From 54e7ffb6a57a05618965a3e14424514b1ebe3ca0 Mon Sep 17 00:00:00 2001
From: Roman Zeyde <me@romanzey.de>
Date: Fri, 27 Jan 2023 11:53:06 +0200
Subject: [PATCH] Allow prehashing for Minisign support

See https://github.com/jedisct1/minisign
---
 libagent/signify/__init__.py | 43 ++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/libagent/signify/__init__.py b/libagent/signify/__init__.py
index f7ad7ab..aa0ab5d 100644
--- a/libagent/signify/__init__.py
+++ b/libagent/signify/__init__.py
@@ -1,4 +1,4 @@
-"""TREZOR support for Ed25519 signify signatures."""
+"""TREZOR support for Ed25519 signify/minisign signatures."""
 
 import argparse
 import binascii
@@ -53,10 +53,14 @@ class Client:
             return sig, pubkey[1:]
 
 
-def format_payload(pubkey, data):
+ALG_SIGNIFY = b'Ed'
+ALG_MINISIGN = b'ED'  # prehashes the data before signing
+
+
+def format_payload(pubkey, data, sig_alg):
     """See http://www.openbsd.org/papers/bsdcan-signify.html for details."""
     keynum = hashlib.sha256(pubkey).digest()[:8]
-    return binascii.b2a_base64(b"Ed" + keynum + data).decode("ascii")
+    return binascii.b2a_base64(sig_alg + keynum + data).decode("ascii")
 
 
 def run_pubkey(device_type, args):
@@ -69,20 +73,33 @@ def run_pubkey(device_type, args):
     identity = _create_identity(user_id=args.user_id)
     pubkey = Client(device=device_type()).pubkey(identity=identity)
     comment = f'untrusted comment: identity {identity.to_string()}\n'
-    result = comment + format_payload(pubkey=pubkey, data=pubkey)
-    print(result, end="")
+    payload = format_payload(pubkey=pubkey, data=pubkey, sig_alg=ALG_SIGNIFY)
+    print(comment + payload, end="")
 
 
 def run_sign(device_type, args):
-    """Sign an input blob using Ed25519."""
+    """Prehash & sign an input blob using Ed25519."""
     util.setup_logging(verbosity=args.verbose)
     identity = _create_identity(user_id=args.user_id)
-    data = sys.stdin.buffer.read()
-    sig, pubkey = Client(device=device_type()).sign_with_pubkey(identity, data)
-    pubkey_str = format_payload(pubkey=pubkey, data=pubkey)
-    comment = f'untrusted comment: pubkey {pubkey_str}'
-    result = comment + format_payload(pubkey=pubkey, data=sig)
-    print(result, end="")
+
+    data_to_sign = sys.stdin.buffer.read()
+    sig_alg = ALG_SIGNIFY
+    if args.prehash:
+        # See https://github.com/jedisct1/minisign/commit/6e1023d20758b6fdb2a4b697213b0bf608ba4020
+        # Released in https://github.com/jedisct1/minisign/releases/tag/0.6
+        sig_alg = ALG_MINISIGN
+        data_to_sign = hashlib.blake2b(data_to_sign).digest()
+
+    sig, pubkey = Client(device=device_type()).sign_with_pubkey(identity, data_to_sign)
+    pubkey_str = format_payload(pubkey=pubkey, data=pubkey, sig_alg=sig_alg)
+    sig_str = format_payload(pubkey=pubkey, data=sig, sig_alg=sig_alg)
+    untrusted_comment = f'untrusted comment: pubkey {pubkey_str}'
+    print(untrusted_comment + sig_str, end="")
+
+    comment_to_sign = sig + args.comment.encode()
+    sig, _ = Client(device=device_type()).sign_with_pubkey(identity, comment_to_sign)
+    sig_str = binascii.b2a_base64(sig).decode("ascii")
+    print(f'trusted comment: {args.comment}\n' + sig_str, end="")
 
 
 def main(device_type):
@@ -100,6 +117,8 @@ def main(device_type):
     p = subparsers.add_parser('sign')
     p.add_argument('user_id')
     p.add_argument('-v', '--verbose', default=0, action='count')
+    p.add_argument('-c', '--comment', default=time.asctime())
+    p.add_argument('-H', '--prehash', default=False, action='store_true')
     p.set_defaults(func=run_sign)
 
     args = parser.parse_args()