Fix BitString initialization via namedValues

[nekolyanich]

  class KeyUsage(BitString):
      namedValues = NamedValues(
          ('digitalSignature', 0),
          ('nonRepudiation', 1),
          ('keyEncipherment', 2),
          ('dataEncipherment', 3),
          ('keyAgreement', 4),
          ('keyCertSign', 5),
          ('cRLSign', 6),
          ('encipherOnly', 7),
          ('decipherOnly', 8),
      )

  encode(KeyUsage('keyCertSign,cRLSign')) != encode(KeyUsage("'0000011'B"))
                                                                    ^^
                                                                    ||
                                                bit #5 -------------+|
                                                bit #6 --------------+

[codecov-io]

Codecov Report

Merging #32 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
+ Coverage   82.03%   82.04%   +0.01%     
==========================================
  Files          25       25              
  Lines        3590     3593       +3     
==========================================
+ Hits         2945     2948       +3     
  Misses        645      645

Impacted Files	Coverage Δ
pyasn1/type/univ.py	77.92% <100%> (+0.05%)	⬆️

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[etingof]

Hey, thank you for your PR!

Would you mind explaining why do you think this KeyUsage('keyCertSign,cRLSign') should turn into 0000011 rather than into 1100000 as it currently does? Assuming keyCertSign is bit #5 and cRLSign is bit #6, both seem to reside where I'd expect them to, no?

Here is what happens when I run your test case over current master:

>>> KeyUsage('keyCertSign,cRLSign')
KeyUsage('1100000')
>>> encode(KeyUsage('keyCertSign,cRLSign')), encode(KeyUsage("'0000011'B"))
(b'\x03\x02\x01\xc0', b'\x03\x02\x01\x06')

[nekolyanich]

Thank you for quick response. Right encoded value for KeyUsage('keyCertSign,cRLSign') is b'\x03\x02\x01\x06'. For example GeoTrusts Global CA (RootCA for google.com) has this permissions in KeyUsage.

[nekolyanich]

FYI pyasn1-v0.2.2 have valid behavior

[etingof]

Ah, you are right! The ordering of the bits initializer is reversed compared to hex, for example. So I'm going to merge you fix now to make pyasn1readily operational.

Later on I'll look into optimizing out list operation (which is slow), add more tests to capture such regressions and push out a release.

Thank you!

[etingof]

So I refactored the fix a little. Hope to release 0.2.4 by the end of this week. Thank you!