Decryptor/Decryptor/SymmetricEncryptionBox.cpp

#include "Openssl_crypto.h"
class SymmetricEncryptionBox {
  uint8_t iv[12];
  uint8_t symmetric_key[32]; // SHA256 used with ECDHE -> or AES whatever symmetric_key.
  // increments last 4 bytes (in big-endian order)
  uint32_t aes_gcm_increment_iv_internal_call(uint8_t* iv)  {
  	uint32_t counter;
  	for(counter=11;counter>7;counter--)
  	{
  		if(iv[counter] == 0xff)
  		{
  			if(counter - 1 == 7)
  				return 0xff;
  			iv[counter-1] = 0x01;
  			iv[counter] = 0x0;
  		}
  		else
  			iv[counter] += 1;
  	}
  	return 0;
  }

public:
  SymmetricEncryptionBox();
  uint32_t set_symmetric_key(uint8_t* given_key);
  uint32_t encrypt_decrypt(int enc, uint8_t* plaintext, uint32_t plaintext_length, uint8_t* ciphertext, uint32_t* ciphertext_length, uint8_t* tag);

  uint32_t set_symmetric_key(uint8_t* given_key)
  {
    uint32_t counter;
    for(counter=0; counter<32; counter++)
      symmetric_key[counter] = given_key[counter];
  }

  // TODO: IMPORTANT - CHECK IF WE NEED TO DO THIS FOR DECRYPTION TOO.
  uint32_t encrypt_decrypt(int enc, uint8_t* plaintext, uint32_t plaintext_length, uint8_t* ciphertext, uint32_t* ciphertext_length, uint8_t* tag)
  {
    uint32_t return_status = aes_gcm(enc, symmetric_key, iv, plaintext, plaintext_length, ciphertext, ciphertext_length, tag);
    if(return_status == 0)
      aes_gcm_increment_iv_internal_call(iv);
  }
}