Updated September 29, 2023

Introduction to SFTP

Today’s digital landscape demands secure data communication. Secure File Transfer Protocol emerges as a critical option for protecting sensitive data in transit. In this article, we will delve into the complexities of SFTP, exploring its mechanisms, benefits, setup procedures, and real-world applications to comprehend its critical position in current cybersecurity.

Introduction to SFTP
What is SFTP?
How does it work?
How to Transfer File?
List of Common SFTP commands
Advantages
Disadvantages
Security Measures
Difference Between FTPs vs SFTP

What is SFTP?

Secure File Transfer Protocol is an encrypted and secure means of transmitting files between systems across a network. Unlike its predecessor, FTP (File Transfer Protocol), SFTP employs advanced security measures by utilizing encryption techniques to safeguard the integrity and confidentiality of data during transit. SFTP operates on a secure channel, usually through SSH (Secure Shell), which provides an underlying transport protocol. This combination ensures that critical information is protected from unauthorized access and eavesdropping while being transmitted between the client and server.

How does it work?

Secure File Transfer Protocol is designed to provide a secure and reliable way to transfer and manage files over a TCP/IP network. It builds upon the foundation of the SSH (Secure Shell) protocol to ensure data confidentiality, integrity, and authentication during the file transfer process. Let’s break down the key components and processes involved in how SFTP works:

Secure Data Transfer: SFTP is designed to address the security vulnerabilities of traditional FTP. It encrypts the transferred data, preventing unauthorized access and eavesdropping during transmission. Encrypting the data packets, the content remains indecipherable even if intercepted by unauthorized parties.
Similarities to FTP and Linux Shell Commands: SFTP uses commands similar to the standard FTP protocol. Many SFTP commands mirror common Linux shell commands, making them intuitive for users familiar with command-line interfaces. This allows users to perform tasks like listing directories, transferring files, creating directories, and managing files in a manner consistent with their experience on Linux systems.
Tasks and Capabilities: SFTP serves various purposes, including transferring sensitive files securely, resuming interrupted transfers, and managing files on remote servers. It empowers users to upload files from their local machine to a remote server or download files from the server to their local machine.
Connection Establishment: To establish a connection with an SFTP server, clients connect to the standard SSH port, usually port 22. This connection initiates an SSH session that shows a secure and encrypted communication channel linking the client and the server.
Client-Server Relationship: SFTP involves both a client and a server component. The SFTP client is software users connect to a server and manage files. Users can store, retrieve, and manipulate files on the SFTP server. When a user interacts with the client and requests a file transfer, the client initiates a secure communication channel with the server.
Data Encryption and Decryption: SFTP uses encryption algorithms to securely move data between the client and the server. These algorithms ensure that the data remains unreadable and confidential during the transfer. This encryption guarantees that sensitive information, such as passwords or file content, remains protected from unauthorized access.
Authentication with SSH Keys: SSH keys are commonly used to automate server access and enhance security. In SFTP, users can use SSH key pairs for authentication. One-half of the key pair (the private key) is stored on the client device, while the other half (the public key) resides on the server. When the keys match, the user is authenticated, allowing secure access without the need for passwords.
Secure Connection Establishment: SFTP utilizes an SSH data stream to establish a secure connection between the client and the server. This connection ensures that all data transferred between the two endpoints is encrypted, maintaining the confidentiality and integrity of the exchanged files.
Choice of Authentication Methods: SFTP provides flexibility in terms of authentication methods. Users can authenticate using various ways, including a user ID and password, SSH keys, or both. This allows organizations to implement security measures that suit their specific needs.
Acknowledgment and Completion: During file transfers, SFTP sends acknowledgments to the client, confirming that the data has been successfully received and stored on the server. Once the transmission completes, the client can disconnect from the secure connection.
Session Termination: When the client has completed its tasks, it can gracefully terminate the SFTP session, disconnecting the secure channel and releasing any assigned resources.

How to Transfer File by Using SFTP?

Here’s a step-by-step guide to the SFTP workflow:

Step 1: Prepare Your Environment:

To connect with the SFTP server, you must first open a terminal or command prompt on your local machine.
It is essential to ensure you have the required credentials, such as username and password or private key, to access the server.

