refactors project structure

apps/cli/blob.py

@@ -0,0 +1,51 @@
+from binascii import hexlify, unhexlify
+from hashlib import sha256
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+from apps.cli import SUPPORTED_HASH_FUNCTIONS, SUPPORTED_CIPHERS
+
+
+class Blob:
+    def __init__(self, data, cipher, hash_function):
+        self.data = data
+        self.cipher = cipher
+        self.hash_function = hash_function
+
+        # FIXME: We only support SHA256 for now
+        if self.hash_function.upper() not in SUPPORTED_HASH_FUNCTIONS:
+            raise Exception("Hash function not supported ({}). Supported Hash functions: {}"
+                            .format(self.hash_function, SUPPORTED_HASH_FUNCTIONS))
+
+        # FIXME: We only support AES-GCM-128 for now
+        if self.cipher.upper() not in SUPPORTED_CIPHERS:
+            raise Exception("Cipher not supported ({}). Supported ciphers: {}".format(self.hash_function,
+                                                                                      SUPPORTED_CIPHERS))
+
+    def encrypt(self, tx_id, debug, logging):
+        # Transaction to be encrypted
+        # FIXME: The blob data should contain more things that just the transaction. Leaving like this for now.
+        tx = unhexlify(self.data)
+
+        # FIXME: tx_id should not be necessary (can be derived from tx SegWit-like). Passing it for now
+        # Extend the key using HKDF
+        tx_id = unhexlify(tx_id)
+
+        # master_key = H(tx_id | tx_id)
+        master_key = sha256(tx_id + tx_id).digest()
+
+        # The 16 MSB of the master key will serve as the AES GCM 128 secret key. The 16 LSB will serve as the IV.
+        sk = master_key[:16]
+        nonce = master_key[16:]
+
+        # Encrypt the data
+        aesgcm = AESGCM(sk)
+        encrypted_blob = aesgcm.encrypt(nonce=nonce, data=tx, associated_data=None)
+        encrypted_blob = hexlify(encrypted_blob).decode()
+
+        if debug:
+            logging.info("[Client] creating new blob")
+            logging.info("[Client] master key: {}".format(hexlify(master_key).decode()))
+            logging.info("[Client] sk: {}".format(hexlify(sk).decode()))
+            logging.info("[Client] nonce: {}".format(hexlify(nonce).decode()))
+            logging.info("[Client] encrypted_blob: {}".format(encrypted_blob))
+
+        return encrypted_blob