This repository contains tools for encrypting and decrypting any file using a hybrid encryption method, making use of symmetric AES 256 and asymmetric RSA encryption.

This repository is an extension of the Encryption and Decryption with Python project, portions of the code from this project were used here. The implementations of the other technics were done by the owner of this repository.

This project contains the tools and a skill showcase:

The project works by using two scripts, one for encrypting the file and the other for decrypting it.

The process of encryption starts by loading the data-to-be-encrypted into the program memory. After loading the data into memory, the symmetric and asymmetric keys are generated. For the symmetric encryption, a key is generated as a random 256-bit value and another random 128-bit value is also generated to be used as the initialization vector, necessary for the symmetric encryption.

The AES 256 object is then generated using the previously created key and iv (initialization vector), it uses the CBC mode for the encryption. The padding object is also generated, it uses PKCS7 as the padding method. After generating the keys and objects for the process, the data is first padded and then encrypted.

Concluding the process of encryption, the program will encrypt the AES key and iv and serialize those. First, the program generates the RSA keys. The private key is generated using a public exponent of 65537 and a key size of 2048. The public key is generated as an instance of the previously created private key.

After being generated, the RSA public key is used for encrypting the AES keys (keys is referencing to the AES key and iv). When generating the AES keys, both the key and iv were created as a Python dictionary, which contained the key and iv identifiers, with the same respective names, and the bytes used for the encryption process, as the values associated with those identifiers. Therefore, the process of AES keys encryption doesn't happen by encrypting the bytes used as the key and iv, but it encrypts the Python object which contains those bytes.

The encryption of the object can be seen as follows:

On picture 1, in the left terminal, can be seen the original object and the encrypted one, and the terminal on the right displays the decrypted object, being equal to the original one, and the deserialized encrypted object.

On picture 2, in the left terminal, can be seen the encrypted .json AES keys. The terminal on the right displays the decrypted json object.

The first step for AES keys encryption is to transform the Python object into a byte object. After the conversion, the object is then encrypted using the RSA private key encryption, and the encrypted data is serialized as a json file. The following steps are the serialization of the RSA keys, which are serialized using the PEM encoding, as a traditional OpenSSH format and using the AES-256-CBC as the encryption algorithm for the private key.

The decryption process is much simpler and follows just a few steps. The first step, it's to load encrypted data into the program memory. After this, the next step is to deserialize the RSA private key and load it into program memory. To complete the decryption process, the AES keys need to be deserialized and also loaded into program memory.

The AES keys deserialization starts by loading the encrypted content of the json file into memory. After loaded, the data is decrypted using the RSA private key, and the byte object is turned back into a Python object, which contains the AES key and iv that will be used for decrypting the file.

Finalizing the decryption process, the file's data is decrypted, using the previously deserialized AES keys, and unpadded. After the decryption process, the data is written back into the original encrypted file.

To use the tools, you can either download each file individually or you can clone this repository by executing the following command:

git clone https://github.com/ItaloHugoMDS/Encryption_and_Decryption_Big_Files_with_Python.git

First thing to be done before using the tools, it's to download the necessary libraries. To perform this step, the requirements.txt should be installed using pip3.

Execute the following command to perform the installation:

pip3 install -r requirements.txt

After the library installation, the tools are ready to be used.

The encryption can be done by using the encryption.py file, which will require the python3 command to be executed, following the syntax:

python3 encryption.py [File_To_Be_Encrypted] [RSA_Private_Key_Password] [Encrypted_File_Name] [RSA_Private_Key_Name] [RSA_Public_Key_Name] [AES_Key_File_Name]

The encryption process can also be done by making use of the encryption file, which can be placed within the /bin directory and executed anywhere on the linux terminal. The file follows the syntax:

./encryption [File_To_Be_Encrypted] [RSA_Private_Key_Password] [Encrypted_File_Name] [RSA_Private_Key_Name] [RSA_Public_Key_Name] [AES_Key_File_Name]

Both files make use of the same arguments. The following arguments are required for the encryption process:

• [File_To_Be_Encrypted]: The file that will be encrypted.
• [RSA_Private_Key_Password]: This will be the password for the RSA private key used for decrypting the files.