Step 2: Initiate the SFTP Session:

To begin an SFTP session, enter the following command in the terminal:

sftp username@server_address

Replace username with your SFTP username and server_address with the server’s hostname or IP address.
If you’re using key-based authentication, enter the passphrase for your private key when prompted.

Step 3: Navigate Directories:

You’ll see a sftp> prompt when you’re connected. To navigate directories, use common Unix-like commands like:

ls: To view the files and directories in the current remote directory
cd directory_name: If you want to change to a specific directory on the remote server
pwd: To display the current remote directory.

Step 4: Upload Files to the Server:

To transfer a file from your computer to the server, use the “put” command.:

put local_file remote_directory

Replace local_file with the path to the file on your local machine and remote_directory with the destination directory on the remote server.

Step 5: Download Files from the Server:

To download a file from the server to your local machine, use the get command:

get remote_file local_directory

Replace remote_file with the remote server’s file path and local_directory with the target directory on your local system.

Step 6: Other Useful Commands:

mkdir directory_name: To create a directory on the remote server
rm file_name: To delete a file on the remote server
rmdir directory_name: To remove an empty directory on the remote server

Step 7: Close the SFTP Session:

To end the SFTP session, type exit or bye.

List of Common SFTP Commands

SFTP uses a set of commands similar to traditional FTP (File Transfer Protocol). However, these commands are sent securely through the SSH tunnel. Some common SFTP commands include:

Command	Description
put	Upload a file from your local system to the remote server. This command transfers files from your computer to the remote SFTP server.
get	Download a file from the remote server to your local system. This command retrieves files from the SFTP server to your computer.
cd	Change the active directory path on the remote server. This allows you to navigate to different directories on the server.
pwd	Display the current remote working directory. It shows you the directory you are currently in on the remote server.
Icd	Change the local system’s directory path. This command allows you to navigate to different directories on your local system.
lpwd	Display the current local working directory. It shows you the directory you are currently in on your local system.
ls	Display the contents of the remote working directory. It lists the files and directories in the current directory on the remote server.
lls	Display the contents of the local working directory. It lists the files and directories in the current directory on your local system.
lmkdir	Create a local directory. This command creates a new directory on your local system.
lumask	Change the umask value for newly created local files and directories. The umask determines the default permissions for new files and directories.
rename	Rename a file on the remote host. This command allows you to change the name of a file on the remote server.
rm	Delete a file on the remote host. It’s used to remove files from the remote server.

Advantages

Below are the different advantages:

Security: SFTP is well-known for its high levels of security. During transmission, it encrypts data to prevent eavesdropping and unauthorized access. SSH authentication offers secure user verification, making it highly resistant to hacking and data breaches.
Authentication Methods: SFTP supports a variety of authentication techniques, including password-based, public key, and multi-factor authentication (MFA). This adaptability enables organizations to select the level of protection that best meets their needs.
Data Integrity: SFTP protects data integrity through built-in integrity checks during file transfers. This means that transferred files are validated to be unchanged, lowering the chance of data corruption.
Portability and Platform Independence: SFTP is available on various platforms and operating systems, giving it a versatile alternative for organizations with diverse settings. Clients and servers can interact without concern for the underlying systems.
Firewall and NAT Friendly: SFTP runs over a single secure connection, making it compatible with firewalls and Network Address Translation (NAT). Unlike FTP, which requires separate control and data connections that may cause firewall problems, SFTP’s single connection simplifies network configurations.
Automated File Transfers: SFTP is easily integrated into automated processes and scripting, making it useful for scheduled or batch file transfers, backups, and data synchronization.
Compliance Requirements: SFTP is frequently used to meet compliance standards such as PCI DSS, HIPAA, and GDPR, which require safe data transfer and storage practices.

Disadvantages

Below are the different disadvantages:

Complex Setup and Management: Compared to regular FTP, setting up and installing an SFTP server and handling SSH keys can be more difficult. Organizations may require additional skills to ensure proper implementation.
Performance Overhead: Compared to unencrypted file transfers, the encryption and decryption processes during SFTP transfers can cause performance overhead. However, advances in encryption technologies have mitigated this concern.
Compatibility and Adoption: While SFTP is commonly supported, legacy systems or outdated software may not support SFTP. Compatibility concerns could develop in such circumstances.
Limited Directory Listing Support: Unlike FTP, the secure nature of SFTP makes it more difficult to provide extensive directory listings. While SFTP can still give directory listings, client and server implementations may vary.
Learning Curve: It may be necessary for users and administrators to become knowledgeable about the SFTP command-line interface or client software, but this could be Learning Curve for those who are used to working with traditional FTP.

