How to use 'System.Security.Cryptography.AesManaged' to encrypt a byte[] ?

Question

Hi,

Basically i want to use System.Security.Cryptography.AesManaged (or a better class, if you think there is one?) to take one byte array and create another encrypted byte array, using a given symmetric key (i assume i'll need one?).

I also will need the way to reverse this procedure.

The point of this is so i can encrypt stored passwords. I assume there's a simple way to do this?

Thanks

Answer 1

Simple encrypting and decrypting data in C#.

Edit: For passwords, I would recommend using SHA-2 hash instead of doing a two-way encryption, unless you really need to recover the original password. Normally you just need the fact that someone knew the password, not the password itself.

Answer 2

EDIT: Noticed eed3si9n's edit... I agree, symmetric encryption is a bad choice for passwords. Use hashes (and not MD5) instead. Here's a very complete example.

A simple example:

byte[] clear = GetCleartext();
HashAlgorithm sha2 = SHA256CryptoServiceProvider.Create();
byte[] hashed = sha2.ComputeHash(clear);

To validate a correct password, you would run the same computation over the provided password, and compare the result to the hash you have in your database.

It's good practice to add salt (random data) to the cleartext to avoid rainbow table attacks. Basically, append a known randomly-generated value, unique to that user, to the cleartext before hashing.

Answer 3

Here's what i did in the end, inspired by (an older version of) michael's answer:

private string Encrypt(string input)
{
  return Convert.ToBase64String(Encrypt(Encoding.UTF8.GetBytes(input)));
}
private byte[] Encrypt(byte[] input)
{
  PasswordDeriveBytes pdb = new PasswordDeriveBytes("hjiweykaksd", new byte[] { 0x43, 0x87, 0x23, 0x72, 0x45, 0x56, 0x68, 0x14, 0x62, 0x84 });
  MemoryStream ms = new MemoryStream();
  Aes aes = new AesManaged();
  aes.Key = pdb.GetBytes(aes.KeySize / 8);
  aes.IV = pdb.GetBytes(aes.BlockSize / 8);
  CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write);
  cs.Write(input, 0, input.Length);
  cs.Close();
  return ms.ToArray();
}
private string Decrypt(string input)
{
  return Encoding.UTF8.GetString(Decrypt(Convert.FromBase64String(input)));
}
private byte[] Decrypt(byte[] input)
{
  PasswordDeriveBytes pdb = new PasswordDeriveBytes("hjiweykaksd", new byte[] { 0x43, 0x87, 0x23, 0x72, 0x45, 0x56, 0x68, 0x14, 0x62, 0x84 });
  MemoryStream ms = new MemoryStream();
  Aes aes = new AesManaged();
  aes.Key = pdb.GetBytes(aes.KeySize / 8);
  aes.IV = pdb.GetBytes(aes.BlockSize / 8);
  CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write);
  cs.Write(input, 0, input.Length);
  cs.Close();
  return ms.ToArray();
}