Secure Shell (SSH) is a widely used protocol for secure communication between remote computers. System administrators and developers commonly use it to access servers, transfer files, and execute remote commands. One of the critical security features of SSH is using public key cryptography to authenticate the user and encrypt the data transmitted over the network. However, this security mechanism is only effective when SSH Keys are periodically changed. In this blog post, we will explore the importance of rotating SSH keys and discuss best practices for key management.
What are SSH Keys?
SSH keys authenticate users and encrypt data transmitted between two computers using the SSH protocol. SSH keys come in two parts: public and private keys. The public key is shared with the remote computer, while the private key is kept secret and used to encrypt data sent to the remote computer. When the remote computer receives data encrypted with the public key, it uses the corresponding private key to decrypt data and authenticates the user.
The public key is typically stored on the remote computer in a file called authorized_keys, whilst the user holds the private key on their local computer. The private key should be kept secure and not shared with anyone, as it gives the user access to the remote computer.
Why Rotate Keys?
SSH keys are essential for secure communication over the network, but they are not infallible. If an attacker gains access to an SSH key, they can use it to impersonate the user and gain unauthorized access to the remote computer. The rotation of keys helps mitigate this risk by ensuring an attacker cannot use a compromised key after a fixed period.
Key rotation involves generating a new key pair and replacing the old one on local and remote computers. By rotating SSH keys, organizations can limit the risk of compromising an old key and prevent unauthorized access to the network.
Best Practices for Key Rotation
Now that we understand the importance of rotating SSH keys let’s discuss best practices for key rotation.
1. Use a Key Rotation Schedule
The first step in establishing a key rotation policy is creating a schedule for rotating keys. The frequency of key rotation will depend on the organization’s security requirements and the risk associated with each key. Rotating keys at least once a year is recommended, but high-risk keys may need more frequent rotation.
2. Generate Strong Keys
When generating new keys, it is essential to use robust encryption algorithms and key lengths. The most commonly used algorithm for SSH keys is RSA, which provides strong encryption and is widely supported. NIST recommends using a key length of at least 2048 bits when generating RSA keys.
Organizations can use elliptic curve cryptography (ECC) keys for even stronger encryption, which provides equivalent security with smaller key sizes. SSH now supports Ed25519 and Ed448 keys, providing similar strength cryptography and faster performance.
3. Securely Distribute New Keys
The user must securely distribute new keys to the appropriate systems, add the new public key to the authorized_keys file on the remote computer, and encrypt the new private key safely on their local computer. It is essential to use secure channels for distributing keys, such as encrypted email or a secure file transfer protocol (SFTP).
4. Retire Old Keys
At the same time, the old keys should be retired to prevent unauthorized access to the network by removing the old public key from the authorized_keys file on the remote computer and the old private key from the user’s local computer.
5. Monitor Key Usage
Finally, it is essential to monitor key usage to detect any unauthorized access to the network by monitoring SSH logs or using specialized monitoring tools. The compromised key should be immediately retired and replaced with a new key pair if suspicious activity is detected.
Benefits of Rotating SSH Keys
Rotating SSH keys offers several benefits to organizations, including:
1. Improved Security
Rotating keys ensures that any compromised keys are retired and replaced with new, secure keys. By rotating SSH keys, organizations can limit the risk of compromising an old key and prevent unauthorized access to the network. If an attacker gains access to an old key, they can use it to impersonate the user and gain access to sensitive data or systems.
2. Compliance with regulations
Many industry regulations, such as the Payment Card Industry Data Security Standard (PCI DSS) and the Health Insurance Portability and Accountability Act (HIPAA), require organizations to implement strong security controls, including rotating cryptographic keys. By rotating SSH keys, organizations can ensure compliance with these regulations and avoid costly fines or penalties.
3. Mitigation of Human Error
SSH keys are often managed by system administrators or developers, who may inadvertently expose or share them with unauthorized users. By rotating keys regularly, organizations can mitigate the risk of human error and ensure that only authorized users have access to the network.
4. Better Accountability
Rotating SSH keys can also improve accountability by ensuring users have a unique key pair associated with their account. Unique keys allow organizations to track user activity and audit logs to detect unauthorized access or suspicious activity.
Conclusion
Rotating SSH keys is an essential security practice for organizations that use the SSH protocol to communicate over the network. By rotating keys regularly, organizations can limit the risk of compromising an old key and prevent unauthorized access to the network. Key rotation also ensures compliance with industry regulations and mitigates the risk of human error. Organizations should establish a schedule to implement effective key rotation, generate strong keys, securely distribute new keys, retire old keys, and monitor key usage. By following these best practices, organizations can ensure that their SSH keys are secure and their networks protected against unauthorized access.
SSH Key Management for Teams makes establishing a key rotation policy easy and implements the best practices described in this post. With the user-centric approach to key management and tools like our Desktop SSH Agent, the whole process of SSH key rotation can be automated, creating an effective policy without changing user practices.