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How do I make a RSA key pair for a SSH connection? (RSA keys, 2048 bits.) Click Generate. Move your mouse to the appropriate area of the window as directed. How to delete the rsa key already created in ASDM using ASDM, asa code 9.1. Go to Solution. Hi,I was trying to 2fa cisco duo, all the required settings done as per below. Create Please login to create content. Related Content. $ ssh-keygen -t rsa -b 4096 -C 'youremail@example.com' This creates a new ssh key, using the provided email as a label. Generating public/private rsa key pair. When you're prompted to 'Enter a file in which to save the key,' press Enter. This accepts the default file location. To reset the RSA key pair, use the vManage Configuration Certificates screen. In the Controllers tab, select a device. Click the More Actions icon to the right of the row and click Reset RSA. Click OK to confirm resetting of the device's RSA key and to generate a new CSR with new public/private keys. Oct 16, 2019  An RSA key pair (a public and a private key) is required before you can obtain a certificate for your router; that is, the end host must generate a pair of RSA keys and exchange the public key with the certification authority (CA) to obtain a certificate and enroll in a PKI.

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.

SSH Encryption Algorithms

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.

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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.

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SSH Key Exchange

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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.

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. Sql auto generate primary key. 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

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.

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/key-generator-steam-no-survey.html. 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.

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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

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