SSH Algorithms for Common Criteria Certification

Restriction for SSH Algorithms for Common Criteria Certification

Starting from Cisco IOS XE Amsterdam 17.1.1, SHA1 is not supported.

Information About SSH Algorithms for Common Criteria Certification

This section provides information about the Secure Shell (SSH) Algorithms for Common Criteria Certification, the Cisco IOS SSH Server Algorithms and Cisco IOS SSH Client Algorithms.

SSH Algorithms for Common Criteria Certification

A Secure Shell (SSH) configuration enables a Cisco IOS SSH server and client to authorize the negotiation of only those algorithms that are configured from the allowed list. If a remote party tries to negotiate using only those algorithms that are not part of the allowed list, the request is rejected and the session is not established.

Cisco IOS SSH Server Algorithms

Cisco IOS secure shell (SSH) servers support the encryption algorithms (Advanced Encryption Standard Counter Mode [AES-CTR], AES Cipher Block Chaining [AES-CBC], Triple Data Encryption Standard [3DES]) in the following order:

Supported Default Encryption Order:

  1. aes128-gcm

  2. aes256-gcm

  3. aes128-ctr

  4. aes192-ctr

  5. aes256-ctr

Supported Non-Default Encrytion Order:

  1. aes128-cbc

  2. aes192-cbc

  3. aes256-cbc

  4. 3des

Cisco IOS SSH clients support the Message Authentication Code (MAC) algorithms in the following order:

Supported Default HMAC order:

  1. hmac-sha2-256-etm

  2. hmac-sha2-512-etm

  3. hmac-sha2-256

  4. hmac-sha2-512

Cisco IOS SSH clients support only one host key algorithm and do not need a CLI configuration.

Supported Default Host Key order:

  1. x509v3-ssh-rsa

  2. rsa-sha2-512

  3. rsa-sha2-256

  4. ssh-rsa

Cisco IOS SSH Client Algorithms

Cisco IOS secure shell (SSH) clients support the encryption algorithms (Advanced Encryption Standard counter mode [AES-CTR], AES Cipher Block Chaining [AES-CBC], Triple Data Encryption Standard [3DES]) in the following order:

Supported Default Encryption Order:

  1. aes128-gcm

  2. aes256-gcm

  3. aes128-ctr

  4. aes192-ctr

  5. aes256-ctr

Supported Non-Default Encrytion Order:

  1. aes128-cbc

  2. aes192-cbc

  3. aes256-cbc

  4. 3des

Cisco IOS SSH clients support the Message Authentication Code (MAC) algorithms in the following order:

Supported Default HMAC order:

  1. hmac-sha2-256-etm

  2. hmac-sha2-512-etm

  3. hmac-sha2-256

  4. hmac-sha2-512

Cisco IOS SSH clients support only one host key algorithm and do not need a CLI configuration.

Supported Default Host Key order:

  1. x509v3-ssh-rsa

  2. rsa-sha2-512

  3. rsa-sha2-256

  4. ssh-rsa

How to Configure SSH Algorithms for Common Criteria Certification

This section provides information on how to configure and troubleshoot:

  • Encryption key algorithm for a Cisco IOS SSH server and client

  • MAC algorithm for a Cisco IOS SSH server and client

  • Host Key algorithm for a Cisco IOS SSH server

Configuring an Encryption Key Algorithm for a Cisco IOS SSH Server and Client

Procedure

  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 | client} algorithm encryption {aes128-gcm | aes256-gcm | aes128-ctr | aes192-ctr | aes256-ctr | aes128cbc | aes192-cbs | 3des}

Example:

Device(config)# ip ssh server algorithm encryption aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des

Device(config)# ip ssh client algorithm encryption aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des

Defines the order of encryption algorithms in the SSH server and client. This order is presented during algorithm negotiation.

Note

 

The Cisco IOS SSH server and client must have at least one configured encryption algorithm.

Note

 

To disable one algorithm from the previously configured algorithm list, use the no form of this command. To disable more than one algorithm, use the no form of this command multiple times with different algorithm names.

Note

 
For a default configuration, use the default form of this command as shown below: 


Device(config)# ip ssh server algorithm encryption aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des

Step 4

end

Example:


Device(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Troubleshooting Tips

If you try to disable the last encryption algorithm in the configuration, the following message is displayed and the command is rejected: 


% SSH command rejected: All encryption algorithms cannot be disabled

Configuring a MAC Algorithm for a Cisco IOS SSH Server and Client

Procedure

  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 | client} algorithm mac {hmac-sha2-256-etm | hmac-sha2-512-etm | hmac-sha2-256 | hmac-sha2-512 }

Example:


Device(config)# ip ssh server algorithm mac hmac-sha2-256-etm hmac-sha2-512-etm hmac-sha2-256 hmac-sha2-512


Device(config)# ip ssh client algorithm mac hmac-sha2-256-etm hmac-sha2-512-etm hmac-sha2-256 hmac-sha2-512

Defines the order of MAC (Message Authentication Code) algorithms in the SSH server and client. This order is presented during algorithm negotiation.

