Pad received signature with leading zeros when RSA key is used

1 files changed, 8 insertions, 1 deletions

diff --git a/paramiko/rsakey.py b/paramiko/rsakey.py
index d2dc99e4..1e2d5bfe 100644
--- a/paramiko/rsakey.py
+++ b/paramiko/rsakey.py
@@ -141,9 +141,16 @@ class RSAKey(PKey):
         if isinstance(key, rsa.RSAPrivateKey):
             key = key.public_key()
 
+        # NOTE: pad received signature with leading zeros, key.verify()
+        # expects a signature of key size (e.g. PuTTY doesn't pad)
+        sign = msg.get_binary()
+        diff = key.key_size - len(sign) * 8
+        if diff > 0:
+            sign = b"\x00" * ((diff + 7) // 8) + sign
+
         try:
             key.verify(
-                msg.get_binary(),
+                sign,
                 data,
                 padding.PKCS1v15(),
                 self.HASHES[sig_algorithm](),