Check the IV is the same in the decrypt as encrypt (I am sure you already
know this).

2. If you are converting bytes to text using an ASCIIEncoder, or any other
8-bit encoder, it will only convert using 8-bits, i.e. a byte value of 129
will become 1!!

I had this problem because the MSDN sample uses an ASCII encoder! How
annoying!!!!! I hope this helps.

"Derek Knudsen" wrote:

> I'm working on a solution that takes a random passphrase of a user and hashes
> it to produce an crypto key, which is then used to encrypt and decrypt. What
> we are finding is that it works on most machines all the time (throws "PKCS7
> padding is invalid ..." when invalid passphrase passed - probably not a
> perfect check) but not on all of the machines and not all the time.
> Sometimes you can give it a passphrase and the decryption of the encrypted
> information will work. Also, in this case, the decrypted info will be
> different than what it should be. What am I doing wrong? Why is it
> sometimes working on invalid passphrases? Here's the code:
>
> public static byte[] Decrypt(byte[] cipherText_, byte[] salt_, byte[] iv_,
> string passPhrase_)
> {
> byte[] plainText = new byte[cipherText_.Length];
> byte[] temp;
>
> using(MemoryStream cipherStream = new MemoryStream(cipherText_))
> {
> //hash password
> PasswordDeriveBytes key = new PasswordDeriveBytes(passPhrase_, salt_,
> PasswordDeriveHashName, PasswordDeriveIterations);
>
> //Encrypt
> SymmetricAlgorithm sa = RijndaelManaged.Create();
> ICryptoTransform decryptor = sa.CreateDecryptor(key.GetBytes(32), iv_);
> CryptoStream cryptoStream = new CryptoStream(cipherStream, decryptor,
> CryptoStreamMode.Read);
> int read = cryptoStream.Read(plainText, 0, plainText.Length);
> temp = new byte[read];
> Array.Copy(plainText, 0, temp, 0, read);
> }
> return temp;
> }
>
>
>

• Previous message: Nicole Calinoiu: "Re: Appl. Security Problems"
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