Aes Key Generation In Python

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  1. A pure-Python implementation of the AES block cipher algorithm and the common modes of operation (CBC, CFB, CTR, ECB and OFB).
  2. The following steps are involved in generating RSA keys −. Create two large prime numbers namely p and q. The product of these numbers will be called n, where n= p.q. Generate a random number which is relatively prime with (p-1) and (q-1). Let the number be called as e. Calculate the modular inverse of e.

AES (Advanced Encryption Standard) is a symmetric block cipher standardizedby NIST . It has a fixed data block size of 16 bytes.Its keys can be 128, 192, or 256 bits long.

Generation

AES is very fast and secure, and it is the de facto standard for symmetricencryption.

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As an example, encryption can be done as follows:

Random key generation; String encryption; Java version. Openjdk8; oraclejdk9; openjdk9; oraclejdk11; openjdk11; oraclejdk13; openjdk13; Example Code for Java String Encryption with key generation using AES-GCM.

The recipient can obtain the original message using the same keyand the incoming triple (nonce,ciphertext,tag):

Module’s constants for the modes of operation supported with AES:

Python
var MODE_ECB:Electronic Code Book (ECB)
var MODE_CBC:Cipher-Block Chaining (CBC)
var MODE_CFB:Cipher FeedBack (CFB)
var MODE_OFB:Output FeedBack (OFB)
var MODE_CTR:CounTer Mode (CTR)
var MODE_OPENPGP:
OpenPGP Mode
var MODE_CCM:Counter with CBC-MAC (CCM) Mode
var MODE_EAX:EAX Mode
var MODE_GCM:Galois Counter Mode (GCM)
var MODE_SIV:Syntethic Initialization Vector (SIV)
var MODE_OCB:Offset Code Book (OCB)
Crypto.Cipher.AES.new(key, mode, *args, **kwargs)

Create a new AES cipher.

Parameters:
  • key (bytes/bytearray/memoryview) –

    The secret key to use in the symmetric cipher.

    It must be 16, 24 or 32 bytes long (respectively for AES-128,AES-192 or AES-256).

    For MODE_SIV only, it doubles to 32, 48, or 64 bytes.

  • mode (One of the supported MODE_* constants) – The chaining mode to use for encryption or decryption.If in doubt, use MODE_EAX.
Keyword Arguments:

  • iv (bytes, bytearray, memoryview) –(Only applicable for MODE_CBC, MODE_CFB, MODE_OFB,and MODE_OPENPGP modes).

    The initialization vector to use for encryption or decryption.

    For MODE_CBC, MODE_CFB, and MODE_OFB it must be 16 bytes long.

    For MODE_OPENPGP mode only,it must be 16 bytes long for encryptionand 18 bytes for decryption (in the latter case, it isactually the encrypted IV which was prefixed to the ciphertext).

    If not provided, a random byte string is generated (you must thenread its value with the iv attribute).

  • nonce (bytes, bytearray, memoryview) –(Only applicable for MODE_CCM, MODE_EAX, MODE_GCM,MODE_SIV, MODE_OCB, and MODE_CTR).

    A value that must never be reused for any other encryption donewith this key (except possibly for MODE_SIV, see below).

    For MODE_EAX, MODE_GCM and MODE_SIV there are norestrictions on its length (recommended: 16 bytes).

    For MODE_CCM, its length must be in the range [7..13].Bear in mind that with CCM there is a trade-off between noncelength and maximum message size. Recommendation: 11 bytes.

    For MODE_OCB, its length must be in the range [1..15](recommended: 15).

    For MODE_CTR, its length must be in the range [0..15](recommended: 8).

    For MODE_SIV, the nonce is optional, if it is not specified,then no nonce is being used, which renders the encryptiondeterministic.

    If not provided, for modes other than MODE_SIV`, a randombyte string of the recommended length is used (you must thenread its value with the nonce attribute).

  • segment_size (integer) –(Only MODE_CFB).The number of bits the plaintext and ciphertextare segmented in. It must be a multiple of 8.If not specified, it will be assumed to be 8.

