What Is SFTP (SSH File Transfer Protocol)?

• Early File Transfer Protocols: FTP and FTPS

  Early File Transfer Protocols: FTP and FTPS

  File Transfer Protocol (FTP)

  FTP is a simple protocol based on the client-server model whose only purpose is to transfer files. It uses two types of connections:

  • Contrul connection for command and response for communication between the server and the client
  • Data connection to transfer file data. Data connection exists between the beginning and the end of the control connection

  The FTP client first establishes a connection with the server. Depending on the configuration, you may or may not need authentication. Then, based on the request, the file transfer takes place. By default, FTP uses port 21 for control and port 20 for data connection.

  File Transfer Protocol Secure (FTPS)

  FTPS is the extended version of FTP with an added security focus. In simple words, FTPS is FTP that supports TLS/SSL. FTPS uses the same logic for file transfer at its core, i.e., the use of control and data connections. However, all communication between the server and the client happens through a secure channel. FTPS supports the use of passwords and digital certificates. Common ports used by FTPS are 21, 989, and 990. FTPS has grown in popularity, but there are some drawbacks:

  • It has an inconsistent directory site listing format
  • It can be challenging to use behind firewalls
  • Using multiple ports might open your organization to attacks
  • Some FTP servers don’t support TLS/SSL
• What Is SFTP?

  What Is SFTP?

  SFTP (SSH File Transfer Protocol, also known as Secure FTP) is a popular method for securely transferring files over remote systems. This protocol was designed as an extension of the Secure Shell Protocol (SSH) version 2.0 to enhance secure file transfer capabilities. SFTP supports file access, transfers, and management functionalities without command or data channels. Instead, the data and commands are encrypted and transferred in specially formatted binary packets via a single, secured connection using SSH.

  Ordinary FTP clients can’t be used with SFTP servers, as they require dedicated SFTP clients, which are programs using SSH to access, manage, and transfer files. The command line interface (CLI) in UNIX and macOS X hosts can be used as SFTP clients. There are also graphical FTP clients supporting secure transfers, such as Serv-U^® Managed File Transfer Server, making file transfer more convenient for system administrators and end users. File transfers using SFTP can happen between an SFTP client and an SFTP server or between two SFTP servers.
• What Is an SFTP Server?

  What Is an SFTP Server?

  SFTP is based on the client-server model. An SFTP server is a system for handling file transfers securely. An SFTP server is usually the endpoint on which files are stored. It also takes care of authentication, downloading, and uploading files. When you want to perform a file transfer, the client establishes a connection with the SFTP server. The server authenticates the client and then processes client requests.

  You can set up the SFTP server to use various mechanisms for authentication, such as passwords, SSH keys, LDAP authentication, OTPs, and biometrics.

  To sum it up, here are some important functions of an SFTP server:

  • Authenticating SFTP clients
  • Storing and maintaining SSH keys
  • Using SSH for secure file transfer
  • Executing client requests for file transfer
• How Security Works in SFTP

  How Security Works in SFTP

  An SFTP connection can be authenticated in a few different ways. Basic authentication requires a user ID and password from the SFTP client user to connect to the SFTP server. 

  SSH authentication uses SSH keys to authenticate SFTP connections instead of, or in combination with, a user ID and password. An SSH public key and private key pair are required in this case.

  Generate a key pair on your computer (SFTP client) and copy the public key to the SFTP server. When the server authenticates your connection to it, PuTTY generates a signature using your private key. The server, which has the matching public key, can verify this signature and authenticate your connection.

  Regardless if the SFTP server is hacked or spoofed, the attacker gains only one signature, not your private key or password. Because signatures cannot be reused, the attacker gains nothing.

  SFTP operates over SSH, making it inherently secure. Unlike FTP and FTPS, the encryption can’t be triggered or turned off using AUTH commands.

  Since SFTP uses SSH for connection, the SFTP port number is the same as the SSH port, 22.
• SSH2 vs. SSH1

  SSH2 vs. SSH1

  SSH2 and SSH1 are fundamentally different protocols, with SSH2 emerging as a significant improvement over SSH1 in security, functionality, and performance. SSH1, introduced in 1995, had several security flaws, such as weak encryption and a monolithic structure that was susceptible to various attacks.