Security Measures

Security is of the utmost significance when using the Secure File Transfer Protocol (SFTP). This section outlines the implementation of critical security measures required to protect data confidentiality, integrity, and availability during file transfers.

1. Hardening the SFTP Server

Hardening the SFTP server means improving its security by reducing potential vulnerabilities. Consider the following steps:

Disable Unused Services: To enhance server security, we recommend disabling any services or protocols that are not in use.
Regular Software Updates: Regularly updating the operating system and SFTP software with the newest security patches is critical to address known vulnerabilities.
User Privileges: When assigning user privileges, it is best to assign users only the minimum necessary privileges for their specific tasks. Avoid using the root account for SFTP activities.
Firewall Configuration: Configure firewalls to restrict incoming and outgoing network traffic to only essential SFTP ports and IP addresses. This will help to reduce the attack surface and make your server more secure.

2. Network Security

Ensure secure data transmission and network access for SFTP by considering these measures:

SSH Encryption: Use vital encryption techniques for the SSH connection to prevent data eavesdropping during transit.
Virtual Private Networks (VPNs): To enhance security, VPNs are recommended to encrypt all traffic between the client and server, providing an additional layer of protection.
Demilitarized Zone (DMZ) Setup: Place the SFTP server in a DMZ to isolate it from the internal network and reduce potential attack vectors.

3. Data Protection

Ensuring the protection of the transferred data remains a primary concern. Implement these safeguards:

Encryption at Rest: Encrypt files on the server at rest to ensure the data stays secure even if the server is compromised.
Transit Encryption: To avoid unauthorized interception, enforce the usage of encryption during data transfer.
Data Integrity: Implement checksums or digital signatures to ensure that files remain unmodified after transfer.

4. Monitoring and Auditing

Maintain visibility into SFTP activities and detect potential security breaches:

Logging: Enable logging of SFTP sessions in detail, including login attempts, file transfers, and administrative tasks.
Auditing: Regularly review logs for anomalies or suspicious activity, and take necessary action upon identification.

5. Regular Security Audits

Periodically perform security audits and assessments of the SFTP environment:

Vulnerability Scans: Run vulnerability scans regularly to uncover any server configuration flaws.
Penetration Testing: Engage in ethical hacking to simulate possible attacks and uncover vulnerabilities that automated scans may not identify.

6. Employee Training

Ensure that your staff is well-trained in security best practices:

User Education: Train users on secure password practices, recognizing phishing efforts, and ensuring the security of their private keys.
Security Awareness Programs: Regularly update employees on emerging security threats and educate them on the importance of following security rules.

Difference Between FTPs vs SFTP

Factor	FTPS (FTP Secure)	SFTP (SSH File Transfer Protocol)
Protocol	FTPS is an extension of FTP	SFTP is a separate protocol
Security	Relies on SSL/TLS encryption	Uses SSH for encryption and authentication
Port	Typically uses port 21 (control) and port 989/990 (data)	Typically uses port 22
Authentication	Supports various authentication methods, including username/password, certificates	Primarily uses public key authentication
Key Management	Involves managing SSL/TLS certificates	Requires managing SSH key pairs
Data Encryption	Data can be encrypted during transfer (optional)	Data is encrypted by default during the transfer
Data Integrity	Limited integrity checks	Provides built-in integrity checks
Firewall/NAT Support	May require additional configuration due to separate control and data connections	Easier to configure through firewalls and NAT
Platform Independence	Available on multiple platforms	Also available on various platforms
File Listing	It may require additional configuration for secure directory listing	Secure directory listing is inherent
Server Software	Supports multiple server software options (e.g., ProFTPD, vsftpd)	Usually uses OpenSSH server or similar
Client Software	Different FTPS clients are available	SFTP clients are widely available
Compliance	Commonly used for PCI DSS compliance	Commonly used for regulatory compliance

Conclusion

SFTP is one of the best protocols that provide data security and transmit data. It can transfer the data by just dragging the files with lightning speed. It is efficient and hence is used very widely. If you wish to send files to a user or another server, SFTP is the solution.

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Introduction to SFTP

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