Bug 1393431 – CVE-2016-9243 python-cryptography: HKDF might return an empty byte-string

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Bug 1393431 - (CVE-2016-9243) CVE-2016-9243 python-cryptography: HKDF might return an empty byte-string

Summary:	CVE-2016-9243 python-cryptography: HKDF might return an empty byte-string

Status:	NEW

Aliases:	CVE-2016-9243

Product:	Security Response
Classification:	Other
Component:	vulnerability (Show other bugs)
Sub Component:
Version:	unspecified
Hardware:	All Linux

Priority	low Severity low
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Assigned To:	Red Hat Product Security
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Whiteboard:	impact=low,public=20161105,reported=2...
Keywords:	Security

Depends On:	1393432
Blocks:	1393433
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Reported:	2016-11-09 09:36 EST by Andrej Nemec
Modified:	2018-04-30 18:15 EDT (History)
CC List:	18 users (show)

See Also:
Fixed In Version:	python-cryptography 1.5.3
Doc Type:	If docs needed, set a value
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Description Andrej Nemec 2016-11-09 09:36:53 EST

Cryptography 1.5.3 release fixed one security issue.

HKDF would return an empty byte-string if used with a length less than algorithm.digest_size.

References:

https://cryptography.io/en/latest/changelog/#id1

Upstream bug:

https://github.com/pyca/cryptography/issues/3211

Upstream patch:

https://github.com/pyca/cryptography/commit/b924696b2e8731f39696584d12cceeb3aeb2d874

Comment 1 Andrej Nemec 2016-11-09 09:37:29 EST

Created python-cryptography tracking bugs for this issue:

Affects: fedora-all [bug 1393432]

Comment 2 Huzaifa S. Sidhpurwala 2016-11-10 02:57:20 EST

Data returned by the HKDF() are deemed to be cryptographically strong keys, which can be used by other cryptrographical primitives like ciphers to encrypt secret data. When HKDF() returns empty strings, then depending on the primitive used, it could mean weak encryption or perhaps no encryption at all.

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