  • mac_len : (integer) –(Only MODE_EAX, MODE_GCM, MODE_OCB, MODE_CCM)Length of the authentication tag, in bytes.

    It must be even and in the range [4..16].The recommended value (and the default, if not specified) is 16.

  • msg_len : (integer) –(Only MODE_CCM). Length of the message to (de)cipher.If not specified, encrypt must be called with the entire message.Similarly, decrypt can only be called once.

  • assoc_len : (integer) –(Only MODE_CCM). Length of the associated data.If not specified, all associated data is buffered internally,which may represent a problem for very large messages.

  • initial_value : (integer or bytes/bytearray/memoryview) –(Only MODE_CTR).The initial value for the counter. If not present, the cipher willstart counting from 0. The value is incremented by one for each block.The counter number is encoded in big endian mode.

  • counter : (object) –Instance of Crypto.Util.Counter, which allows full customizationof the counter block. This parameter is incompatible to both nonceand initial_value.

  • use_aesni : (boolean) –Use Intel AES-NI hardware extensions (default: use if available).

Return:

an AES object, of the applicable mode.

  • Getting a Key

Using the cryptography module in Python, this post will look into methods of generating keys, storing keys and using the asymmetric encryption method RSA to encrypt and decrypt messages and files. We will be using cryptography.hazmat.primitives.asymmetric.rsa to generate keys.

Installing cryptography

Since Python does not come with anything that can encrypt files, we will need to use a third-party module.

PyCrypto is quite popular but since it does not offer built wheels, if you don't have Microsoft Visual C++ Build Tools installed, you will be told to install it. Instead of installing extra tools just to build this, I will be using the cryptography module. To install this, execute:

To make sure it installed correctly, open IDLE and execute:

If no errors appeared it has been installed correctly.

What is Asymmetric Encryption?

If you read my article on Encryption and Decryption in Python, you will see that I only used one key to encrypt and decrypt.

Asymmetric encryption uses two keys - a private key and a public key. Public keys are given out for anyone to use, you make them public information. Anyone can encrypt data with your public key and then only those with the private key can decrypt the message. This also works the other way around but it is a convention to keep your private key secret.

Aes Key Generation In Python 8

Getting a Key

To generate the two keys, we can call rsa.generate_private_key with some general parameters. The public key will be found in the object that holds the creation of the private key.

Storing Keys

To store the keys in a file, they first need to be serialized and then written to a file. To store the private key, we need to use the following.

Generation

You can password protect the contents of this file using this top key serialization example.

To store the public key, we need to use a slightly modified version.

Remember that public and private keys are different so you will have to use these methods for each key.

Reading Keys

To get the keys out of the files, we need to read each file and then load them. To read the private key, use the following.

If you store the key with a password, set password to what you used.

The variable private_key will now have the private key. To read the public key, we need to use a slightly modified version.

The variable public_key will now have the public key.

Encrypting

Due to how asymmetric encryption algorithms like RSA work, encrypting with either one is fine, you just will need to use the other to decrypt. Applying a bit of logic to this can create some useful scenarios like signing and verification. For this example, I will assume that you keep both keys safe and don't release them since this example is only for local encryption (can be applied to wider though when keys are exchanged).

This means you can use either key but I will demonstrate using the public key to encrypt, this will mean anyone with the private key can decrypt the message.

Decrypting

Assuming that the public key was used to encrypt, we can use the private key to decrypt.

Demonstration

Aes Key Generation In Python 2

To show this in action, here is a properly constructed example.

Encrypting and Decrypting Files

To encrypt and decrypt files, you will need to use read and write binary when opening files. You can simply substitute the values I previously used for message with the contents of a file. For example:

Using the variable message you can then encrypt it. To store, you can use the general Python method when encryption returns bytes.

Now to decrypt you can easily read the data from test.encrypted like the first bit of code in this section, decrypt it and then write it back out to test.txt using the second bit of code in this section.