[PATCH v2] SecureSocket: use fallback function if bit_length is not available in Python

[Jan Tluka]

Recently added SecureSocket feature brought dependency on Python 2.7
namely bit_length() method. Since we need to keep compatibility with
Python 2.6 that's on RHEL6 I added a fallback if bit_length is not
available. I compared the DH_GROUP and SRP_GROUP dicts both on Python2.6
and 2.7 and they had the same content (bit length), so this patch should
be safe.

Fixes issue 166.

Signed-off-by: Jan Tluka 
---
 lnst/Common/SecureSocket.py | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/lnst/Common/SecureSocket.py b/lnst/Common/SecureSocket.py
index b4ee8af..b856238 100644
--- a/lnst/Common/SecureSocket.py
+++ b/lnst/Common/SecureSocket.py
@@ -34,12 +34,21 @@ DH_GROUP = {"p": int("0xFFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"\
                      "15728E5A8AACAA68FFFFFFFFFFFFFFFF", 16),
             "g": 2}

+# to support both Python2.6 and 2.7, use following workaround to count
+# the bit length of a number; note that the workaround does not work for
+# value 0 but we don't use it for such value
+def bit_length(i):
+    try:
+        return i.bit_length()
+    except AttributeError:
+        return len(bin(i)) - 2
+
 DH_GROUP["q"] = (DH_GROUP["p"]-1)/2
-DH_GROUP["q_size"] = DH_GROUP["q"].bit_length()/8
-if DH_GROUP["q"].bit_length()%8:
+DH_GROUP["q_size"] = bit_length(DH_GROUP["q"])/8
+if bit_length(DH_GROUP["q"])%8:
     DH_GROUP["q_size"] += 1
-DH_GROUP["p_size"] = DH_GROUP["p"].bit_length()/8
-if DH_GROUP["p"].bit_length()%8:
+DH_GROUP["p_size"] = bit_length(DH_GROUP["p"])/8
+if bit_length(DH_GROUP["p"])%8:
     DH_GROUP["p_size"] += 1

SRP_GROUP = {"p": int("0xAC6BDB41324A9A9BF166DE5E1389582FAF72B6651987EE07FC"
@@ -55,11 +64,11 @@ SRP_GROUP = {"p": int("0xAC6BDB41324A9A9BF166DE5E1389582FAF72B6651987EE07FC"
              "g": 2}

SRP_GROUP["q"] = (SRP_GROUP["p"]-1)/2
-SRP_GROUP["q_size"] = SRP_GROUP["q"].bit_length()/8
-if SRP_GROUP["q"].bit_length()%8:
+SRP_GROUP["q_size"] = bit_length(SRP_GROUP["q"])/8
+if bit_length(SRP_GROUP["q"])%8:
     SRP_GROUP["q_size"] += 1
-SRP_GROUP["p_size"] = SRP_GROUP["p"].bit_length()/8
-if SRP_GROUP["p"].bit_length()%8:
+SRP_GROUP["p_size"] = bit_length(SRP_GROUP["p"])/8
+if bit_length(SRP_GROUP["p"])%8:
     SRP_GROUP["p_size"] += 1

class SecSocketException(Exception):

[Jan Tluka]

Mon, Mar 21, 2016 at 01:04:34PM CET, [e-mail] wrote:
> Recently added SecureSocket feature brought dependency on Python 2.7
> namely bit_length() method. Since we need to keep compatibility with
> Python 2.6 that's on RHEL6 I added a fallback if bit_length is not
> available. I compared the DH_GROUP and SRP_GROUP dicts both on Python2.6
> and 2.7 and they had the same content (bit length), so this patch should
> be safe.
>
> Fixes issue 166.
> Signed-off-by: Jan Tluka

FYI, I've just applied the patch.

-Jan