Cisco IOS XE X.509v3 Certificates for SSH Authentication Configuration Guide PDF

Restrictions for X.509v3 Certificates for SSH Authentication

X.509v3 Certificates for SSH Authentication The X.509v3 Certificates for SSH Authentication feature uses the X.509v3 digital certificates in server and user authentication at the secure shell (SSH) server side. This module describes how to configure server and user certificate profiles for a digital certificate.

Prerequisites for X.509v3 Certificates for SSH Authentication, on page 1 Restrictions for X.509v3 Certificates for SSH Authentication, on page 1 Information About X.509v3 Certificates for SSH Authentication, on page 2 How to Configure X.509v3 Certificates for SSH Authentication, on page 2 Verifying Configuration for Server and User Authentication Using Digital Certificates, on page 7 Configuration Examples for X.509v3 Certificates for SSH Authentication, on page 8 Feature History for X.509v3 Certificates for SSH Authentication, on page 8 Prerequisites for X.509v3 Certificates for SSH Authentication • The X.509v3 Certificates for SSH Authentication feature introduces the ip ssh server algorithm authentication command to replace the ip ssh server authenticate user command.

If you use the ip ssh server authenticate user command, the following deprecation message is displayed. Warning: SSH command accepted but this CLI will be deprecated soon. Please move to new CLI ssh server algorithm authentication”. Please configure “default ip ssh server authenticate user” to make the CLI ineffective. Use the default ip ssh server authenticate user command to remove the ip ssh server authenticate user command from effect. The IOS secure shell (SSH) server then starts using the ip ssh server algorithm authentication command.

Restrictions for X.509v3 Certificates for SSH Authentication • The X.509v3 Certificates for SSH Authentication feature implementation is applicable only on the Cisco IOS XE secure shell (SSH) server side. • The SSH server supports only the x509v3-ssh-rsa algorithm-based certificate for server and user authentication. X.509v3 Certificates for SSH Authentication 1

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Configuring the SSH Server to Use Digital Certificates for Server Authentication

Information About X.509v3 Certificates for SSH Authentication The following section provides information about digital certificates, and server and user authentication. Digital Certificates The validity of the authentication depends upon the strength of the linkage between the public signing key and the identity of the signer. Digital certificates in the X.509v3 format (RFC5280) are used to provide identity management. A chain of signatures by a trusted root certification authority and its intermediate certificate authorities binds a given public signing key to a given digital identity. Public key infrastructure (PKI) trustpoint helps manage the digital certificates.

The association between the certificate and the trustpoint helps track the certificate. The trustpoint contains information about the certificate authority (CA), different identity parameters, and the digital certificate. Multiple trustpoints can be created to associate with different certificates. Server and User Authentication using X.509v3 For server authentication, the Cisco IOS XE secure shell (SSH) server sends its own certificate to the SSH client for verification. This server certificate is associated with the trustpoint configured in the server certificate profile (ssh-server-cert-profile-server configuration mode).

For user authentication, the SSH client sends the user's certificate to the SSH server for verification. The SSH server validates the incoming user certificate using public key infrastructure (PKI) trustpoints configured in the server certificate profile (ssh-server-cert-profile-user configuration mode). By default, certificate-based authentication is enabled for server and user at the SSH server end. How to Configure X.509v3 Certificates for SSH Authentication The following section provides information about how to configure X.509v3 Certificates for SSH Authentication.

ConfiguringtheSSHServertoUseDigitalCertificatesforServerAuthentication To configure the SSH server to use digital certificates for server authentication, perform this procedure: Procedure X.509v3 Certificates for SSH Authentication Information About X.509v3 Certificates for SSH Authentication Command or Action Purpose Step 1 enable Example: Device> enable Enables privileged EXEC mode. Enter your password, if prompted. Step 2 configure terminal Example: Enters global configuration mode. X.509v3 Certificates for SSH Authentication 2

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Configuring the SSH Server to Verify Digital Certificates for User Authentication

ConfiguringtheSSHServertoVerifyDigitalCertificatesforUserAuthentication To configure the SSH Server to use digital certificates for user authentication, perform this procedure: X.509v3 Certificates for SSH Authentication Configuring the SSH Server to Verify Digital Certificates for User Authentication Command or Action Purpose Device# configure terminal Step 3 ip ssh server algorithm hostkey {x509v3-ssh-rsa [ssh-rsa] | ssh-rsa [x509v3-ssh-rsa]} Example: Device(config)# ip ssh server algorithm hostkey x509v3-ssh-rsa Defines the order of host key algorithms. Only the configured algorithm is negotiated with the secure shell (SSH) client.

Note The IOS SSH server must have at least one configured host key algorithm: • ssh-rsa: public key based authentication • x509v3-ssh-rsa: certificate-based authentication Step 4 ip ssh server certificate profile Example: Device(config)# ip ssh server certificate profile Configures server certificate profile and user certificate profile and enters SSH certificate profile configuration mode. Step 5 server Example: Device(ssh-server-cert-profile)# server Configures server certificate profile and enters SSH server certificate profile server configuration mode. Step 6 trustpoint sign PKI-trustpoint-name Example:

Device(ssh-server-cert-profile-server)# trustpoint sign trust1 Attaches the public key infrastructure (PKI) trustpoint to the server certificate profile. The SSH server uses the certificate associated with this PKI trustpoint for server authentication. Step 7 ocsp-response include Example: Device(ssh-server-cert-profile-server)# ocsp-response include (Optional) Sends the Online Certificate Status Protocol (OCSP) response or OCSP stapling along with the server certificate. Note By default the no form of this command is configured and no OCSP response is sent along with the server certificate. Step 8 end Example:

Device(ssh-server-cert-profile-server)# end Exits SSH server certificate profile server configuration mode and returns to privileged EXEC mode. X.509v3 Certificates for SSH Authentication 3

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Configuring the SSH Server to Verify Digital Certificates for User Authentication

Procedure X.509v3 Certificates for SSH Authentication Configuring the SSH Server to Verify Digital Certificates for User Authentication Command or Action Purpose Step 1 enable Example: Device> enable Enables privileged EXEC mode. Enter your password, if prompted. Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 ip ssh server algorithm authentication {publickey | keyboard | password} Example: Device(config)# ip ssh server algorithm authentication publickey Defines the order of user authentication algorithms. Only the configured algorithm is negotiated with the secure shell (SSH) client.

Note • The SSH server must have at least one configured user authentication algorithm. • To use the certificate method for user authentication, the publickey keyword must be configured. • The ip ssh server algorithm authentication command replaces the ip ssh server authenticate user command. Step 4 ip ssh server algorithm publickey {x509v3-ssh-rsa [ssh-rsa] | ssh-rsa [x509v3-ssh-rsa]} Example: Device(config)# ip ssh server algorithm publickey x509v3-ssh-rsa Defines the order of public key algorithms. Only the configured algorithm is accepted by the SSH client for user authentication. Note The SSH client must have at least one configured public key algorithm: • ssh-rsa:

public-key-based authentication • x509v3-ssh-rsa: certificate-based authentication Step 5 ip ssh server certificate profile Example: Device(config)# ip ssh server certificate profile Configures server certificate profile and user certificate profile and enters SSH certificate profile configuration mode. Step 6 user Example: Device(ssh-server-cert-profile)# user Configures user certificate profile and enters SSH server certificate profile user configuration mode. X.509v3 Certificates for SSH Authentication 4

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