The next arguments are optional arguments:

• [Encrypted_File_Name]: This will be the output for the encrypted file. If this argument is provided, the original file will be preserved and the encrypted data will be written within a new file. This argument doesn't affect the file extension, a new file will be created with the name provided, but the file extension will be the same as the original file. (By default, the original file will be overwritten with the encrypted data.)
• [RSA_Private_Key_Name]: This argument will change the name of the serialized RSA private key. This argument doesn't affect the file extension, the RSA key will be serialized as a PEM file. (By default, this file will be named Private.pem.)
• [RSA_Public_Key_Name]: This argument will change the name of the serialized RSA public key. This argument doesn't affect the file extension, the RSA key will be serialized as a PEM file. (By default, this file will be named Public.pem.)
• [AES_Key_File_Name]: This argument will change the name of the serialized AES keys, which contain the RSA encrypted AES key and initialization vector. This argument doesn't affect the file extension, the AES key will be saved as a json file. (By default, the file will be named AES_Keys.json.)

The decryption process can be done by using the decryption.py file, which needs the python3 command to be executed. This file requires the following syntax:

python3 decryption.py [File_To_Be_Decrypted] [RSA_Private_Key_Password] [Decrypted_File_Name] [RSA_Private_PEM_File_Name] [AES_Key_File]

This process can also be done by using the decription file, which can also be place inside /bin directory and executed anywhere within the Linux terminal. The syntax for this file is the following:

./decryption [File_To_Be_Decrypted] [RSA_Private_Key_Password] [Decrypted_File_Name] [RSA_Private_PEM_File_Name] [AES_Key_File]

Both decryption files make use of the same arguments. The following are the required ones:

• [File_To_Be_Decrypted]: This will the file to be decrypted.
• [RSA_Private_Key_Password]: This will be the same password used for the encryption process.

The next arguments are optional ones, they are the following:

• [Decrypted_File_Name]: This will be the output for the decrypted file. If this argument is provided, the original encrypted file will be preserved and the decrypted data will be written within a new file. This argument doesn't affect the file extension, a new file will be created with the name provided, but the file extension will be the same as the original encrypted file. (By default, the original file will be overwritten with the encrypted data.)
• [RSA_Private_PEM_File_Name]: This argument only needs to be provided if the default value of the RSA private key file was modified in the encryption process. (By default the program will look for the Private.pem file).
• [AES_Key_File]: This argument only needs to be provided if the default value of the AES Keys file was modified in the encryption process. (By default the program will look for the AES_Keys.json file).

In the skill showcase of the tools, the archive that will be used for encryption and decryption is going to be the Example_of_Data.jpeg, which contains the following content:

This showcase will make use of the encryption and decryption files. However, the commands used here can also be applied to the .py files as well, making use of the proper syntax for the files as demonstrated on the how to use section.

The first step showcases the encryption process of the data. This step will demonstrate the basic use of the tool without the use of the optional arguments, later on the those will also be demonstrated.

1 - Displaying the unencrypted image:

2 - Script's arguments:

3 - Encrypting the image and displaying the encrypted data:

1 - Script's arguments:

2 - Decrypting the image and displaying the decrypted data:

The tools also provide extra arguments which can be used to alter the output file and the other files generated. Here it is how you can use those optional arguments:

1 - Encrypting data using extra arguments:

1 - Decrypting using extra arguments:

This project was only made possible due to the following references:

• Symmetric Encryption: cryptography.io
• Symmetric Encryption Example: elc.github.io
• Symmetric Padding: cryptography.io
• Python Object Serialization: educba.com

To the authors of those articles and websites, my deepest and sincere, thank you. Thank you for providing me with the concepts and knowledge necessary so that I could make my ideas into something real.