  SSH2, developed a year later, revamped the architecture to a modular design, enhancing flexibility and security. It supports robust encryption methods like AES and 3DES. It also introduces various authentication methods beyond the basic password-based option, such as public key authentication and host-based authentication.

  Despite the superiority of SSH2, the continued relevance of understanding SSH versions lies in ensuring system compatibility and security compliance. Some legacy systems may still operate under SSH1, posing significant security risks. Transitioning these systems to SSH2 is crucial for maintaining the integrity and security of network communications.
• Benefits of Using SFTP Over Other Protocols

  Benefits of Using SFTP Over Other Protocols

  SFTP offers several advantages over other file transfer protocols like FTP, FTPS, and SCP, particularly in terms of security, functionality, and ease of use.

  • Enhanced Security: SFTP provides a secure channel with end-to-end encryption, ensuring that both credentials and data are protected during transmission. This is a significant improvement over FTP’s unencrypted data transfer.
  • Functionality: SFTP offers extensive file management capabilities beyond simple file transfers. Users can access, modify, and manage files directly on the remote server, offering more versatility than SCP.
  • Compliance and Audit-Readiness: SFTP logs all file access and transfers, which is essential for compliance with regulations like HIPAA or GDPR. This traceability is critical for audit purposes.
  • Reliability: SFTP supports interrupted transfer resumption, file integrity checks post-transfer, and efficient handling of large files, enhancing the reliability and performance of data transfers.
  • Cross-Platform Compatibility: SFTP is supported across various operating systems, including Windows, Linux, and macOS. As a result, it is highly adaptable to diverse IT environments.
• What is the Difference Between SFTP vs. FTP?

  What is the Difference Between SFTP vs. FTP?

  SFTP (Secure File Transfer Protocol) and FTP (File Transfer Protocol) differ primarily in security and functionality. SFTP encrypts both commands and data. This encryption helps ensure information is secure throughout the data transfer, making it ideal for environments where data security is paramount. SFTP operates over a single, secure connection via the SSH protocol, typically on port 22. This simplifies firewall configurations and enhances security.

  FTP, however, transfers data in plain text and uses two separate channels for commands and data, which can expose it to security risks. This method may allow faster data transfer rates due to the lack of encryption but at the expense of security.

  Furthermore, SFTP offers comprehensive file management capabilities, allowing users to perform secure file operations over the connection. Since FTP lacks these features, SFTP is a more versatile and efficient option, especially for complex file management tasks.
• What is the Difference Between SFTP vs. FTPS?

  What is the Difference Between SFTP vs. FTPS?

  SFTP (Secure File Transfer Protocol) and FTPS (FTP Secure) both enhance the security of file transfers but differ in their mechanisms and implementations. SFTP is part of the SSH protocol suite, which provides a secure channel over a single connection, encrypting both commands and data. This makes it highly secure and simplifies firewall configurations, as it typically operates over one port (22).

  FTPS adds SSL or TLS encryption to the existing FTP protocol, which helps secure data channels. It operates in two modes: explicit, which secures connections on demand, and implicit, which secures connections from the start. However, FTPS uses two separate channels (command and data), often requiring additional firewall configuration due to its use of multiple ports (21 for commands and 20 for data).

  In terms of functionality, SFTP offers extensive file management capabilities beyond mere file transfer, such as directory listings and file manipulation within its secure session. FTPS focuses more on enhancing FTP with encryption and does not natively support such extensive file management features.
• Best Practices for SFTP Usage

