Private and public key files

Private and public key files are fundamental components in asymmetric cryptography used for secure communication, authentication, and data integrity. In the context of SSH and other cryptographic applications, these keys work together to establish secure connections and verify identities. Here's a detailed overview:

Private Key Files

Purpose: The private key is a confidential key that should be kept secure. It is used to decrypt data that was encrypted with the corresponding public key, or to sign data, allowing others to verify the authenticity of the signed data using the public key.

Location: Private key files are usually stored in a secure directory with restricted permissions.

Common Locations:

  • SSH: /etc/ssh/, /home/username/.ssh/

  • GPG: ~/.gnupg/

  • TLS/SSL: /etc/ssl/private/

Permissions: The private key file should have restrictive permissions to ensure that only the owner (or root) can read or write the file. Typically, permissions are set to 600 (read/write for owner only).

Examples:

  • SSH: /etc/ssh/ssh_host_rsa_key, /home/username/.ssh/id_rsa

  • GPG: ~/.gnupg/private-keys-v1.d/

  • TLS/SSL: /etc/ssl/private/server.key

Example File Content (RSA Private Key):

-----BEGIN RSA PRIVATE KEY-----
MIIEpAIBAAKCAQEA7Q...
...
-----END RSA PRIVATE KEY-----

Public Key Files

Purpose: The public key is distributed openly and used to encrypt data that can only be decrypted by the corresponding private key. It is also used to verify signatures created with the private key.

Location: Public key files are often distributed or made accessible as part of public key infrastructure.

Common Locations:

  • SSH: /etc/ssh/, /home/username/.ssh/

  • GPG: ~/.gnupg/pubring.gpg

  • TLS/SSL: /etc/ssl/certs/

Permissions: Public key files are usually world-readable as they are meant to be shared.

Examples:

  • SSH: /etc/ssh/ssh_host_rsa_key.pub, /home/username/.ssh/id_rsa.pub

  • GPG: ~/.gnupg/pubring.kbx

  • TLS/SSL: /etc/ssl/certs/server.crt

Example File Content (RSA Public Key):

ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEArjG3Oj...

Key File Generation

SSH Example: To generate a new pair of SSH keys:

ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

This command generates two files:

  • Private Key: ~/.ssh/id_rsa

  • Public Key: ~/.ssh/id_rsa.pub

GPG Example: To generate a new GPG key pair:

gpg --full-generate-key

This command generates several files in the GPG keyring:

  • Private Key: ~/.gnupg/private-keys-v1.d/

  • Public Key: ~/.gnupg/pubring.kbx

TLS/SSL Example: To generate a new pair of TLS/SSL keys:

openssl genpkey -algorithm RSA -out server.key
openssl req -new -key server.key -out server.csr
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

This command generates:

  • Private Key: server.key

  • Public Key Certificate: server.crt

Key Security Best Practices

  1. Keep Private Keys Secret: Never share or expose private keys. Only public keys should be distributed.

  2. Use Strong Passphrases: If possible, protect private keys with a strong passphrase.

  3. Restrict Permissions: Ensure private key files have restrictive permissions (e.g., 600).

  4. Secure Storage: Store private keys in secure, access-controlled locations.

  5. Regular Key Rotation: Periodically replace and rotate keys to maintain security.

Summary

Private and public key files are crucial for various cryptographic functions, including secure communication and authentication. Proper management and protection of private keys, along with the distribution of public keys, are essential for maintaining security and trust in cryptographic systems.

PreviousPermitRootLogin, PubKeyAuthentication, AllowUsers, PasswordAuthentication, ProtocolNextSSLCACertificateFile, SSLCACertificatePath

Last updated