SCP and SFTP

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Revision as of 18:53, 15 March 2011 by Sironitomas (Talk | contribs) (FTP over SSH)

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Introduction

SFTP refers to various forms of (more or less) secure file transfer protocols. This article lists two examples and how to set them up.

SSH file transfer protocol

SSH file transfer protocol is a FTP-like protocol that allows secure file transfer and manipulation, encrypting both passwords and transfered data.

Setting up SSH file transfer protocol with OpenSSH

To set-up SFTP you only need to install and configure OpenSSH. Once you have this running SFTP is running too, the default configuration file enables it. Follow the instructions below for older configs.

1. Open /etc/ssh/sshd_config with your favorite editor and add this line:

Subsystem sftp /usr/lib/ssh/sftp-server

2. Restart the SSH-daemon with:

# /etc/rc.d/sshd restart

And it should work. You can access your files with the sftp program or sshfs. Many standard ftp programs should work as well.

FTP over SSH

FTP over SSH encrypts passwords unlike plain FTP. FTP over SSH is not really a true protocol, it's just SSH + FTP or TLS/SSL + FTP . Note that there are many ways to set this up. This is one of them.

This setup in particular (using pure-ftpd + TLS) encrypts usernames, passwords, commands and server replies, but does NOT encrypt the data channel. This also means that there is reduced performance cost on data transfer.

Setting up FTP with pure-ftpd

We will use pure-ftpd:

# pacman -Sy pure-ftpd openssh openssl

Then you can go ahead and edit the configuration file:

# vi /etc/pure-ftpd.conf

You can start and stop the pure-ftpd daemon by

# /etc/rc.d/pure-ftpd start
# /etc/rc.d/pure-ftpd stop
# /etc/rc.d/pure-ftpd restart

and you can set it to automatically start by adding it to the daemons list in /etc/rc.conf.

Set up Certicificates

Refer to http://download.pureftpd.org/pub/pure-ftpd/doc/README.TLS for more information. The short version is this:

1. Create a Self-Signed Certificate:

# mkdir -p /etc/ssl/private
# openssl req -x509 -nodes -newkey rsa:1024 -keyout \
 /etc/ssl/private/pure-ftpd.pem \
 -out /etc/ssl/private/pure-ftpd.pem

2. Make it private:

# chmod 600 /etc/ssl/private/*.pem

3. Be aware that using 1024 bits in some countries will get you the legal banhammer. Choose 512 or less if unsure.

Enable TLS

Towards the bottom of /etc/pure-ftpd.conf you should find a section for TLS. Uncomment and change the TLS setting to 1 (which enables both FTP and SFTP):

TLS             1

Now restart the pure-ftpd daemon and you should be able to login with sftp-enabled clients (e.g. FileZilla, SmartFTP). (Dont forget to use port 22.)