This is an exercise in secure symmetric-key encryption, implemented in purePython (only built-in libraries used), expanded from Bo Zhu's (http://about.bozhu.me)AES-128 implementation at https://github.com/bozhu/AES-Python
encrypt
and decrypt
functions for protecting arbitrary data with apasswordNote: this implementation is not resistant to side channel attacks.
Generation - python generate aes key Encrypt & Decrypt using PyCrypto AES 256 (6) Another take on this (heavily derived from solutions above) but. Aug 10, 2018 This tutorial explains how to encrypt and decrypt text using private and public key encryption, also known as asymmetric encryption. AES cryptography implementation with Python Complete.
Although this is an exercise, the encrypt
and decrypt
functions shouldprovide reasonable security to encrypted messages. It ensures the data iskept secret (using AES), blocks are encrypted together (CBC), the samemessage encrypted twice will have different ciphertexts (salt), the ciphertexthasn't been tampered with (HMAC) and the key has some defense against brute-force(PBKDF2).
The algorithm is as follows:
16 random bytes of salt are extracted from the system's secure random numbergenerator (usually /dev/urandom)>
The given master key is stretched and expanded by PKBDF2-HMAC(SHA256) usingthe salt from 1), to generate the AES key, HMAC key and IV (initializationvector for CBC).
The given message is encrypted with AES-128 using the AES key and IV fromstep 2), in CBC mode and PKCS#7 padding.
A HMAC-SHA256 is generated from the concatenation of the salt from 1) andthe ciphertext from 3).
The final ciphertext is HMAC + salt + ciphertext.
Security overview:
The random salt ensures the same message will map to different ciphertexts.
The HMAC ensures the integrity of both the entire ciphertext and the PKBDF2salt; encrypt-then-mac prevents attacks like Padding Oracle.
Bytes from keys, iv and salt are not reused in different algorithms.
PBKDF2 key stretching allows for relatively weak passwords to be used as AESkeys and be moderately resistant to brute-force, but sacrificing performance.