sample1.md

1. Block Cipher Mode On A Single-Block

Here is an example of the basic usage of the library.

/*    sample.cpp    */
#include <iostream>
#include "BlockCipherModes/cbc.hpp"

using namespace Mode;

int main()
{
  constexpr size_t BLOCK_LEN = 16;

  unsigned char iv_enc[BLOCK_LEN] = {
    0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe, 0xba, 0xbe,
    0xba, 0xd2, 0xde, 0xed, 0xff, 0x11, 0x22, 0x33,
  };

  unsigned char iv_dec[BLOCK_LEN] = {
    0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe, 0xba, 0xbe,
    0xba, 0xd2, 0xde, 0xed, 0xff, 0x11, 0x22, 0x33,
  };

  unsigned char data[BLOCK_LEN] = {
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
    0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, 0xfa, 0x7e, 
  };

  CBC<BLOCK_LEN>::encrypt(data, iv_enc, [](unsigned char* block) {
    // this is where you will encrypt the `block` and
    // sometime add padding.
    
    // But for this sample we just leave the block "as is", no
    // need to encrypt and decrypt, it will still work, but keep
    // in mind in real applications we should use a block cipher
    // inside this callback method to achieve maximum security.
  });

  CBC<BLOCK_LEN>::decrypt(data, iv_dec, [](unsigned char* block) {
    // this is where you will decrypt the `block`
    // but for this sample we just leave the block "as is"
  });
}

Both the iv_enc, iv_dec are modified after every encrypt, decrypt function call, the data array will also be encrypted, decrypted.

The IV arrays are modified based on the block cipher mode, the modified IV is used for the next encryption or decryption of the remaining blocks if dealing with multi-block data.

Encrypted Value:

// encrypted `data` array.
0xde, 0xac, 0xbc, 0xec, 0xce, 0xfb, 0xbc, 0xb9,
0x10, 0x69, 0x12, 0x30, 0x11, 0xee, 0xd8, 0x4d, 

// decrypted `data` array.
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, 0xfa, 0x7e, 

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Contents

1. Go Back To README
2. Block Cipher Mode On Multi-Block
3. Block Cipher Mode + Block Cipher : Local Access
4. Block Cipher Mode + Block Cipher : Global Access