“Padding is invalid and cannot be removed” using AesManaged

Question

I\'m trying to get simple encryption/decryption working with AesManaged, but I keep getting an exception when trying to close the decryption stream. The string here gets en

Answer 1

As others have mentioned, this error can occur if the key/iv is not correctly initialized for decryption. In my case I need to copy key and iv from some larger buffer. Here's what I did wrong:

Does not work: (Padding is invalid and cannot be removed)

aes.Key = new byte[keySize];
Buffer.BlockCopy(someBuffer, keyOffset, aes.Key, 0, keySize);

aes.IV = new byte[ivSize];
Buffer.BlockCopy(someBuffer, ivOffset, aes.IV, 0, ivSize);

Works:

var key = new byte[keySize];
Buffer.BlockCopy(someBuffer, keyOffset, key, 0, keySize);
aes.Key = key;

var iv = new byte[ivSize];
Buffer.BlockCopy(someBuffer, ivOffset, iv, 0, ivSize);
aes.IV = iv;

The OP did not make this mistake, but this might be helpful for others seeing the same error.