AesCipher Class

This class uses the BinaryWriter to generate the encrypted output and BinaryReader to read it.

The data is formatted with an unencrypted header that specifies the initialization vector (IV), as well as the HMAC512 that will be used to validate the encrypted data. The encrypted data includes variable length psuedo random padding followed by the encrypted user data.

 Header (plaintext)
+------------------+
|    0x3BBAA035    |    32-bit magic number (for verification)
+------------------+
|     IV Size      |    16-bits
+------------------+
|                  |
|     IV Bytes     |    IV Size bytes
|                  |
+------------------+
|    HMAC Size     |    16-bits
+------------------+
|                  |
|    HMAC Bytes    |    HMAC Size bytes
|                  |
+-------------------

  AES256 Encrypted:
+------------------+
|   Padding Size   |    16-bits
+------------------+
|                  |
|   Padding Bytes  |    Padding Size bytes
|                  |
+------------------+
|                  |
|                  |
|                  |
|    User Data     |
|                  |
|                  |
|                  |
+------------------+

Note
Note that this encodes multi-byte integers using little endian byte ordering via BinaryWriter and BinaryReader.

This class automatically generates a new initialization vector for every encyption operation. This ensures that every encryption operation will generate different ciphertext even when the key and data haven't changed to enhance security.

The class is designed to be easier to use than the .NET Core AesManaged base implementation.

To encrypt data:

1. Generate an encryption key via GenerateKey(Int32) and create an instance via AesCipher(String, Int32) passing the key, or just call AesCipher(Int32, Int32) to create with a generated key of the specified size.
2. You can always obtain the key via the Key property.
3. Call one of EncryptToBase64(Byte), EncryptToBase64(Byte), EncryptToBytes(String), or EncryptToBytes(Byte) to perform the encryption with varying input and output formats.

To decrypt data:

1. Use AesCipher(String, Int32) to construct and instance using the key originally used to encrypt the data.
2. Call one of DecryptBytesFrom(Byte), DecryptBytesFrom(String), DecryptStringFrom(Byte), or DecryptStringFrom(Byte). to decrypt data.

Reference