Pycryptodome 中的 RSA 加密/解密是如何完成的

Question

我正在阅读 pycryptodome 的文档，并对如何是数据加密并传输到接收方，然后在那里解密

我所理解的是

在发送方，发送方的公钥用于加密一段数据，然后将其写入.bin 文件

from Crypto.PublicKey import RSA
from Crypto.Random import get_random_bytes
from Crypto.Cipher import AES, PKCS1_OAEP

data = "I met aliens in UFO. Here is the map.".encode("utf-8")
file_out = open("encrypted_data.bin", "wb")

recipient_key = RSA.import_key(open("receiver.pem").read())
session_key = get_random_bytes(16)

# Encrypt the session key with the public RSA key
cipher_rsa = PKCS1_OAEP.new(recipient_key)
enc_session_key = cipher_rsa.encrypt(session_key)

# Encrypt the data with the AES session key
cipher_aes = AES.new(session_key, AES.MODE_EAX)
ciphertext, tag = cipher_aes.encrypt_and_digest(data)
[ file_out.write(x) for x in (enc_session_key, cipher_aes.nonce, tag, ciphertext) ]
file_out.close()

位于接收器（应该接收数据的目的地），.bin 文件使用接收器的私钥加载和解密

from Crypto.PublicKey import RSA
from Crypto.Cipher import AES, PKCS1_OAEP

file_in = open("encrypted_data.bin", "rb")

private_key = RSA.import_key(open("private.pem").read())

enc_session_key, nonce, tag, ciphertext = \
   [ file_in.read(x) for x in (private_key.size_in_bytes(), 16, 16, -1) ]

# Decrypt the session key with the private RSA key
cipher_rsa = PKCS1_OAEP.new(private_key)
session_key = cipher_rsa.decrypt(enc_session_key)

# Decrypt the data with the AES session key
cipher_aes = AES.new(session_key, AES.MODE_EAX, nonce)
data = cipher_aes.decrypt_and_verify(ciphertext, tag)
print(data.decode("utf-8"))

现在，据我了解发送方和接收方之一有两个 .pem 文件，一个是公钥，另一个是私有文件，

我不明白的是：为什么我们有一个 session_key 和数据如何用接收者的私钥解密？