1. Cisco Switch Can't Generate Crypto Key Rsa
2. Cisco Crypto Key Generate Rsa
3. Cisco Crypto Key Gen Rsa
4. Cisco Switch Crypto Key Generate Rsa
5. Cisco Crypto Key Generate Rsa Command For Ssh

How I create RSA key and enable SSH access in Cisco VG202, in a Cisco router I use the next commands(but in a VG not exists): conf t. Crypto key generate rsa modulus 1024 ip domain-name domain-name ip ssh version 2 ip ssh time-out 120 ip ssh authentication-retries 3 line vty 0 4 transport input telnet ssh end. How I create RSA key and enable SSH access in Cisco VG202, in a Cisco router I use the next commands(but in a VG not exists): conf t crypto key generate rsa modulus 1024 ip domain-name domain-name ip ssh version 2 ip ssh time-out 120 ip ssh authentication-retries 3 line vty 0 4 transport input telne. Config t crypto key generate rsa exit Then ssh to the router and complete the config. Or just enable telnet if you can get away with it. Config t vty 0 4 transport input ssh telnet exit I have a perl script that does this to reset enable passwords. Yes, it is necessary to generate the rsa key pair for SSH access. Here is the command to check the keypair in your ASA: show crypto key mypubkey rsa. Hope that helps. Crypto key generate rsa. cryptokeygeneratersa,page2 Cisco IOS Security Command Reference: Commands A to C, Cisco IOS XE Release 3SE (Catalyst 3850 Switches). Jun 11, 2019 SW1 ( config)# crypto key generate rsa. How many bits in the modulus 512: 1024% Generating 1024 bit RSA keys, keys will be non-exportableOK Set the size of key to 1024 bits. If your Cisco Switch is running an older version of Cisco IOS image, then it is extremely recommended that you upgrade to latest Cisco IOS.

Last year, I wrote a post about securing the Cisco IOS SSH server. It also makes sense to create one for Cisco ASA especially when my old post about enabling SSH on Cisco ASA was back in 2012. That blog post didn’t include the advanced configurations that will improve the security of the Cisco ASA SSH server. With this post, I’d like to share the minimum advanced SSH configurations that network engineers should consider adding to their ASA template.

Enabling Cisco ASA SSH server

Before we can connect to our Cisco ASA via SSH, we need to have a checklist of things we need to configure.

1. While it’s a good idea to have enable password configured, it is optional for SSH.
2. You must have at least one user account locally.
3. Configure ASA’s authentication method. The authentication method can be local, RADIUS, or TACACS+.
4. Generate RSA key pair.
5. Configure ACL to allow a specific IP address or range(s).

Setting enable password

My old post covered how to set enable password. It’s the same command on how to set the enable password, but in the newer ASA software, it uses PBKDF2 to encrypt the password compared to the MD5-based hash in older ASA software.

Generating RSA keys

As covered in my old post, to enable SSH on the ASA, we’ll need to generate RSA key pair first. Current NIST recommendation is to use 2048-bit or above. In this post, I am going to use 4096-bit key pair.

SSH Version

Configuring the Cisco ASA SSH server to accept only version 2 is best practice. The reason for this is because SSHv1 has vulnerabilities. That said, make sure to add this to your ASA template.

Cisco Switch Can't Generate Crypto Key Rsa

SSH Encryption Algorithms

Cisco Crypto Key Generate Rsa

By default, it seems that the ASA’s encryption algorithm is configured to use the medium settings. Unfortunately, I cannot seem to verify it using the show run all command. However, the combination of show ssh and show ssh ciphers does the trick.

The client and server negotiate the encryption algorithm. That said, it is possible that the client would pick a weaker cipher. To avoid that, we’re going to specify the use of a safer cipher. According to this thread, the use of EAX or GCM is preferable when available. If not, the use CTR over CBC mode. By specifying the encryption algorithm, we’re telling ASA to only offer the AES-256-CTR mode to any clients that try to connect to it.

Here’s the verbose output of my SSH to a Cisco ASA using the default SSH cipher encryption.

Let’s configure the ASA to only use AES256 CTR mode.

Here’s the verbose output of my SSH connection to a Cisco ASA device using the SSH cipher encryption configuration mentioned above.

SSH Integrity Algorithm

By default, it seems that the ASA’s integrity algorithm is configured to use the medium settings. Unfortunately, I cannot seem to verify it using the show run all command. However, the combination of show ssh and show ssh ciphers does the trick.

The default setting for the ASA SSH integrity algorithm is medium. Which means, it will accept both HMAC-SHA1 and HMAC-SHA1-96. The difference between the two algorithms is the digest length. The HMAC-SHA1-96 is a truncated message digest. From my limited understanding, the HMAC-SHA1-96 is the weakened version of HMAC-SHA1 due to the shortened message digest.

Here’s the verbose output of my SSH to a Cisco ASA using the default SSH integrity algorithm.

Let’s configure the ASA to only use HMAC-SHA1.

Here’s the verbose output of my SSH connection to a Cisco ASA device using the SSH integrity algorithm configuration mentioned above.

SSH Key Exchange

The ASA support two Diffie-Hellman key exchange methods and these are DH Group 1 (768-bit) and DH Group 14 (2048-bit). By default, the ASA is set to use Diffie-Hellman Group 1. Unfortunately, this is below what NIST recommends to use in this day and age.

Here’s a Cisco ASA with default SSH key exchange configuration. I issued the no ssh key-exchange to be sure.

Here’s the verbose output of my SSH connection to a Cisco ASA using the default SSH key exchange.

Let’s configure the ASA to use DH Group 14.

Keytool generate csr and key. Here’s the verbose output of my SSH connection to the Cisco ASA after changing the key exchange method.

SSH ACL

Restricting remote management to a certain IP address is a best practice. It is also required to add the ACL, or we won’t be able to access the Cisco ASA via SSH. That said, I included the command here.

Final Words

Cisco Crypto Key Gen Rsa

All of the configurations covered here are what I’d say minimum security standard for all Cisco ASA devices. It is, after all, a network security device, so it is a must to secure it properly. Though this post is just a small part of protecting the management plane and network engineers must incorporate other security configurations.

Are you ready to improve your network security?

Cisco Switch Crypto Key Generate Rsa

Let us answer more questions by contacting us. We’re here to listen and provide solutions that are right for you.

NetworkJutsu provides networking and network security consulting services for startups, a more established small and medium-sized business (SMB), or large business throughout the San Francisco Bay Area.

Cisco Crypto Key Generate Rsa Command For Ssh

Want to learn more about ASA?

Cisco ASA: All-in-one Next-Generation Firewall, IPS, and VPN Services (3rd Edition)
Cisco ASA for Accidental Administrators: An Illustrated Step-by-Step ASA Learning and Configuration Guide

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.