How Can I Verify Host Keys Securely When Using pysftp?

Verify Host Key with pysftp

When using pysftp to establish an SSH connection, it's essential to verify the server's host key against a trusted source to ensure secure communication. By default, pysftp attempts to load known host keys from the '~/.ssh/known_hosts' file. However, if the server's host key is stored in a different location, such as the registry used by PuTTY, it's crucial to reconcile this difference.

Options for Host Key Verification in pysftp

pysftp provides several options for managing host key verification:

• Load Host Keys from a File:

  • Specify the path to the known_hosts file using the cnopts.knownhosts attribute. This will load host keys from the specified file.

• Use Custom Host Keys:

  • Create a HostKeys object and add the expected host key using the add() method. This allows you to manually specify the host key to be verified.

• Disable Host Key Verification:

  • Set cnopts.hostkeys to None to disable host key verification. However, this is not recommended as it compromises security.

Recommended Approach

To maintain security and ensure proper host key verification, it's best to load known host keys from a trusted source. If the host keys are stored in the registry, consider using a tool like ssh-keyscan to retrieve the necessary information and store it in the appropriate format.

Example Code

Here's an example demonstrating the use of custom host keys:

import pysftp as sftp

cnopts = pysftp.CnOpts()
host_key = paramiko.RSAKey(data=b'YOUR_HOST_KEY')  # Replace with the server's host key
cnopts.hostkeys.add('my_server.com', 'ssh-rsa', host_key)

with sftp.Connection('my_server.com', username='root', password='*********', cnopts=cnopts) as sftp:
    # Perform file transfer operations, etc.

By carefully handling host key verification, you can establish secure SSH connections and prevent man-in-the-middle attacks.

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