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Revert a regression in DSS key generation 

A change in f0017b8330 caused a random regression in DSS key signing
due to moving the padding on the integers generated by DSA from the left
to the right.

So, for example, if signing the test case string "jerri blank", the
random number might be generated as:

k=703745698612177278239572677252380378525350342103

If so, the signature parts will be:
r=184615963997659989901526712385095827509599268253
s=2682547683721156713440053885014828604195555319

Note the s being shorter.

Prior to f0017b8330, s would be right-padded with zeros:
s=268254768372115671344005388501482860419555531900

After, it would be left-padded:
s=002682547683721156713440053885014828604195555319

When converting back to a long, that loses the padding. This change
restores the behaviour.

Fixes #308
This commit is contained in:
Chris Rose 2014-04-14 17:38:05 -04:00
parent ab08ef6651
commit 34d03ae3dc
2 changed files with 4 additions and 2 deletions
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4
paramiko/dsskey.py
View File

@ -111,9 +111,9 @@ class DSSKey (PKey):
rstr = util.deflate_long(r, 0) rstr = util.deflate_long(r, 0)
sstr = util.deflate_long(s, 0) sstr = util.deflate_long(s, 0)
if len(rstr) < 20: if len(rstr) < 20:
rstr += zero_byte * (20 - len(rstr)) rstr = zero_byte * (20 - len(rstr)) + rstr
if len(sstr) < 20: if len(sstr) < 20:
sstr += zero_byte * (20 - len(sstr)) sstr = zero_byte * (20 - len(sstr)) + sstr
m.add_string(rstr + sstr) m.add_string(rstr + sstr)
return m return m

2
sites/www/changelog.rst
View File

@ -2,6 +2,8 @@
Changelog Changelog
========= =========
* :bug:`308` Fix regression in dsskey.py that caused sporadic signature
verification failures. Thanks to Chris Rose.
* :support:`290` (also :issue:`292`) Add support for building universal * :support:`290` (also :issue:`292`) Add support for building universal
(Python 2+3 compatible) wheel files during the release process. Courtesy of (Python 2+3 compatible) wheel files during the release process. Courtesy of
Alex Gaynor. Alex Gaynor.