WIP cryptographic design

1 files changed, 143 insertions, 0 deletions

diff --git a/controller/fw/tools/presig_gen.py b/controller/fw/tools/presig_gen.py
new file mode 100644
index 0000000..2d97391
--- /dev/null
+++ b/controller/fw/tools/presig_gen.py
@@ -0,0 +1,143 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+import textwrap
+import uuid
+import hashlib
+import binascii
+import sqlite3
+import time
+
+import nacl.signing
+import nacl.encoding
+
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.backends import default_backend
+
+
+PRESIG_VERSION = '000.001'
+
+def format_hex(data, indent=4, wrap=True):
+    indent = ' '*indent
+    par = ', '.join(f'0x{b:02x}' for b in data)
+    par = textwrap.fill(par, width=120,
+        initial_indent=indent, subsequent_indent=indent,
+        replace_whitespace=False, drop_whitespace=False)
+    if wrap:
+        return f'{{\n{par}\n}}'
+    return par
+
+def domain_string(domain_name, value, serial):
+    return f'smart reset domain string v{PRESIG_VERSION}: domain:{domain_name}={value}@{serial}'
+
+if __name__ == '__main__':
+    import argparse
+    parser = argparse.ArgumentParser()
+    parser.add_argument('keyfile', help='Key file to use')
+    parser.add_argument('presig_db', nargs='?', help='sqlite3 dbfile for generated presig authorization keys')
+    parser.add_argument('-g', '--generate', action='store_true', help='Generate signing keypair')
+    parser.add_argument('-v', '--vendor', type=str, default='Darthenschmidt Cyberei und Verschleierungstechnik GmbH', help='Vendor name for vendor domain')
+    parser.add_argument('-s', '--series', type=str, default='Frobnicator v0.23.7', help='Series identifier for series domain')
+    parser.add_argument('-r', '--region', type=str, default='Neuland', help='Region name for region domain')
+    parser.add_argument('-c', '--country', type=str, default='Germany', help='Country name for country domain')
+    parser.add_argument('-p', '--start-serial', type=int, default=0, help='First presig serial number to use')
+    parser.add_argument('-n', '--presig-count', type=int, default=3, help='Number of presigs to generate')
+    parser.add_argument('-i', '--iv', type=str, default='safety reset oob presig iv', help='IV for presig generation')
+    args = parser.parse_args()
+
+    if args.generate:
+        if os.path.exists(args.keyfile):
+            print("Error: keyfile already exists. We won't overwrite it. Instead please remove it manually.",
+                    file=sys.stderr)
+            sys.exit(1)
+        signing_key = nacl.signing.SigningKey.generate()
+        with open(args.keyfile, 'wb') as f:
+            f.write(signing_key.encode(encoder=nacl.encoding.Base64Encoder))
+            f.write(b'\n')
+        sys.exit(0)
+
+    with open(args.keyfile, 'r') as f:
+        signing_key = nacl.signing.SigningKey(f.read().strip(), encoder=nacl.encoding.Base64Encoder)
+        pubkey_bytes = signing_key.verify_key.encode(encoder=nacl.encoding.RawEncoder)
+        pubkey_hash = hashlib.sha512(pubkey_bytes).digest()[:16]
+
+    if not args.presig_db:
+        print('The presig_db parameter is required.', file=sys.stderr)
+        sys.exit(1)
+
+    db = sqlite3.connect(args.presig_db)
+    db.execute('CREATE TABLE IF NOT EXISTS presig_authkey (timestamp, pubkey_hash, bundle_id, presig_ver, domain, value, serial, authkey)')
+
+    bundle_id = uuid.uuid4().bytes
+
+    print('#include <stdint.h>')
+    print('#include <assert.h>')
+    print()
+    print('#include "crypto.h"')
+    print()
+
+    print(f'/* bundle id {binascii.hexlify(bundle_id).decode()} */')
+    print(f'uint8_t presig_bundle_id[16] = {format_hex(bundle_id)};')
+    print(f'int presig_first_serial = {args.start_serial};')
+    print()
+
+    print(f'uint8_t oob_trigger_pubkey[crypto_sign_PUBLICKEYBYTES] = {format_hex(pubkey_bytes)};')
+    print()
+
+    print('uint8_t presig_messages[_TRIGGER_DOMAIN_COUNT][PRESIG_STORE_SIZE][PRESIG_MSG_LEN] = {')
+    device_domains = {
+            'all': 'all',
+            'country': args.country,
+            'region': args.region,
+            'vendor': args.vendor,
+            'series': args.series
+            }
+    presigs = { dom: [] for dom in device_domains }
+    for dom, val in device_domains.items():
+        print('    {')
+        for i in range(args.presig_count):
+            serial = args.start_serial + i
+            ds = domain_string(dom, val, serial)
+            ds_hash = hashlib.sha512(ds.encode()).digest()[:16]
+            presigs[dom].append((ds_hash, val, serial))
+            print(f'        {{ /* "{ds}" */')
+            print(format_hex(ds_hash, indent=8, wrap=False))
+            print(f'        }},')
+        print('    },')
+    print('};')
+    print()
+
+    presig_iv = hashlib.sha512(args.iv.encode()).digest()[:16]
+    print(f'uint8_t oob_presig_iv[16] = {{ /* sha512("{args.iv}")[:16] */')
+    print(format_hex(presig_iv, wrap=False))
+    print(f'}};')
+    print()
+
+
+    print('uint8_t presig_store[_TRIGGER_DOMAIN_COUNT][PRESIG_STORE_SIZE][crypto_sign_BYTES] = {')
+    for dom, hashes in presigs.items():
+        print(f'    {{ /* domain {dom} */')
+
+        for ds_hash, val, serial in hashes:
+            authkey = os.urandom(16)
+            cipher = Cipher(algorithms.AES(authkey), modes.CTR(presig_iv), backend=default_backend())
+            enc = cipher.encryptor()
+            ciphertext = enc.update(ds_hash)
+            assert len(enc.finalize()) == 0
+
+            with db:
+                db.execute('INSERT INTO presig_authkey VALUES (?, ?, ?, ?, ?, ?, ?, ?)',
+                        (int(time.time()*1000), pubkey_hash, binascii.hexlify(bundle_id).decode(), PRESIG_VERSION, dom,
+            print(format_hex(ciphertext, indent=8, wrap=False))
+            print(f'        }},')
+
+        print(f'    }},')
+    print(f'}};')
+
+    print()
+    print('static inline void __hack_asserts_only(void) {')
+    print(f'    static_assert(_TRIGGER_DOMAIN_COUNT == {len(presigs)});')
+    print(f'    static_assert(PRESIG_STORE_SIZE == {args.presig_count});')
+    print('}')
+    print()