fix loading new openssh private key format when no padding

1 files changed, 23 insertions, 13 deletions

diff --git a/paramiko/pkey.py b/paramiko/pkey.py
index c6beef51..3a07426f 100644
--- a/paramiko/pkey.py
+++ b/paramiko/pkey.py
@@ -27,6 +27,7 @@ from hashlib import md5
 import re
 import struct
 
+import six
 import bcrypt
 
 from cryptography.hazmat.backends import default_backend
@@ -35,18 +36,29 @@ from cryptography.hazmat.primitives.ciphers import algorithms, modes, Cipher
 
 from paramiko import util
 from paramiko.common import o600
-from paramiko.py3compat import (
-    u,
-    encodebytes,
-    decodebytes,
-    b,
-    string_types,
-    byte_ord,
-)
+from paramiko.py3compat import u, b, encodebytes, decodebytes, string_types
 from paramiko.ssh_exception import SSHException, PasswordRequiredException
 from paramiko.message import Message
 
 
+OPENSSH_AUTH_MAGIC = b"openssh-key-v1\x00"
+
+
+def _unpad_openssh(data):
+    # At the moment, this is only used for unpadding private keys on disk. This
+    # really ought to be made constant time (possibly by upstreaming this logic
+    # into pyca/cryptography).
+    padding_length = six.indexbytes(data, -1)
+    if 0x20 <= padding_length < 0x7f:
+        return data  # no padding, last byte part comment (printable ascii)
+    if padding_length > 15:
+        raise SSHException("Invalid key")
+    for i in range(padding_length):
+        if six.indexbytes(data, i - padding_length) != i + 1:
+            raise SSHException("Invalid key")
+    return data[:-padding_length]
+
+
 class PKey(object):
     """
     Base class for public keys.
@@ -395,8 +407,8 @@ class PKey(object):
             raise SSHException("base64 decoding error: {}".format(e))
 
         # read data struct
-        auth_magic = data[:14]
-        if auth_magic != b("openssh-key-v1"):
+        auth_magic = data[:15]
+        if auth_magic != OPENSSH_AUTH_MAGIC:
             raise SSHException("unexpected OpenSSH key header encountered")
 
         cstruct = self._uint32_cstruct_unpack(data[15:], "sssur")
@@ -466,9 +478,7 @@ class PKey(object):
                 "OpenSSH private key file checkints do not match"
             )
 
-        # Remove padding
-        padlen = byte_ord(keydata[len(keydata) - 1])
-        return keydata[: len(keydata) - padlen]
+        return _unpad_openssh(keydata)
 
     def _uint32_cstruct_unpack(self, data, strformat):
         """