The use of Python encryption library is as follows: 1. Symmetric encryption is recommended to use the Fernet module in the cryptography library. The key is generated by generate_key() and the data is encrypted and decrypted with encrypt()/decrypt(); 2. The hashlib library can be used for hash calculation, and the SHA256 algorithm is preferred and the hash value is obtained through hexdigest(). Be careful to avoid MD5 and SHA1; 3. Asymmetric encryption can use the RSA function of cryptography to generate key pairs through generate_private_key(), and encrypt with public and private keys. Note that filling schemes such as OAEP must be used and are only suitable for encrypting short content. The keys must be kept properly during use to ensure the security of transmission and follow standard encryption practices to improve security.

How to use Python encryption library? Actually, it’s not difficult, but you have to pay attention to a few key points.

Python has several commonly used encryption libraries, such as cryptography , PyCrypto (no longer maintained), hashlib , hmac , etc. Among them, cryptography is currently officially recommended modern encryption library , with comprehensive functions and high security. The following starts with several common usage scenarios and talks about how to use this library to do basic encryption operations.

How to use cryptography to do symmetric encryption?

Symmetric encryption refers to the same key used for encryption and decryption. Common algorithms are AES (Advanced Encryption Standard).

In cryptography , it is recommended to use the Fernet module to achieve simple symmetric encryption. It encapsulates AES-CBC and HMAC, which is simple and safe to use.

The sample code is as follows:

 from cryptography.fernet import Fernet

# Generate key = Fernet.generate_key()
cipher = Fernet(key)

# Encrypt token = cipher.encrypt(b"Secret message!")
print(token) # The output is similar: gAAAAABl...

# Decrypt plain_text = cipher.decrypt(token)
print(plain_text.decode()) # Output: Secret message!

Some points to note:

• The key must be properly saved and cannot be disclosed;
• Fernet uses URL-safe Base64 encoding by default, so there is no problem when transmitting;
• If you want to control the key yourself, you can use base64.urlsafe_b64encode() to construct a key that meets the requirements.

How to use hashlib for hash calculation?

Hash functions are often used to generate data fingerprints or password storage. hashlib in the Python standard library supports a variety of algorithms such as MD5, SHA1, SHA256, etc.

For example, generate a SHA256 hash of a string:

 import hashlib

data = "hello world".encode()
sha256_hash = hashlib.sha256(data).hexdigest()
print(sha256_hash)

Application scenarios include:

• Do not store the user password directly in plain text, but the hash value after adding salt;
• When verifying file integrity, you can compare hash values;
• Note: MD5 and SHA1 have proven unsafe, and it is recommended to use SHA256 or SHA3 first.

How to do asymmetric encryption? RSA Example

Asymmetric encryption uses public key encryption and private key decryption. Commonly used in digital signatures, HTTPS and other scenarios. cryptography supports RSA generation, encryption and signature.

Example of generating an RSA key pair:

 from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

# Generate private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)
public_key = private_key.public_key()

# Serialize private key pem_private = private_key.private_bytes(
    encoding=serialization.Encoding.PEM,
    format=serialization.PrivateFormat.TraditionalOpenSSL,
    encryption_algorithm=serialization.NoEncryption()
)

# Serialize public key pem_public = public_key.public_bytes(
    encoding=serialization.Encoding.PEM,
    format=serialization.PublicFormat.SubjectPublicKeyInfo
)

In practice, please note:

• Private keys must be strictly confidential;
• Before encryption, fill processing (such as OAEP), otherwise it will be easily cracked;
• Asymmetric encryption is not suitable for large files, and usually only short content such as "session keys" are encrypted.

Basically that's it. Encryption seems complicated, but in fact, as long as you choose the right tool and follow the standard process, many problems can be avoided. A library like cryptography that has active maintenance is more reliable to use.

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