From 367aac5fa4073a925b24bd3bc8ac2105fea63cfe Mon Sep 17 00:00:00 2001
From: Linus Nordberg <linus@nordberg.se>
Date: Fri, 25 Mar 2022 14:38:07 +0100
Subject: sign tree head using SSHSIG
---
sigsum-witness.py | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/sigsum-witness.py b/sigsum-witness.py
index 2be3f3a..52005df 100755
--- a/sigsum-witness.py
+++ b/sigsum-witness.py
@@ -29,6 +29,7 @@ from hashlib import sha256
import time
from math import floor
from pathlib import PurePath
+from tools.libsigntools import ssh_to_sign
BASE_URL_DEFAULT = 'http://poc.sigsum.org:4780/'
CONFIG_DIR_DEFAULT = os.path.expanduser('~/.config/sigsum-witness/')
@@ -140,12 +141,12 @@ class TreeHead:
text += 'signature={}\n'.format(self._text['signature'])
return text.encode('ascii')
- def serialise(self, pubkey):
- data = struct.pack('!QQ', self.timestamp, self.tree_size)
- data += unhexlify(self._text['root_hash'])
- data += sha256(pubkey.encode()).digest()
- assert(len(data) == 8 + 8 + 32 + 32)
- return data
+ def to_signed_data(self, pubkey):
+ namespace = 'tree_head:v0:{}@sigsum.org'.format(hexlify(sha256(pubkey.encode()).digest()).decode())
+ msg = struct.pack('!QQ', self.timestamp, self.tree_size)
+ msg += unhexlify(self._text['root_hash'])
+ assert(len(msg) == 8 + 8 + 32)
+ return ssh_to_sign(namespace, 'sha256', sha256(msg).digest())
def signature_valid(self, pubkey):
# Guard against tree head with >1 signature -- don't try to
@@ -153,7 +154,7 @@ class TreeHead:
assert(type(self._text['signature']) is str)
sig = unhexlify(self._text['signature'])
assert(len(sig) == 64)
- data = self.serialise(pubkey)
+ data = self.to_signed_data(pubkey)
try:
verified_data = pubkey.verify(sig + data)
except nacl.exceptions.BadSignatureError:
@@ -348,7 +349,7 @@ def consistency_proof_valid(first, second, proof):
return sn == 0 and fr == first.root_hash and sr == second.root_hash
def sign_send_store_tree_head(signing_key, log_key, tree_head):
- signature = signing_key.sign(tree_head.serialise(log_key)).signature
+ signature = signing_key.sign(tree_head.to_signed_data(log_key)).signature
hash = sha256(signing_key.verify_key.encode())
post_data = 'cosignature={}\n'.format(hexlify(signature).decode('ascii'))
--
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