What command will prevent all... plain text in a configuration file?

What command will prevent all unencrypted passwords from displaying in plain text in a configuration file?

(config)# enable password secret
(config)# enable secret Secret_Password
(config-line)# password secret
(config)# service password-encryption
(config)# enable secret Encrypted_Password

The correct command to prevent all unencrypted passwords from displaying in plain text in a configuration file is:

(config)# service password-encryption

Detailed Explanation:

In Cisco devices such as routers and switches, passwords are often used for various levels of access control, including console access, virtual terminal lines (vty), and privileged mode. Without any additional configuration, these passwords can be stored in plain text in the device’s configuration file, which can pose a serious security risk. To mitigate this, Cisco offers the service password-encryption command, which ensures that passwords stored in the configuration file are encrypted.

Let’s break down how this command works, why it’s important, and its limitations.

1. Understanding the Purpose of Password Encryption

When configuring a Cisco device, several types of passwords are required to secure access:

Console Password: This controls access to the device through the console port.
VTY (Virtual Terminal Lines) Password: This controls remote access via protocols like Telnet or SSH.
Privileged Mode Passwords: This includes passwords that control access to privileged (enable) mode.

By default, these passwords can be visible in plain text when the configuration file is viewed using commands like show running-config. This visibility allows anyone with access to the configuration to easily read the passwords, increasing the risk of unauthorized access if the file is leaked or accessed by an unauthorized individual.

2. The Role of `service password-encryption`

The service password-encryption command solves this problem by automatically encrypting passwords in the configuration file. Once this command is enabled, any new password configured on the device will be stored in an encrypted format. If passwords already exist in the configuration when this command is entered, they will also be encrypted.

Here’s what happens under the hood:

Type 7 Encryption: The service password-encryption command applies Cisco’s weak encryption, commonly known as Type 7 encryption, to the passwords. This encryption is relatively basic and is reversible (meaning that someone with the right tools can decrypt it), but it serves as a basic deterrent to casual observers.
The encrypted password is stored in the configuration file in a form that looks something like this: 7 14141B180F0D.
When the show running-config command is issued, instead of displaying the actual password, the encrypted version is shown.

For example, after applying the service password-encryption command, a password like myPassword123 would be stored as something similar to 7 15171B5D2A.

3. Configuration and Usage

To apply the service password-encryption command, follow these steps:

Step 1: Enter Global Configuration Mode

Router# configure terminal

Step 2: Apply the `service password-encryption` Command

Router(config)# service password-encryption

Once applied, any password configured in the device will be encrypted. This includes passwords for console access, virtual terminal lines (vty), and the enable password.

Step 3: Verify the Encryption

To verify that passwords are encrypted, you can view the running configuration:

Router# show running-config

Instead of seeing plain text passwords, you’ll see encrypted values represented as Type 7.

4. Where This Command Is Applied

The service password-encryption command encrypts passwords used in various parts of the configuration, including:

Console Passwords:
```
(config)# line console 0
(config-line)# password myConsolePassword
```
With service password-encryption enabled, the password myConsolePassword would be stored in an encrypted format.
VTY Passwords:
```
(config)# line vty 0 4
(config-line)# password myVTYPassword
```
Similarly, the VTY password will be encrypted in the configuration file.
Enable Password: Although not directly related to service password-encryption, the enable password (configured with enable password) will also be encrypted when the service password-encryption is turned on.

5. Benefits of `service password-encryption`

Basic Security: While Type 7 encryption is not extremely strong, it does provide a layer of obfuscation that protects against casual exposure of passwords. Without encryption, anyone who can access the configuration file could easily read the passwords in plain text.
Deterrence: It deters unauthorized personnel who may have access to configuration files or backups from obtaining the passwords. Even though Type 7 encryption is weak, it requires extra effort to decrypt.
Best Practice: In most secure environments, implementing password encryption—even weak encryption—is considered a best practice to reduce the risk of exposure.
Compliance: For organizations adhering to security standards and best practices, the use of password encryption on network devices may be a requirement. Using the service password-encryption command helps meet such compliance needs.

6. Limitations of `service password-encryption`

Despite the benefits, there are some limitations and caveats that come with the service password-encryption command:

Weak Encryption (Type 7): The encryption used by the service password-encryption command is Type 7, which is known to be weak and reversible. Specialized tools or scripts can easily decrypt Type 7 passwords. This encryption should not be relied upon for high-security environments where password confidentiality is critical.
Only for Plain Text Passwords: This command only applies to passwords that are stored in plain text. It does not affect other types of passwords, such as those configured using the enable secret command, which uses much stronger MD5 hashing (Type 5 encryption). Therefore, it is highly recommended to use enable secret for privileged mode access instead of enable password, as it provides stronger security.
Not a Replacement for Strong Security Practices: Using service password-encryption alone does not guarantee high security. It is essential to combine this command with other security best practices, such as using strong, complex passwords, enabling AAA (Authentication, Authorization, and Accounting) mechanisms, and implementing access control lists (ACLs).

7. Alternatives for Enhanced Security

For environments where stronger password protection is necessary, the service password-encryption command should be complemented with stronger authentication methods. Cisco devices offer several alternatives:

Enable Secret: Instead of using the enable password command, use the enable secret command. The enable secret command uses MD5 hashing (Type 5), which is much more secure than Type 7 encryption. This hashed password cannot be easily reversed.
```
(config)# enable secret Secret_Password
```
AAA Authentication: For centralized authentication, consider using AAA (Authentication, Authorization, and Accounting) with a server like RADIUS or TACACS+.
SSH over Telnet: Use SSH for remote access instead of Telnet, as SSH provides encrypted communication, whereas Telnet sends data, including passwords, in plain text.

8. Conclusion

The service password-encryption command is an essential tool for improving the security of Cisco device configurations. While it uses weak Type 7 encryption, it provides a basic level of security by hiding plain text passwords in configuration files. However, it is crucial to recognize its limitations and complement it with stronger security practices, such as using enable secret, enabling SSH for remote access, and implementing AAA mechanisms for centralized authentication. In environments where security is paramount, relying solely on service password-encryption is insufficient.