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 encryptionalgorithms (Advanced Encryption Standard Counter Mode [AES-CTR], AES Cipher Block Chaining [AES-CBC], Triple Data Encryption Standard [3DES]), Galois/Counter Mode (GCM), Key Exchange (KEX), and Public Key in the following order:

Supported Default Encryption Order:

  1. chacha20-poly1305@openssh.com

  2. aes128-gcm@openssh.com

  3. aes256-gcm@openssh.com

  4. aes128-gcm

  5. aes256-gcm

  6. aes128-ctr

  7. aes192-ctr

  8. aes256-ctr

Supported Non-Default Encryption 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

  2. 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. ssh-rsa

Cisco IOS SSH servers support the Key Exchange (KEX) DH Group algorithms in the following default order:

  1. curve25519-sha256@libssh.org

  2. diffie-hellman-group14-sha1

  3. ecdh-sha2-nistp256

  4. ecdh-sha2-nistp384

  5. ecdh-sha2-nistp521

Cisco IOS SSH servers support the public key algorithms in the following default order:

  1. ecdsa-sha2-nistp256

  2. ecdsa-sha2-nistp384

  3. ecdsa-sha2-nistp521

  4. rsa-sha2-256

  5. rsa-sha2-512

  6. ssh-ed25519

  7. ssh-rsa

  8. x509v3-ecdsa-sha2-nistp256

  9. x509v3-ecdsa-sha2-nistp384

  10. x509v3-ecdsa-sha2-nistp521

  11. x509v3-ssh-rsa

  12. ssh-ed25519

Cisco IOS SSH Client Algorithms

Cisco IOS secure shell (SSH) clients support the theencryption algorithms (Advanced Encryption Standard counter mode [AES-CTR], AES Cipher Block Chaining [AES-CBC], Triple Data Encryption Standard [3DES]), Galois/Counter Mode (GCM), Key Exchange (KEX), and Public Key in the following order:

Supported Default Encryption Order:

  1. chacha20-poly1305@openssh.com

  2. aes128-gcm@openssh.com

  3. aes256-gcm@openssh.com

  4. aes128-gcm

  5. aes256-gcm

  6. aes128-ctr

  7. aes192-ctr

  8. aes256-ctr

Supported Non-Default Encryption 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

  2. 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. ssh-rsa

Cisco IOS SSH clients support the Key Exchange (KEX) DH Group algorithms in the following default order:

  1. curve25519-sha256@libssh.org

  2. diffie-hellman-group14-sha1

  3. ecdh-sha2-nistp256

  4. ecdh-sha2-nistp384

  5. ecdh-sha2-nistp521

Cisco IOS SSH clients support the public key algorithms in the following default order:

  1. ecdsa-sha2-nistp256

  2. ecdsa-sha2-nistp384

  3. ecdsa-sha2-nistp521

  4. rsa-sha2-256

  5. rsa-sha2-512

  6. ssh-ed25519

  7. ssh-rsa

  8. x509v3-ecdsa-sha2-nistp256

  9. x509v3-ecdsa-sha2-nistp384

  10. x509v3-ecdsa-sha2-nistp521

  11. x509v3-ssh-rsa

  12. ssh-ed25519

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 {3des-cbcaes128-cbcaes128-ctraes128-gcmaes128-gcm@openssh.comaes192-cbcaes192-ctraes256-cbcaes256-ctr aes256-gcmaes256-gcm@openssh.comchacha20-poly1305@openssh.com}

Example:

Device(config)# ip ssh server algorithm encryption 3des-cbc aes128-cbc aes128-ctr aes128-gcm aes128-gcm@openssh.com aes192-cbc aes192-ctr aes256-cbc aes256-ctr aes256-gcm aes256-gcm@openssh.com chacha20-poly1305@openssh.com
Device(config)# ip ssh client algorithm encryption 3des-cbc aes128-cbc aes128-ctr aes128-gcm aes128-gcm@openssh.com aes192-cbc aes192-ctr aes256-cbc aes256-ctr aes256-gcm aes256-gcm@openssh.com chacha20-poly1305@openssh.com

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.

  • 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.

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


Device(config)# ip ssh server algorithm encryption 3des-cbc aes128-cbc aes128-ctr aes128-gcm aes128-gcm@openssh.com aes192-cbc aes192-ctr aes256-cbc aes256-ctr aes256-
gcm aes256-gcm@openssh.com chacha20-poly1305@openssh.com

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.

  • 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.

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 Key Exchange DH Group Algorithm for 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 kex {curve25519-sha256@libssh.org | diffie-hellman-group14-sha1 | ecdh-sha2-nistp256 | ecdh-sha2-nistp384|ecdh-sha2-nistp521 }

Example:


Device(config)# ip ssh server algorithm kex curve25519-sha256@libssh.org diffie-hellman-group14-sha1 ecdh-sha2-nistp256 ecdh-sha2-nistp384 ecdh-sha2-nistp521


Device(config)# ip ssh client algorithm kex curve25519-sha256@libssh.org diffie-hellman-group14-sha1 ecdh-sha2-nistp256 ecdh-sha2-nistp384 ecdh-sha2-nistp521

Definesthe order of Key Exchange 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 KEX algorithm.