  Best Practices for SFTP Usage

  • Strengthen Authentication: Prioritize key-based authentication over passwords to enhance security. Manage these keys effectively with expiration policies and secure storage solutions.
  • Maintain Software Integrity: Regularly update your SFTP server with the latest security patches to defend against new threats. This routine maintenance helps mitigate vulnerabilities and keep the server secure.
  • Restrict User Access: Apply the principle of least privilege by limiting user permissions to the bare minimum required for their tasks. This approach helps in minimizing potential internal and external risks.
  • Secure Network Communications: Ensure that your SFTP server uses strong encryption methods like AES and configure it to decline connections using outdated protocols. This step is crucial in safeguarding data from interception and tampering.
  • Monitor and Audit: Continuously monitor SFTP activities and maintain detailed logs of all transactions, including file transfers and access attempts. This practice aids in quick anomaly detection and compliance with security standards.
  • Enhance Network Security: Protect your network with adequate firewalls and consider setting up intrusion detection systems to monitor and alert to suspicious activities.
• Setting up an SFTP Server and Client

  Setting up an SFTP Server and Client

  In the example below, we’ll use two Linux machines, one of which acts as an SFTP server and the other as an SFTP client. Then we’ll set up the SFTP server and download files from the server to the client.

  First, set up an SFTP server. To download files from the SFTP server, you need a user that has access to communicate with the server via SFTP. So, create a user and add this user to a group. In this example, we’ll create a group called sftp_group and a user called sftp_user.

  sudo addgroup sftp_group
  sudo useradd -m sftp_user -g sftp_group

  Now add a password for this user and provide permissions to access a directory.

  sudo passwd sftp_user
  sudo chmod 700 /home/sftp_user/

  Now the user is ready, and the next step is to install the SSH daemon. To do this, open the terminal and run the command below:

  sudo apt install ssh

  For SFTP to work, you must change some configurations on the SFTP server.

  Open the /etc/ssh/sshd_config file using your favorite text editor and append the following lines to it:

  Match group sftp_group
  ChrootDirectory /home
  X11Forwarding no
  AllowTcpForwarding no
  ForceCommand internal-sftp

  This configuration lets users in the sftp_group access their home directories using the SFTP protocol. For the updated configuration to take effect, you need to restart the SSH service.

  sudo systemctl restart ssh

  You previously learned 22 is the default SFTP port as SFTP uses SSH, so check to see if this port is open:

  cat /etc/services | less

  Since we want to download a file using SFTP, switch to sftp_user and create a file.

  su – sftp_user

  You can use the whoami command to confirm the user switch has happened and then the ls command after creating a file to verify the file creation.

  Log out as this user by running “exit” on the terminal and use SFTP to download the file. First, you need to log in:

  sftp sftp_user@127.0.0.1

  As you’re accessing from the same machine, use 127.0.0.1. Now you’ve successfully logged in and can download the file.

  ls
  cd sftp_user/
  get sftp_file.txt

  Once the above command executes, you can run “exit” to close the SFTP connection and check if the file was downloaded. This is how you can use SFTP to transfer files. We used the command line in this example, but the majority of users use FTP servers with a GUI for administrators, which allows comfortable and efficient management and configuration of the file transfer system.
• Top Features of Secure File Transfer Services for the Enterprise

  Top Features of Secure File Transfer Services for the Enterprise

  Secure file transfer services for enterprises prioritize features that ensure robust security, compliance with regulatory standards, efficient management, and scalability to handle large volumes of data transfers across diverse operating environments. A key feature of these services is comprehensive security. This includes end-to-end encryption, secure authentication methods like multi-factor authentication, and detailed access controls that regulate who can send and receive files.

  For regulatory compliance, top-tier services offer extensive logging and reporting capabilities that help organizations meet requirements set by standards such as GDPR, HIPAA, and PCI-DSS. These logs ensure that all data transfers are traceable and auditable, as they provide crucial documentation that can be reviewed during compliance audits.

  Efficient management is another critical aspect. That’s where features like automation tools that streamline the process of scheduling, monitoring, and managing transfers can help. These tools often include user-friendly interfaces that simplify setup and maintenance, making it easy for non-technical users to manage secure remote file transfers.

  Lastly, scalability and integration capabilities are essential for enterprises. The best secure file transfer solutions can handle increasing amounts of data without degradation in performance and can integrate seamlessly with existing IT infrastructures, including cloud storage solutions and enterprise applications. This integration facilitates smooth workflows and allows enterprises to expand their operations without significant overhauls to their data transfer methods.