Secure Shell and FIPS 140-2

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The openssh implementation of Secure Shell is a consumer of the OpenSSL FIPS 140-2 module. If your system must comply with FIPS 140-2 requirements, you need to configure and use the FIPS 140-2 options.

OpenSSH in Oracle Solaris sets FIPS 140-2 mode dynamically. If the OpenSSL library that OpenSSH links with is FIPS 140-2 capable, OpenSSH runs in FIPS 140-2 mode. For information, see Example of Running in FIPS 140-2 Mode on an Oracle Solaris 11.4 System in Using a FIPS 140-2 Enabled System in Oracle Solaris 11.4. In a change from the SunSSH implementation, the administrator is not required to explicitly enable FIPS 140-2 mode, so the UseFips140 configuration option does not exist.

To confirm that OpenSSH is running in FIPS 140-2 mode, check for a FIPS suffix in the OpenSSH version string. This information is indicated in debug messages, as shown in this example:

jdoe:~$ ssh -vvv localhost date 2>&1 | grep -i fips
 OpenSSH_7.7p1, OpenSSL 1.0.2r-fips Mar 2019
 debug3: Running in FIPS mode.
 debug1: /etc/ssh/ssh_config line 33: Deprecated option "usefips140"
 debug1: Local version string SSH-2.0-OpenSSH_7.7 FIPS
 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.7 FIPS
 debug1: match: OpenSSH_7.7 FIPS pat OpenSSH* compat 0x04000000
 debug3: Temporarily unsetting FIPS mode to compute MD5 for GSS-API key exchange method names
 debug3: Running in FIPS mode.

FIPS 140-2 Approved Algorithms for OpenSSH

When running in FIPS 140-2 mode, only FIPS 140-2 approved ciphers, message authentication codes (MACs), and digests are allowed.

You can use the following commands to list all supported ciphers and MACs:

$ ssh -Q cipher
$ ssh -Q mac

Ciphers, MACs and digests that are not FIPS 140-2 approved are disabled in FIPS 140-2 mode. Attempts to use non-approved algorithms fail, as shown in this example:

jdoe:~$ ssh -c arcfour somehost
 Unknown cipher type 'arcfour'

To list OpenSSL ciphers, use the following command:

$ openssl ciphers -v

FIPS 140-2 Approved Key Formats and Sizes for OpenSSH

Administrators must use key formats and key sizes that are approved for FIPS 140-2.

The following FIPS 140-2 approved key types and key sizes are supported in OpenSSH:

ed25519
For ssh-rsa, the following key sizes are supported:
```
1024
2048
3072
```

Use of a weak key can result in a failure in FIPS 140-2 mode as shown in the following example:

root@S12-91:~# ssh -i rsa512 localhost
 sign_and_send_pubkey: signing failed: error:04066078:rsa
routines:RSA_EAY_PRIVATE_ENCRYPT:key size too small

For more information about FIPS 140-2, review the following:

Using a FIPS 140-2 Enabled System in Oracle Solaris 11.4
ssh(1)
sshd(8)
sshd_config (5) and ssh_config (5) man pages, viewed with the man command