Impl the basic signal functions that were listed

messenger.py

@@ -1,6 +1,7 @@
 import os
 import pickle
 import string
+import hmac
 from cryptography.hazmat.primitives import hashes, serialization
 from cryptography.hazmat.primitives.asymmetric import ec
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM
@@ -8,12 +9,51 @@ from cryptography.hazmat.primitives.kdf.hkdf import HKDF
 
 CURVE = ec.SECP256R1()
 
+class MessageHeader:
+    dh: object
+    pn: int
+    n: int
+
 def GENERATE_DH():
     return ec.generate_private_key(CURVE)
 
 def DH(dh_pair, dh_pub):
     return dh_pair.exchange(ec.ECDH(), dh_pub)
 
+def KDF_RK(rk, dh_out):
+    output = HKDF(
+        algorithm=hashes.SHA256(),
+        length=64,
+        salt=rk,
+        info=b"",
+    ).derive(dh_out)
+    return output[:32], output[32:]
+
+
+def KDF_CK(ck):
+    return (
+        hmac.new(ck, b"\x01", "sha256").digest(),
+        hmac.new(ck, b"\x02", "sha256").digest(),
+    )
+
+def ENCRYPT(mk, plaintext, associated_data):
+    nonce = os.urandom(12)
+    return nonce + AESGCM(mk).encrypt(nonce, plaintext, associated_data)
+
+
+def DECRYPT(mk, ciphertext, associated_data):
+    return AESGCM(mk).decrypt(ciphertext[:12], ciphertext[12:], associated_data)
+
+def HEADER(dh_pair, pn, n):
+    public_key = dh_pair.public_key()
+    return MessageHeader(public_key, int(pn), int(n))
+
+def CONCAT(ad, header):
+    header_tup = pickle.dumps(
+        (header.dh.public_bytes(serialization.Encoding.X962,serialization.PublicFormat.UncompressedPoint), header.pn, header.n),
+    )
+    return len(ad).to_bytes(8) + ad + header_tup
+
 class MessengerServer:
     def __init__(self, server_signing_key, server_decryption_key):
         self.server_signing_key = server_signing_key