python实现X3DH算法

X3DH算法是一种密钥交换协议，它可以在两个通信方之间安全地交换密钥。下面是Python实现X3DH算法的步骤：

1. 导入所需的库

from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
from cryptography.hazmat.primitives.kdf.hkdf import HKDF
from cryptography.hazmat.primitives import hashes

2. 生成身份验证密钥

identity_key = X25519PrivateKey.generate()

3. 生成预共享密钥

prekey = X25519PrivateKey.generate()
prekey_public = prekey.public_key()

4. 生成ECDH密钥对

ephemeral_key = X25519PrivateKey.generate()
ephemeral_public = ephemeral_key.public_key()

5. 计算DH密钥

dh1 = prekey.exchange(ephemeral_public)
dh2 = identity_key.exchange(prekey_public)
dh3 = identity_key.exchange(ephemeral_public)

6. 计算HKDF密钥

secret = dh1 + dh2 + dh3
derived_key = HKDF(
    algorithm=hashes.SHA256(),
    length=32,
    salt=None,
    info=b'',
).derive(secret)

7. 使用HKDF密钥加密消息

from cryptography.fernet import Fernet

cipher_suite = Fernet(derived_key)
cipher_text = cipher_suite.encrypt(b"Hello, world!")

8. 解密消息

plain_text = cipher_suite.decrypt(cipher_text)