Introduction
Transferring files over a network is essential for any organization, whether sharing documents internally or enabling secure access for customers and partners. However, the traditional File Transfer Protocol (FTP) has significant security vulnerabilities…
FTP vs. FTPS vs. SFTP
FTP sends data including usernames, passwords, and file contents unencrypted as plain text. This allows potential attackers to steal credentials and sensitive documents by sniffing network packets…
FTPS adds Transport Layer Security (TLS) encryption to encrypt the FTP session and prevent packet sniffing. However, FTPS still transmits unencrypted metadata revealing actions like login attempts and file names…
SFTP, or SSH File Transfer Protocol, runs file transfers over an encrypted SSH session for better overall security. All session data, file contents, and file names are encrypted end-to-end…
Use Cases for SFTP Servers
Common uses for SFTP servers include…
Step 1: Install and Configure OpenSSH Server
SFTP relies on the SSH protocol for securely transferring files. The OpenSSH server package provides the sshd daemon and utilities to handle SSH sessions and encryption…
Generating SSH Keys for Added Security
Using SSH key-based authentication instead of password login provides an additional layer of security for SFTP and shell access…
Configuring the SSH Daemon
Edit the OpenSSH daemon configuration file /etc/ssh/sshd_config to enable the SFTP subsystem. This allows segregating SFTP users from shell access for more control…
# SFTP settings
Match Group sftp
ChrootDirectory
ForceCommand internal-sftp
# Other options
ChrootDirectory confines users to their home directories…ForceCommand restricts users only to SFTP…Other options like X11Forwarding, TCP forwarding, and PORT forwarding can be disabled for higher security…
Step 2: Create SFTP Users and Groups
User accounts can be selectively given SFTP access without allowing SSH shell access. For easier management, create a dedicated SFTP group…
# Add system group for SFTP
sudo groupadd sftp
sudo useradd bob -m -g sftp
sudo passwd bob
For teams, separate SFTP groups can be created with differing permissions to provide tiered access to select folders…
Step 3: Set Directory Permissions
Tightly restrict filesystem permissions to prevent unauthorized access or modifications…
Step 4: Connect via SFTP for Secure Transfer
SFTP Performance Benchmark
The encryption used in SFTP introduces additional CPU overhead, which can reduce top transfer speeds compared to plain FTP…
Harden SFTP Security
Techniques for additional hardening include:
- Automated user access reviews
- Failed login attempt thresholds
- Monitoring for suspicious activity
- Restricting SFTP client types
- Limiting cipher suites
Troubleshooting SFTP Issues
Common problems and solutions:
- Authentication failures: Check configured keys, passwords…
- Connection timeouts: Verify firewall rules, routing…
Conclusion
With this comprehensive SFTP server guide, you can securely transfer files while avoiding the pitfalls of regular FTP. Employing encrypted transfers, restricted accounts, isolated folders, and other security measures helps protect sensitive data.