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TD0164:  NIT Technical Decision for Negative testing for additional ciphers for SSH

Publication Date
2017.03.21

Protection Profiles
CPP_ND_V1.0

Other References
ND SD V1.0, FCS_SSHC_EXT.1.4, FCS_SSHS_EXT.1.4

Issue Description

The Network Interpretations Team (NIT) has issued a technical decision regarding negative testing for additional ciphers for SSH.

Resolution

The evaluator must ensure that only claimed ciphers and cryptographic primitives are used to establish a SSH connection. To verify this, the evaluator shall start session establishment for a SSH connection with a remote server (for FCS_SSHC_EXT.1.4) or from remote client (for FCS_SSHS_EXT.1.4), respectively (referred to as 'remote endpoint' below). The evaluator shall capture the traffic exchanged between the TOE and the remote endpoint during protocol negotiation (e.g. using a packet capture tool or information provided by the endpoint, respectively). The evaluator shall verify from the captured traffic that the TOE offers all the ciphers defined in the TSS for the TOE for SSH sessions, but no additional ones compared to the definition in the TSS. The evaluator shall perform one successful negotiation of an SSH session to verify that the TOE behaves as expected. It is sufficient to observe the successful negotiation of the session to satisfy the intent of the test. If the evaluator detects that not all ciphers defined in the TSS for SSH are supported by the TOE and/or the TOE supports one or more additional ciphers not defined in the TSS for SSH, the test shall be regarded as failed. 

To align with NIT interpretation # 201613 the test definition in ND SD V1.0 for FCS_SSHC_EXT.1.4 and FCS_SSHS_EXT.1.4 are updated as follows:  

FCS_SSHC_EXT.1.4

Test 1: The evaluator shall establish a SSH connection using each of the encryption algorithms specified by the requirement. It is sufficient to observe (on the wire) the successful negotiation of the algorithm to satisfy the intent of the test.

Test 2: The evaluator shall configure an SSH server to only allow an encryption algorithm that is not included in the ST selection. The evaluator shall attempt to establish an SSH connection from the TOE to the SSH server and observe that the connection is rejected.

FCS_SSHS_EXT.1.4

Test 1: The evaluator shall establish a SSH connection using each of the encryption algorithms specified by the requirement. It is sufficient to observe (on the wire) the successful negotiation of the algorithm to satisfy the intent of the test.

Test 2: The evaluator shall configure an SSH client to only allow an encryption algorithm that is not included in the ST selection. The evaluator shall attempt to establish an SSH connection from the SSH client to the TOE and observe that the connection is rejected.

For further information, please see the NIT interpretation at: https://www.niap-ccevs.org/Documents_and_Guidance/ccevs/NITDecisionRfi13.pdf.  

In addition, reference ND Supporting Document v1-1 on the Network Fundamentals and Firewall Technical Community website). The iTC has determined that the draft changes reviewed during the public comment period were accepted and will be incorporated into ND cPP V2.0. 

Justification

See issue description

 
 
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