Fallback to sha1 in _compute_key

1 files changed, 3 insertions, 1 deletions

diff --git a/paramiko/transport.py b/paramiko/transport.py
index d2fccf07..98b810ee 100644
--- a/paramiko/transport.py
+++ b/paramiko/transport.py
@@ -1534,7 +1534,9 @@ class Transport (threading.Thread, ClosingContextManager):
         m.add_bytes(self.H)
         m.add_byte(b(id))
         m.add_bytes(self.session_id)
-        hash_algo = self.kex_engine.hash_algo
+        # Fallback to SHA1 for kex engines that fail to specify a hex
+        # algorithm, or for e.g. transport tests that don't run kexinit.
+        hash_algo = getattr(self.kex_engine, 'hex_algo', sha1)
         out = sofar = hash_algo(m.asbytes()).digest()
         while len(out) < nbytes:
             m = Message()