[libsecret] mock: Pad the common secret with zero bytes to make it exactly 128 bytes long

[Stefan Walter <stefw src gnome org>]

commit d3ac1c183465bed5ce906062215734a76ac310c6
Author: Dmitry Shachnev <mitya57 gmail com>
Date:   Mon Oct 9 01:25:08 2017 +0700

    mock: Pad the common secret with zero bytes to make it exactly 128 bytes long
    
    This is what the C code does, see egg/egg-dh.c:340.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=768112

 libsecret/mock/service.py |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/libsecret/mock/service.py b/libsecret/mock/service.py
index 5fe6706..99f2cff 100644
--- a/libsecret/mock/service.py
+++ b/libsecret/mock/service.py
@@ -84,6 +84,8 @@ class AesAlgorithm():
                # print "mock publi: ", hex(publi)
                # print " mock peer: ", hex(peer)
                ikm = dh.derive_key(privat, peer)
+               # Pad the secret with zero bytes to match length of prime in bytes.
+               ikm = b'\x00' * (128 - len(ikm)) + ikm
                # print "  mock ikm: ", hex_encode(ikm)
                key = hkdf.hkdf(ikm, 16)
                # print "  mock key: ", hex_encode(key)