What cipher mode/padding defaults or common uses of AES encryption would be used with .NET?

Question

I\'m helping someone that needs to send an encrypted value with AES to a customer. The customer has not specified the block cipher mode, padding or how to generate the key. They

Answer 1

There's no constructor for or method in any of the Aes classes in .net that takes in a string as a key. Keys are specified as an array of bytes, such that the length of the array is equal to the key size / 8.

One would hope that they would use a common hash algorithm to generate the key from the 19 character string. Best bet would probably be a Sha256 hash of the string.

Just to give you an idea of what that would look like in .net ...

public void InitializeCrypto()
      {
           var utf8 = new UTF8Encoding();
           var hash = new SHA256CryptoServiceProvider();
           var aes = new AesCryptoServiceProvider();
           var iv = new byte[16];

           Array.Clear(iv, 0, iv.Length);
           string key = "Some19CharacterString";
           var utf8Bytes = utf8.GetBytes(key);
           aes.IV = iv;
           aes.KeySize = 256;
           aes.Key = hash.ComputeHash(utf8Bytes);
           //Do crypto work

      }