Note

 

The Cisco IOS SSH server and client must have at least one configured Hashed Message Authentication Code (HMAC) algorithm.

Note

 

To disable one algorithm from the previously configured algorithm list, use the no form of this command. To disable more than one algorithm, use the no form of this command multiple times with different algorithm names.

Note

 
For default configuration, use the default form of this command as shown below: 


Device(config)# ip ssh server algorithm mac hmac-sha2-256-etm hmac-sha2-512-etm hmac-sha2-256 hmac-sha2-512

Step 4

end

Example:


Device(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Troubleshooting Tips

If you try to disable the last MAC algorithm in the configuration, the following message is displayed and the command is rejected: 


% SSH command rejected: All mac algorithms cannot be disabled

Configuring a Host Key Algorithm for a Cisco IOS SSH Server

Procedure

  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 hostkey {x509v3-ssh-rsa |rsa-sha2-512| rsa-sha2-256ssh-rsa}

Example:


Device(config)# ip ssh server algorithm hostkey x509v3-ssh-rsa rsa-sha2-512 rsa-sha2-256 ssh-rsa

Defines the order of host key algorithms. Only the configured algorithm is negotiated with the Cisco IOS secure shell (SSH) client.

Note

 

The Cisco IOS SSH server must have at least one configured host key algorithm:

  • x509v3-ssh-rsa—X.509v3 certificate-based authentication

  • ssh-rsa—Public-key-based authentication

Note

 

To disable one algorithm from the previously configured algorithm list, use the no form of this command. To disable more than one algorithm, use the no form of this command multiple times with different algorithm names.

Note

 
For default configuration, use the default form of this command as shown below: 


Device(config)# ip ssh server algorithm hostkey x509v3-ssh-rsa rsa-sha2-512 rsa-sha2-256 ssh-rsa

Step 4

end

Example:


Device(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Troubleshooting Tips

If you try to disable the last host key algorithm in the configuration, the following message is displayed and the command is rejected: 


% SSH command rejected: All hostkey algorithms cannot be disabled

Configuration Examples For SSH Algorithms for Common Criteria Certification

This section provides configuration examples for SSH algorithms for common certification.

Example: Configuring Encryption Key Algorithms for a Cisco IOS SSH Server


Device> enable
Device# configure terminal
Device(config)# ip ssh server algorithm encryption aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des

Device(config)# end

Example: Configuring Encryption Key Algorithms for a Cisco IOS SSH Client


Device> enable
Device# configure terminal
Device(config)# ip ssh client algorithm encryption aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des

Device(config)# end

Example: Configuring MAC Algorithms for a Cisco IOS SSH Server


Device> enable
Device# configure terminal
Device(config)# ip ssh server algorithm mac hmac-sha2-256-etm hmac-sha2-512-etm hmac-sha2-256 hmac-sha2-512
Device(config)# end

Example: Configuring Host Key Algorithms for a Cisco IOS SSH Server

Device> enable
Device# configure terminal
Device(config)# ip ssh server algorithm hostkey x509v3-ssh-rsa rsa-sha2-512 rsa-sha2-256 ssh-rsaa
Device(config)# end

Verifying SSH Algorithms for Common Criteria Certification

Procedure

Step 1

enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Example:


Device> enable

Step 2

show ip ssh

Displays configured Secure Shell (SSH) encryption, host key, and Message Authentication Code (MAC) algorithms.

Example:

The following sample output from the show ip ssh command shows the encryption algorithms configured in the default order: 

Device# show ip ssh

Encryption Algorithms: aes128-gcm aes256-gcm aes128-ctr aes192-ctr aes256-ctr aes128-cbc aes192-cbc aes256-cbc 3des
The following sample output from the show ip ssh command shows the MAC algorithms configured in the default order: 

Device# show ip ssh

MAC Algorithms: hmac-sha2-256-etm, hmac-sha2-512-etm,hmac-sha2-256,hmac-sha2-512
The following sample output from the show ip ssh command shows the host key algorithms configured in the default order: 

Device# show ip ssh

Hostkey Algorithms: x509v3-ssh-rsa, rsa-sha2-512, rsa-sha2-256,ssh-rsa

Feature Information for Secure Shell Algorithms for Common Criteria Certification

This table provides release and related information for features explained in this module.

These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise.

Release

Feature

Feature Information

Cisco IOS XE Everest 16.5.1a

Secure Shell Algorithms for Common Criteria Certification

The SSH Algorithms for Common Criteria Certification feature provides the list and order of the algorithms that are allowed for Common Criteria Certification. This module describes how to configure the encryption, Message Authentication Code (MAC), and host key algorithms for a secure shell (SSH) server and client so that SSH connections can be limited on the basis of the allowed algorithms list.

Use Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.