python实现SHA256和RSA算法

Python中可以使用内置的`hashlib`库来实现SHA256哈希函数，它是用于生成消息摘要的一种安全散列函数。你可以像下面这样使用：

import hashlib

def sha256_hash(data):
    sha256 = hashlib.sha256()
    sha256.update(data.encode('utf-8'))
    return sha256.hexdigest()

# 示例
data = "Hello, World!"
hashed_data = sha256_hash(data)
print("SHA256 hash:", hashed_data)

对于RSA加密算法，Python并没有直接提供内置支持，但你可以使用第三方库如`cryptography`。首先安装这个库：

pip install cryptography

然后你可以创建密钥对并进行加解密操作：

from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa, padding
from cryptography.hazmat.backends import default_backend

def generate_rsa_keys():
    private_key = rsa.generate_private_key(
        public_exponent=65537,
        key_size=2048,
        backend=default_backend()
    )
    public_key = private_key.public_key()
    return private_key, public_key

def encrypt(message, public_key):
    encrypted = public_key.encrypt(
        message.encode(),
        padding.OAEP(
            mgf=padding.MGF1(algorithm=hashes.SHA256()),
            algorithm=hashes.SHA256(),
            label=None
        )
    )
    return encrypted

def decrypt(encrypted_message, private_key):
    decrypted = private_key.decrypt(
        encrypted_message,
        padding.OAEP(
            mgf=padding.MGF1(algorithm=hashes.SHA256()),
            algorithm=hashes.SHA256(),
            label=None
        )
    )
    return decrypted.decode()

# 示例
private_key, public_key = generate_rsa_keys()
message = "This is a secret message"
encrypted = encrypt(message, public_key)
decrypted = decrypt(encrypted, private_key)
print("Encrypted:", encrypted)
print("Decrypted:", decrypted)