What is Passphrase? It Should Be Hard to Guess Protecting a Private Key Protecting SSH keys PGP / GPG Private Key Protection A passphrase is similar to a password. However, a password generally refers to something used to authenticate or log into a system. A passphrase generally refers to a secret used to protect an encryption key. Commonly, an actual encryption key is derived from the passphrase and used to encrypt the protected resource. A good passphrase should have at least 15, preferably 20 characters and be difficult to guess. It should contain upper case letters, lower case letters, digits, and preferably at least one punctuation character. No part of it should be derivable from personal information about the user or his/her family. Sometimes there is a need to generate random passwords or phrases automatically. The purpose of the passphrase is usually to encrypt the private key. This makes the key file by itself useless to an attacker. It is not uncommon for files to leak from backups or decommissioned hardware, and hackers commonly exfiltrate files from compromised systems. To use an encrypted key, the passphrase is also needed. In a way, they are two separate factors of authentication. SSH keys are used for authenticating users in information systems. The SSH keys themselves are private keys; the private key is further encrypted using a symmetric encryption key derived from a passphrase. The key derivation is done using a hash function. Passphrases are commonly used for keys belonging to interactive users. Their use is strongly recommended to reduce risk of keys accidentally leaking from, e.g., backups or decommissioned disk drives. In practice, however, most SSH keys are without a passphrase. There is no human to type in something for keys used for automation. The passphrase would have to be hard-coded in a script or stored in some kind of vault, where it can be retrieved by a script. An attacker with sufficient privileges can easily fool such a system. Thus, there would be relatively little extra protection for automation. More than 90% of all SSH keys in most large enterprises are without a passphrase. However, this depends on the organization and its security policies. Use of proper SSH key management toolsis recommended to ensure proper access provisioning and termination processes, regularly changing keys, and regulatory compliance. SSH keys can be generated with tools such as ssh-keygen and PuTTYgen. These tools ask for a phrase to encrypt the generated key with. Private keys used in email encryption tools like PGP are also protected in a similar way. Such applications typically use private keys for digital signing and for decrypting email messages and files.Contents
What is Passphrase?
It Should Be Hard to Guess
Protecting a Private Key
Protecting SSH keys
PGP / GPG Private Key Protection
When it comes to passphrases, encryption, and key protection, I'm well-versed in the nuances and importance of securing sensitive data. Let's break down the concepts covered in the article:
Passphrase vs. Password:
A passphrase serves a similar function to a password but is primarily used to protect encryption keys rather than for system authentication. It's crucial to create robust passphrases that are longer (preferably 15-20 characters), include a mix of upper and lower case letters, digits, and even punctuation marks. Avoiding personal information in a passphrase is critical to prevent it from being guessed or hacked.
Protecting Private Keys:
Passphrases play a pivotal role in encrypting private keys, rendering the key file useless to attackers if obtained. It's common for files, including private keys, to leak from backups or decommissioned hardware. However, without the passphrase, the encrypted key remains inaccessible.
SSH Key Protection:
SSH keys, used for user authentication in information systems, involve encrypting the private key using a passphrase-derived symmetric encryption key. While passphrases add an extra layer of security, their implementation for automated processes is challenging. Most SSH keys used for automation lack passphrases due to the need for non-human interaction. However, this practice poses a risk, leaving keys vulnerable if accessed by an attacker with sufficient privileges.
Best Practices and Tools:
Proper SSH key management tools are recommended for secure access provisioning, regular key changes, and compliance. Tools like ssh-keygen and PuTTYgen facilitate the generation of SSH keys and prompt users to encrypt keys with a passphrase for added security.
PGP / GPG Key Protection:
Similar to SSH keys, private keys used in email encryption tools like PGP/GPG also rely on passphrase protection. These keys serve purposes like digital signing and decrypting email messages/files, emphasizing the need for strong passphrases to safeguard sensitive communications.
Understanding these concepts is pivotal for ensuring data security in various contexts where encryption keys play a crucial role in protecting sensitive information.
