sh py lib. call ssh-keygen

To generate SSH keys using Python, you can utilize various libraries that interface with the ssh-keygen command or provide similar functionality in Python. This detailed guide outlines how to do so, including examples and explanations of the libraries you can use.

Generating SSH Keys in Python

Generating SSH keys can be achieved using a few different approaches within Python. Below, we will explore the usage of subprocess for calling ssh-keygen and the cryptography library for a more Pythonic solution.

Method 1: Using subprocess to Call ssh-keygen

The simplest way to generate an SSH key pair is to utilize the existing ssh-keygen tool available on your system through Python's subprocess module.

import subprocess

def generate_key(key_type='rsa', key_size=2048, key_path='~/.ssh/id_rsa'):
    # Expand user home directory
    key_path = os.path.expanduser(key_path)
    command = [
        'ssh-keygen',
        '-t', key_type,
        '-b', str(key_size),
        '-f', key_path,
        '-N', ''  # Empty passphrase
    ]
    
    try:
        subprocess.run(command, check=True)
        print(f"SSH key generated at: {key_path}")
    except subprocess.CalledProcessError as e:
        print(f"An error occurred: {e}")

generate_key()

This example generates an RSA key of 2048 bits and saves it to the default path. The -N flag specifies that no passphrase is used.

Method 2: Using the cryptography Library

If you prefer to generate keys programmatically without relying on external commands, the cryptography library is an excellent choice.

Installation

First, you need to install the library:

pip install cryptography

Key Generation Example

Here's a sample code snippet using the cryptography library:

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

def generate_ssh_key(rsa_key_size=2048, key_path='~/.ssh/id_rsa'):
    # Generate a private key
    private_key = rsa.generate_private_key(
        public_exponent=65537,
        key_size=rsa_key_size,
        backend=default_backend()
    )
    
    # Serialize the private key
    with open(os.path.expanduser(key_path), 'wb') as f:
        f.write(private_key.private_bytes(
            encoding=serialization.Encoding.PEM,
            format=serialization.PrivateFormat.TraditionalOpenSSL,
            encryption_algorithm=serialization.NoEncryption()
        ))
    
    # Generate the public key
    public_key = private_key.public_key()
    with open(os.path.expanduser(f"{key_path}.pub"), 'wb') as f:
        f.write(public_key.public_bytes(
            encoding=serialization.Encoding.OpenSSH,
            format=serialization.PublicFormat.OpenSSH
        ))
    
    print(f"SSH keys generated at: {key_path} and {key_path}.pub")

generate_ssh_key()

This function creates a private and public SSH key pair and saves them to the specified paths.

Best Practices

• Key Type: Use stronger key types such as ed25519, or if using RSA, go for at least 2048 bits.
• Passphrase: Always consider using a passphrase for added security, especially for private keys.
• File Permissions: Set appropriate permissions on your key files (e.g., chmod 600 id_rsa).

Conclusion

Incorporating SSH key generation within your Python scripts can enhance automation and security in various applications. By using the subprocess module for direct calls to ssh-keygen or utilizing the cryptography library for a fully contained Python approach, you can easily adapt the key generation process to your needs. Choose the method that best fits your development environment and security requirements.

For more information, check out the original tutorials on generating SSH keys with Stack Overflow and DEV Community.