Prototype working

encrypt.py

@@ -1,73 +1,19 @@
 #!/usr/bin/env python3
 
-import secrets
-from Cryptodome.Cipher import AES
-import base64
-import struct
-import subprocess
-import binascii
+import os
 
-def encrypt_file(filename_in, chunk_size=1000000//16):
-    file_id = secrets.token_urlsafe(22)
-    auth_secret = secrets.token_bytes(16)
-    key = secrets.token_bytes(16)
-    data_nonce = secrets.token_bytes(8)
-
-    token_cipher = AES.new(auth_secret, AES.MODE_GCM)
-    ciphertext, token_tag = token_cipher.encrypt_and_digest(key)
-    token = base64.b64encode(ciphertext)
-
-    with open(f'{file_id}.enc', 'wb') as fout, open(filename_in, 'rb') as fin:
-        fout.write(token_cipher.nonce) # 16 bytes
-        fout.write(token_tag) # 16 bytes
-        fout.write(auth_secret) # 16 bytes
-        fout.write(data_nonce) # 8 bytes
-
-        cipher = AES.new(key, AES.MODE_CTR,
-                initial_value=struct.pack('<Q', 0), nonce=data_nonce)
-
-        block = fin.read(cipher.block_size*chunk_size)
-        while block:
-            data = cipher.encrypt(block)
-            fout.write(data)
-            block = fin.read(cipher.block_size*chunk_size)
-
-    return file_id, token
-
-def decrypt_generator(file_id, token, seek=0, chunk_size=1000000//16):
-    with open(f'{file_id}.enc', 'rb') as fin:
-        token_nonce = fin.read(16)
-        token_tag = fin.read(16)
-        auth_secret = fin.read(16)
-        data_nonce = fin.read(8)
-
-        ciphertext = base64.b64decode(token)
-        token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce)
-        key = token_cipher.decrypt_and_verify(ciphertext, token_tag)
-
-        # Use token cipher's block size assuming the two are the same
-        cipher = AES.new(key, AES.MODE_CTR,
-                initial_value=struct.pack('<Q', seek // token_cipher.block_size), nonce=data_nonce)
-        fin.seek(seek - seek % cipher.block_size, 1)
-        offset = seek % cipher.block_size
-
-        block = fin.read(cipher.block_size*chunk_size)
-        while block:
-            data = cipher.decrypt(block)
-            yield data[offset:]
-            offset = 0
-            block = fin.read(cipher.block_size*chunk_size)
+from filecrypt import encrypt_file
 
 if __name__ == '__main__':
     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument('infile')
-    parser.add_argument('outfile')
     args = parser.parse_args()
 
-    file_id, token = encrypt_file(args.infile)
-    
-    with open(args.outfile, 'wb', buffering=8192) as fout:
-        for data in decrypt_generator(file_id, token):
-            fout.write(data)
+    if not os.path.isfile(args.infile):
+        print(f'{infile} is not a file or directory, exiting.')
+        os.exit(2)
 
+    file_id, token = encrypt_file(args.infile)
+    print(f'/{file_id}/{token}/{os.path.basename(args.infile)}')
+    

