SSH Certificates and their Real-World Applications

The ongoing pandemic has pushed many organizations to direct their employees to work from home, necessitating a switch to a public cloud infrastructure. Naturally, this raises data security concerns, as companies worry about bad actors intercepting their secure communications. A popular authentication protocol is Secure Shell, or SSH, and in this article we are going to examine some of its real-world applications.

What is SSH?

SSH is a cryptographic protocol used to authenticate communication between servers over an unsecured network. SSH is generally used to access Unix-like operating systems, but it can also be used on Microsoft Windows. The standard TCP port for SSH is 22. SSH certificates are useful because they are easy to set up and maintain, use strong encryption, provide role-based access, and ensure certificate validity.

x.509 certificate management

How SSH Certificates Simplify and Secure Access

The traditional way to access servers:

  • Password-based authentication

Each user creates a password that corresponds with a username. The username and password combination is used to log into the server. The server validates the combination, and if correct, grants access.

  • SSH connection by public key authentication

An SSH key pair, consisting of public and private cryptographic keys, is generated in the client’s system. The public key is copied to the server, which the client is trying to connect to, while the private key is stored on the client’s computer. When a user tries to log in, the server checks for the public key, generates a random string, and encrypts it using that public key. The encrypted message can only be decrypted with the associated private key. The server sends this encrypted message to the client’s computer. The client computer decrypts it using the private key and sends a message back to the server. If the message is valid, the client is authenticated, and the connection is made.

  • SSH connection by certificate authentication:

If the Certificate Authority (CA) server does not already have host keys, they will be generated, allowing a certificate to be issued on the CA server. The certificate is sent to the client’s machine and the host key details are pasted in the known_host file for authentication. The CA server’s host key is copied to all required servers for user login, and SSH service is then restarted after modifying the sshd_config file. Using a certificate also makes it possible to limit the lifetime of host keys and revoke them periodically for extra security.

Certificates vs. Public Key Authentication 

When a Linux server is installed, a system administrator grants certain accounts a password for authentication, including giving sudo/root access for some users. Managing accounts locally works well when dealing with a small number of servers, but as companies grow, they try to integrate account management into centralized systems, such as LDAP or Kerberos. But that approach has its share of drawbacks too – if a central authentication management system goes down, all credentials could be lost. When users are unable to access their systems, administrators often provide them with root access to circumvent central management mechanisms – this frequently happens when servers are brought down for maintenance.

SSH Certificates and their Real-World Applications

To get around central management system failure, system administrators might implement public key authentication – copying public keys to all servers – which makes it extremely difficult to keep track of them. Having an unknown public key in a server authorized_keys is risky and definitely not scalable, as authorized_keys requires defining trust by an individual key pair. This is where the certificate comes in. Authentication with a signed certificate provides a single point of trust with no dependency on any third-party infrastructure, eliminating risks associated with public key authentication.

Applications of SSH Certificates in the Real World

SSH certificates are primarily used to make connections with a remote machine and to execute commands, but they also support tunneling, forwarding TCP ports, and X11 connections. Users can transfer files using the associated SSH file transfer (SFTP) or secure copy (SCP) protocols. SSH uses the client-server model. 

SSH Certificates in Cloud Computing

SSH plays an important role in cloud computing by solving connection problems and helping avoid security risks associated with exposing a cloud-based virtual machine directly to the Internet. An SSH tunnel can provide a secure path over the Internet through a firewall to a virtual machine.

SSH Certificates Applications in Development and Monitoring

  1. Setting up automatic (password-less) login to a remote server in the network
  2. Securing file transfer protocols
  3. Port forwarding and tunneling (not to be confused with a VPN, which routes packets between different networks, or bridges two broadcast domains into one)
  4. Helping chatbots log into a server without needing authentication for monitoring and generating performance reports
  5. Helping with password-less authentication for database connectivity
  6. For development on a mobile or embedded device that supports SSH
  7. SSH certificates enable authentication via programming and help in automating tasks like file transfers, executing commands in servers, server monitoring, and sending reports to configured users

How AppViewX Helps with SSH Certificate Management

AppViewX helps customers manage SSH keys and hosts, along with a variety of certificate operations, including creating certificates, pushing them to devices, renewing, regenerating, and revoking certificates, and more. With AppViewX’s visual workflow, SecOps teams can automate any certificate management task. In addition, AppViewX offers detailed reports on certificate status and alerts security engineers when certificates are no longer valid or are about to expire. AppViewX helps automate key and certificate lifecycle management end-to-end, and keeps enterprise networks secure at all times. 

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