  • 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.

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


Device(config)# ip ssh server algorithm kex curve25519-sha256@libssh.org diffie-hellman-group14-sha1 ecdh-sha2-nistp256 ecdh-sha2-nistp384 ecdh-sha2-nistp521

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 KEX algorithm in the configuration, the following message is displayed and the command is rejected: 


% SSH command rejected: All KEX algorithms cannot be disabled

Configuring a Public 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 publickey {ecdsa-sha2-nistp256 | ecdsa-sha2-nistp384 | ecdsa-sha2-nistp521 | rsa-sha2-256 | rsa-sha2-512 | ssh-ed25519 | ssh-rsa | x509v3-ecdsa-sha2-nistp256 | x509v3-ecdsa-sha2-nistp384 | x509v3-ecdsa-sha2-nistp521 | x509v3-ssh-rsa | ssh-ed25519}

Example:


Device(config)# ip ssh server algorithm publickey ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521rsa-sha2-256 rsa-sha2-512 ssh-ed25519 ssh-rsa x509v3-ecdsa-sha2-nistp256 x509v3-ecdsa-sha2-nistp384 x509v3-ecdsa-sha2-nistp521 x509v3-ssh-rsa ssh-ed25519


Device(config)# ip ssh client algorithm publickey ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521rsa-sha2-256 rsa-sha2-512 ssh-ed25519 ssh-rsa x509v3-ecdsa-sha2-nistp256 x509v3-ecdsa-sha2-nistp384 x509v3-ecdsa-sha2-nistp521 x509v3-ssh-rsa ssh-ed25519

Defines the order of public key 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 public key algorithm.

  • 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.

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


Device(config)# ip ssh server algorithm publickey ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521rsa-sha2-256 rsa-sha2-512 ssh-ed25519 ssh-rsa x509v3-ecdsa-sha2-nistp256 x509v3-ecdsa-sha2-nistp384 x509v3-ecdsa-sha2-nistp521 x509v3-ssh-rsa ssh-ed25519

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 public key algorithm in the configuration, the following message is displayed and the command is rejected: 


% SSH command rejected: All public key 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

  • 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.

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 3des-cbc aes128-cbc aes128-ctr aes128-gcm aes128-gcm@openssh.com aes192-cbc aes192-ctr aes256-cbc aes256-ctr aes256-
gcm aes256-gcm@openssh.com chacha20-poly1305@openssh.com
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 3des-cbc aes128-cbc aes128-ctr aes128-gcm aes128-gcm@openssh.com aes192-cbc aes192-ctr aes256-cbc aes256-ctr aes256-
gcm aes256-gcm@openssh.com chacha20-poly1305@openssh.com
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 Key Exchange DH Group for a Cisco IOS SSH Server


Device> enable
Device# configure terminal
Device(config)# ip ssh server algorithm kex ecdh-sha2-nistp256 ecdh-sha2-nistp384 ecdh-sha2-nistp521 diffie-hellman-group14-sha1 curve25519-sha256@libssh.org
Device(config)# end

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

Device> enable
Device# configure terminal
Device(config)# ip ssh server algorithm publickey ecdsa-sha2-nistp256 ecdsa-sha2-nistp384 ecdsa-sha2-nistp521 rsa-sha2-256 rsa-sha2-512 ssh-ed25519 ssh-rsa x509v3-ecdsa-sha2-nistp256 x509v3-ecdsa-sha2-nistp384 x509v3-ecdsa-sha2-nistp521 x509v3-ssh-rsa ssh-ed25519
Device(config)# end

The following example shows how to return to the default behavior in which all public key algorithms are enabled in the predefined order: 

Device> enable
Device# configure terminal
Device(config)# default ip ssh server algorithm publickey
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-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, 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, ssh-rsa

Feature History for Secure Shell Algorithms for Common Criteria Certification

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

These features are available in all the 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.

Cisco IOS XE Cupertino 17.8.1

Secure Shell Encryption Algorithms

Cisco IOS SSH Server and Client support for the following encryption algorithms have been introduced:

  • aes128-gcm@openssh.com

  • aes256-gcm@openssh.com

  • chacha20-poly1305@openssh.com

Cisco IOS XE Cupertino 17.9.1

Secure Shell Encryption Algorithms

Cisco IOS SSH Server and Client support for the following encryption algorithms have been introduced:

  • aes128-gcm@openssh.com

  • aes256-gcm@openssh.com

Use the Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to https://cfnng.cisco.com/.