filecrypt.py

@@ -0,0 +1,71 @@
+import secrets
+from Cryptodome.Cipher import AES
+import base64
+import struct
+import subprocess
+import binascii
+import os
+
+FILE_ID_LENGTH = 22
+TOKEN_LENGTH = 22
+
+def encrypt_file(filename_in, chunk_size=1000000//16):
+    file_id = secrets.token_urlsafe(16)
+    auth_secret = secrets.token_bytes(16)
+    key = secrets.token_bytes(16)
+    data_nonce = secrets.token_bytes(8)
+
+    token_cipher = AES.new(auth_secret, AES.MODE_GCM)
+    ciphertext, token_tag = token_cipher.encrypt_and_digest(key)
+    token = base64.b64encode(ciphertext).rstrip(b'=').decode()
+
+    with open(f'{file_id}.enc', 'wb') as fout, open(filename_in, 'rb') as fin:
+        fout.write(token_cipher.nonce) # 16 bytes
+        fout.write(token_tag) # 16 bytes
+        fout.write(auth_secret) # 16 bytes
+        fout.write(data_nonce) # 8 bytes
+
+        cipher = AES.new(key, AES.MODE_CTR,
+                initial_value=struct.pack('<Q', 0), nonce=data_nonce)
+
+        block = fin.read(cipher.block_size*chunk_size)
+        while block:
+            data = cipher.encrypt(block)
+            fout.write(data)
+            block = fin.read(cipher.block_size*chunk_size)
+
+    return file_id, token
+
+def payload_size(path):
+    return os.stat(path).st_size - 56
+
+def decrypt_generator(filename, token, seek=0, end=None, chunk_size=1000000//16):
+    with open(filename, 'rb') as fin:
+        token_nonce = fin.read(16)
+        token_tag = fin.read(16)
+        auth_secret = fin.read(16)
+        data_nonce = fin.read(8)
+
+        ciphertext = base64.b64decode(token + '='*((3-len(token)%3)%3))
+        token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce)
+        key = token_cipher.decrypt_and_verify(ciphertext, token_tag)
+
+        # Use token cipher's block size assuming the two are the same
+        cipher = AES.new(key, AES.MODE_CTR,
+                initial_value=struct.pack('>Q', seek // token_cipher.block_size), nonce=data_nonce)
+        print('Seeking to position', seek, 'iv', seek // token_cipher.block_size, 'pos', seek - seek %
+                cipher.block_size, 'offset', seek % cipher.block_size)
+        fin.seek(seek - seek % cipher.block_size, 1)
+        offset = seek % cipher.block_size
+
+        to_send = end - seek + 1 if end else None
+        block = fin.read(cipher.block_size*chunk_size)
+        while block and (to_send is None or to_send > 0):
+            data = cipher.decrypt(block)
+            out = data[offset:to_send]
+            yield out
+            if to_send is not None:
+                to_send -= len(out)
+            offset = 0
+            block = fin.read(cipher.block_size*chunk_size)
+

server.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+
+import re
+import os
+
+from flask import Flask, abort, request, Response
+
+import filecrypt
+
+app = Flask(__name__)
+BASE64_RE = re.compile('^[A-Za-z0-9+-_]+=*$')
+
+@app.route('/<file_id>/<token>/<filename>')
+def download(file_id, token, filename):
+    if not BASE64_RE.match(file_id) or len(file_id) != filecrypt.FILE_ID_LENGTH:
+        abort(400, 'Invalid file ID format')
+    if not BASE64_RE.match(token) or len(token) != filecrypt.TOKEN_LENGTH:
+        abort(400, 'Invalid token format')
+
+    path = f'{file_id}.enc'
+    size = filecrypt.payload_size(path)
+
+    range_header = re.match('^bytes=([0-9]+)-([0-9]*)$', request.headers.get('Range', ''))
+    if not range_header:
+        response = Response(
+                filecrypt.decrypt_generator(path, token),
+                mimetype='application/octet-stream')
+        response.headers['Content-Length'] = size
+    else:
+        range_start, range_end = range_header.groups()
+        range_start = int(range_start)
+        range_end = int(range_end) if range_end else size-1
+        if range_start < 0 or range_end >= size or range_start >= range_end:
+            abort(416)
+
+        response = Response(
+                filecrypt.decrypt_generator(path, token, seek=range_start, end=range_end),
+                status = 206,
+                mimetype='application/octet-stream')
+        response.headers['Content-Range'] = f'bytes {range_start}-{range_end}/{size}'
+        response.headers['Content-Length'] = range_end - range_start + 1
+
+    response.headers['Accept-Ranges'] = 'bytes'
+    response.headers['Content-Disposition'] = f'attachment {filename}'
+    return response
+