AES Manual

Table of Contents

• About
• Create
• Use
• Encryption / Decryption
• Further Reading

About

An Advanced Encryption Standard (AES, also known as Rijndael) class to encrypt/decrypt data.

Warning

For encryption using the MAXON API see Stream Conversions Manual.

  // This example demonstrates the encryption and decryption of a string.
 
  // Some plain text to encrypt.
  const Char  plainText[] = "O brave new world / That has such people in't!";
  const Int32 length = sizeof(plainText);
 
  ApplicationOutput("Plain Text: @", maxon::String { plainText });
 
  // Declare secret key and encryption block size.
  const Int32 blockSize = 256;                                                                              // in bits (either 128, 192 or 256)
  const Char  key[32] = { '7', 'c', '3', '0', 'e', '0', '0', 'b', 'b', '6', '2', '7', '1', '4', '9', '5' }; // either 16, 24 or 32 bytes
  const Int32 keyLength = sizeof(key) * 8;                                                                  // in bits (either 128, 192 or 256)
  DebugAssert((keyLength == 128) || (keyLength == 192) || (keyLength == 256));
 
  // Memory to store the encrypted data.
  void* buffer = nullptr;
  Int   encryptedSize = 0;
 
  // Encrypt data.
  {
    // Get size of the memory needed to store the encrypted data.
    encryptedSize = AES::CalcEncryptedDataSize(blockSize, length);
    DebugAssert(encryptedSize >= length); // Note: encrytedSize is always equal or larger than unencrypted size.
 
    // Allocate needed memory.
    buffer = NewMem(char, encryptedSize) iferr_return;  // No need to clear memory here, will be filled with random data next.
 
    // Fill buffer with random content for increased security (the buffer part behind plainText is also input to the encryption).
    maxon::Block<UChar>         memBlock((UChar*)buffer, encryptedSize);
    maxon::SecureRandomProvider srp = maxon::SecureRandom::GetDefaultProvider();
    if (!maxon::SecureRandom::GetRandomNumber(srp, memBlock))
      return maxon::UnexpectedError(MAXON_SOURCE_LOCATION);
 
    // Copy the given text into the memory.
    CopyMem(plainText, buffer, length);
 
    AutoAlloc<AES> aes;
    if (aes && aes->Init(blockSize, keyLength))
    {
      aes->Encrypt(buffer, encryptedSize, key);
    }
  }
 
  // Decrypt data again.
  {
    AutoAlloc<AES> aes;
    if (buffer && aes && aes->Init(blockSize, keyLength))
    {
      if (aes->Decrypt(buffer, encryptedSize, key))
      {
        const maxon::String text { (char*)buffer };
        ApplicationOutput("Plain Text: @", text);
      }
    }
  }
 
  DeleteMem(buffer);

Create

AES objects are created with the usual tools, see Entity Creation and Destruction Manual (Classic).

• AES::Alloc(): Allocates an AES instance.
• AES::Free(): Destroys an AES instance.

Use

• AES::Init(): Initializes the AES cipher to the given block length and key length.
• AES::CalcEncryptedDataSize(): Calculates the size of the data block (data size + encryption overhead).

  Note

  The encrypted data size is always equal or larger than the unencrypted data size.

Encryption / Decryption

• AES::Encrypt(): Encrypts a data block.
• AES::Decrypt(): Decrypts a data block.

  Note

  Use a buffer of encrypted data size for both operations.

  Warning

  It is recommended to fill the end of the buffer (encrypted size >= data size, so the part after the data to encrypt) with random values (e.g. via maxon::SecureRandom) to increase security.

Further Reading

• Algorithms
• Stream Conversions Manual
• AESFile Manual
• GeCipher256 Manual