Changes/OpenSSH Crypto Policy

OpenSSH Crypto Policy (Client)

Summary

OpenSSH client will follow system-wide crypto policies already followed by other cryptographic libraries and tools. It will allow to use different security levels defined system-wide.

Owner

• Name: Jakub Jelen
• Email: jjelen@redhat.com
• Release notes owner:

Current status

• Targeted release: Fedora 26
• Last updated: 2016-10-17
• Tracker bug: #1385506

Detailed Description

Currently, the set of cryptographic algorithms used in OpenSSH is defined by upstream and Fedora just inherits what upstream considers secure. If there are special requirements for the security, manual modifications of the configuration files is required, which also prevents package manager to update the configuration file with future updates and can possibly leave enabled insecure algorithms.

Since Fedora 25 we have possibility to include configuration files from the main ssh_config, which allowed us to include crypto policies in the OpenSSH (client).

For more information about Crypto Policy, see the appropriate wiki page Changes/CryptoPolicy describing the concept in whole.

Benefit to Fedora

OpenSSH will follow system-wide crypto policy generated by update-crypto-policies(8) to ensure uniform security levels in the whole system.

The client side configuration has always priority in the negotiation of cryptographic algorithms in the SSH session, which makes users sure they are using secure algorithms in their communiques are secret.

Scope

• Proposal owners: Default OpenSSH configuration will include the generated policy file containing the definition of system-wide enabled algorithms. The include must be before any other options so user changes would not unintentionally get used instead of system-wide policy. The policy preview is already available in the pull request on github

• Other developers: N/A (not a System Wide Change)

• Release engineering: N/A (not a System Wide Change)
  • List of deliverables: N/A (not a System Wide Change)

• Policies and guidelines: N/A (not a System Wide Change)

• Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

The default configuration files will be updated to include policy files and the default list of Ciphers, Key Exchange algorithms and MACs will be updated according to system-wide default (the changes are minor). If you previously modified your configuration files (/etc/ssh/ssh_config), they will not be overwritten and you will need to merge them from .rpmnew file.

You can always overwrite the system-wide policy using user-specific configuration files in ~/.ssh/config or on the command line.

How To Test

• All the SSH use cases should work after the update without any significant change, for example using QA:Testcase_OpenSSH
  • In the verbose log (with -vv switches) or in the output of ssh -G test | grep "kex\|ciphers\|macs", you should see a long list with many algorithms
    • There are Key exchange algorithms using SHA1: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1
    • There are MACs algorithms using SHA1: hmac-sha1
• Set higher security level:
  • Run update-crypto-policies --set FUTURE
• Test the functionality again, for example using QA:Testcase_OpenSSH
  • In the verbose log (with -vv switches) or in the output of ssh -G test | grep "kex\|ciphers\|macs", you should see shorter list with stronger algorithms
    • There should not be any sha1 hash functions
    • There should not be 3des-cbc cipher
    • There should not be any 64 bits MACs, such as umac-64-etm@openssh.com,umac-64@openssh.com,hmac-md5
• Reset the security level to the DEFAULT
  • Run update-crypto-policies --set DEFAULT

In case you do not see any difference after the policy should have been updated, make sure your /etc/ssh/ssh_config.d/05-redhat.conf file contains, close to the start of the file, a line

Include /etc/crypto-policies/back-ends/openssh.txt

and the file /etc/ssh/ssh_config contains a line

Include /etc/ssh/ssh_config.d/*.conf

N/A (not a System Wide Change)

User Experience

N/A (not a System Wide Change)

Dependencies

N/A (not a System Wide Change)

Contingency Plan

• Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
• Contingency deadline: N/A (not a System Wide Change)
• Blocks release? N/A (not a System Wide Change), Yes/No
• Blocks product? product

Documentation

Upstream documentation is available in the upstream repository for update-crypto-policies(8).

N/A (not a System Wide Change)