Secure File Transfer with SFTP and Password Authentication

Secure file transfer is a crucial aspect of many automated processes, including data backups, log transfers, and more. One popular method for secure file transfer is using the Secure File Transfer Protocol (SFTP). However, when automating SFTP transfers, providing password authentication in a secure manner can be challenging. This tutorial will explore various methods to achieve secure file transfer with SFTP and password authentication.

Understanding the Challenge

When using SFTP from a script or automated process, you cannot interactively enter your password as you would during an interactive session. Therefore, you need alternative methods to provide the necessary credentials for authentication.

Method 1: Using SSHPass

SSHPass is a utility designed to provide passwords to SSH-based applications, including SFTP. You can install SSHPass on most Linux systems using their package managers (e.g., apt-get for Ubuntu/Debian or yum for CentOS/RHEL).

Here’s an example of how to use SSHPass with SFTP:

export SSHPASS=your_password_here
sshpass -e sftp -oBatchMode=no -b - user@remote_host <<!
   cd incoming
   put local_file.log
   bye
!

However, storing passwords in environment variables or using them directly on the command line is not recommended due to security concerns. A more secure approach is to store your password in a file and then use SSHPass with the -f option:

echo 'your_password_here' > ~/.passwd
chmod 0400 ~/.passwd

sshpass -f ~/.passwd -e sftp -oBatchMode=no -b - user@remote_host <<!
   cd incoming
   put local_file.log
   bye
!

Method 2: Using LFTP

LFTP is another tool that can be used for SFTP transfers. It offers a more straightforward way to specify passwords and has additional features such as mirroring directories.

Here’s an example of how to use LFTP with password authentication:

lftp sftp://user:password@host -e "put local_file.name; bye"

However, this method also exposes your password in the command line. A better approach is to set the LFTP_PASSWORD environment variable and then execute LFTP with the --env-password option:

export LFTP_PASSWORD="your_password_here"
lftp --env-password sftp://user@host -e "put local_file.name; bye"

# Destroy password after use
export LFTP_PASSWORD=""

Method 3: Using Expect

Expect is a program that can automate interactions with command-line tools, including SFTP. It’s useful for creating scripts that mimic user interaction.

Here’s an example of how to use Expect with SFTP:

#!/usr/bin/expect

spawn sftp user@host
expect "password:"
send "your_password_here\n"
expect "sftp>"
send "cd incoming\n"
expect "sftp>"
send "put local_file.log\n"
expect "sftp>"
send "exit\n"
interact

Method 4: Using CURL

While not as commonly used for SFTP transfers, CURL can also be employed with the --user option to specify credentials.

Here’s an example:

curl -k "sftp://host:port/path/to/remote_file" --user "user:password" -o local_file.name

Keep in mind that using passwords directly on the command line, as shown in these examples, is not recommended due to security risks.

Conclusion

Each method has its advantages and disadvantages. SSHPass and LFTP offer straightforward solutions but require additional tools. Expect provides a powerful way to automate SFTP interactions but requires scripting knowledge. CURL can be used for simple transfers but might not be the best choice for complex scenarios.

When choosing a method, consider your specific requirements, including security constraints and the complexity of the transfers you need to automate. Always prioritize secure practices, such as storing passwords securely and avoiding their exposure in scripts or command lines.