Bug 1479270

Summary:	New default cipher in OpenVPN
Product:	[Fedora] Fedora	Reporter:	Jan Kurik <jkurik>
Component:	Changes Tracking	Assignee:	David Sommerseth <dazo>
Status:	CLOSED CURRENTRELEASE	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	27	CC:	dazo
Target Milestone:	---	Flags:	dazo: fedora_requires_release_note+
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:	ChangeAcceptedF27, SelfContainedChange
Fixed In Version:		Doc Type:	Enhancement
Doc Text:	Feature: Change of default cipher algorithm Reason: The current default cipher in OpenVPN uses BF-CBC (Blowfish) which is considered a very weak cipher these days, especially after the SWEET32 issue (https://sweet32.info/) which was publicised in 2016. Result: OpenVPN v2.4 supports a fairly simple negotiation of crypto parameters. This allows OpenVPN to let clients connect using independent cipher settings. This change will only affect OpenVPN servers using the openvpn-server@.service unit file. This change moves the default cipher to AES-256-GCM while keeping backwards compatibility to older clients not supporting GCM to connect using either BF-CBC, AES-128-CBC or AES-256-CBC. If --cipher is not provided in the client OpenVPN configuration file, BF-CBC will be used as the default. Those client configurations can be updated on a one-by-one approach to use at least --cipher AES-128-CBC or --cipher AES-256-CBC. For any clients running OpenVPN v2.4 or newer, they will by default switch to AES-256-GCM automatically regardless of the --cipher values. This behaviour can be overridden on the server side by changing/adding --cipher to the configuration file. The list of ciphers being allowed can be modified by changing/adding --ncp-ciphers.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-11-14 08:58:41 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Jan Kurik 2017-08-08 08:42:10 UTC

This is a tracking bug for Change: New default cipher in OpenVPN
For more details, see: https://fedoraproject.org//wiki/Changes/New_default_cipher_in_OpenVPN

Since the discovery of the SWEET32 flaw, ciphers using cipher-blocks smaller than 128-bits are considered vulnerable and should not be used any more.  OpenVPN uses Blowfish (BF-128-CBC) as the default cipher, which is hit by the SWEET32 flaw.  This proposal changes the default cipher to AES-256-GCM while in parallel allowing clients to connect using AES-256-CBC, AES-128-CBC or the deprecated BF-CBC,

Comment 1 David Sommerseth 2017-08-08 10:16:19 UTC

This change is applied to openvpn-2.4.3-4.fc27 (master branch)

https://koji.fedoraproject.org/koji/buildinfo?buildID=951059

Comment 2 Jan Kurik 2017-08-15 08:07:10 UTC

This bug appears to have been reported against 'rawhide' during the Fedora 27 development cycle.
Changing version to '27'.

Comment 3 Jan Kurik 2017-09-06 13:38:34 UTC

On 2017-Sep-05 we reached the "Change Checkpoint: 100% Code Complete Deadline" milestone for Fedora 27 release. At this point all the Changes not at least in "ON_QA" state should be brought to FESCo for review. Please update the state of this bug to "ON_QA" if it is already 100% completed. Please let me know in case you have any trouble with the implementation and the Change needs any help or review.

Thanks, Jan

Comment 4 David Sommerseth 2017-09-06 15:02:21 UTC

commit b931012953451b2614b5fdfa5afe3c1d47c42fe8
Author: David Sommerseth <dazo>
Date:   Tue Jul 4 16:17:37 2017 +0200

    Change default cipher for server configurations to AES-GCM
    
    At the same time, utilize the Negotiable Crypto Parameters (NCP) feature
    in OpenVPN v2.4, which allows clients using the old BF-CBC default cipher
    to connect without any issues.
    
    F-27 Change request: https://fedoraproject.org/wiki/Changes/New_default_cipher_in_OpenVPN
    
    This change was approved in the FESCO meeting 2017-08-04.
    
    Also fix a truncated changelog entry for openvpn-2.4.3-1


$ git branch --contains b931012953451b2614b5fdfa5afe3c1d47c42fe8
* f27
  master
$