TD0636: NIT Technical Decision for Clarification of Public Key User Authentication for SSH
ND SD2.2, FCS_SSHC_EXT.1
The NIT has issued a technical decision for clarification of public key user authentication for SSH.
NDcPP v2.2e, FCS_SSHC_EXT.1 ‘SSH Client’ shall be modified as follows:
FCS_SSHC_EXT.1.2 The TSF shall ensure that the SSH protocol implementation supports the following user authentication methods as described in RFC 4252: public key-based, [selection: password-based, no other method].
Application Note *
The intent of this element is to specify user authentication mechanism(s) that the TOE supports when acting as an SSH client. The TOE is required to implement the capability to generate userbased authentication keys in accordance with FCS_CKM.1 as specified by FMT_SMF.1 via “Ability to manage the cryptographic keys”. While no specific public key algorithms are mandatory to implement, the use of public key algorithms must be consistent with FCS_CKM.1, FCS_COP.1/Hash, and FCS_COP.1/SigGen.
If the TOE implements password-based authentication, the option ‘password-based’ must be selected. If the TOE can only authenticate itself with a public key, the option ‘no other method’ must be chosen.
FCS_SSHC_EXT.1.5 Application Note 93 shall be prepended with:
Application Note 93
The intent of this element is to specify peer (SSH server) authentication mechanism(s) that the TOE supports when acting as an SSH client. The TOE is required to implement the capability to verify the host’s public key as described in RFC 4251 Section 4.1.
ND SD v2.2, FCS_SSHC_EXT.1 ‘SSH Client’ TSS shall be modified as follows:
The evaluator shall check to ensure that the TSS contains a list of the public key algorithms that are acceptable for use for user authentication and that this list is consistent with asymmetric key generation algorithms selected in FCS_CKM.1, hashing algorithms selected in FCS_COP.1/Hash, and signature generation algorithms selected in FCS_COP.1/SigGen. The evaluator shall confirm the TSS is unambiguous in declaring the TOE’s ability to authenticate itself to a remote endpoint with a user-based public key.
If password-based authentication method has been selected in the FCS_SSHC_EXT.1.2, then the evaluator shall confirm it is also described in the TSS.
The evaluator shall confirm the TSS describes how a host-key public key (i.e., SSH server’s public key) is associated with the server identity.
The evaluator shall check the description of the implementation of this protocol in the TSS to ensure that optional characteristics are specified, and the host-key public key algorithms supported by the TOE are specified as well. The evaluator shall check the TSS to ensure that the host-key public key algorithms specified are identical to those listed for this component.
ND SD v2.2, FCS_SSHC_EXT.1 ‘SSH Client’ Guidance shall be modified as follows:
The evaluator shall check the guidance documentation to ensure that it contains instructions to the administrator on how to ensure that only the allowed mechanisms are used in SSH connections initiated by the TOE.
ND SD v2.2, FCS_SSHC_EXT.1.2 Tests shall be modified as follows:
Test objective: The purpose of these tests is to check the authentication of the client to the server using each claimed authentication method.
Test 1: For each claimed public-key authentication method, the evaluator shall configure the TOE to present a public key corresponding to that authentication method (e.g., 2048-bit RSA key when using ssh-rsa public key). The evaluator shall establish sufficient separate SSH connections with an appropriately configured remote non-TOE SSH server to demonstrate the use of all claimed public key algorithms. It is sufficient to observe the successful completion of the SSH Authentication Protocol to satisfy the intent of this test.
Test 2: [Conditional] If password-based authentication method has been selected in the FCS_SSHC_EXT.1.2, then following the guidance documentation the evaluator shall configure the TOE to perform password-based authentication with a remote SSH server to demonstrate that the TOE can successfully authenticate using a password as an authentication method.
For further information, please see NIT Interpretation at: https://www.niap-ccevs.org/Documents_and_Guidance/ccevs/NITDecisionRFI202115.pdf
See issue description.