SFTP Security – Is It Truly Secure?

Is SFTP enough to keep my files secure when shared? We understand the worry and have compiled ways to keep your data as secure as possible through SFTP.

Is SFTP transfer encrypted? Yes, SFTP encrypts everything being transferred over the SSH data stream; from the authentication of the users to the actual files being transferred, if any part of the data is intercepted, it will be unreadable because of the encryption.

What Is Secure File Transfer Protocol (SFTP)?

SFTP (SSH File Transfer Protocol or Secure File Transfer Protocol) is a secure file transfer protocol used for transferring files over a secure shell. It provides strong authentication and encrypted data transfers between two computers over an insecure network, and is typically used for uploading and downloading files from a remote server.

Businesses use SFTP for its tight security, which is especially important when transferring sensitive or proprietary data. SFTP provides an encrypted connection for data transfers, eliminating the risk of data being accessed by unauthorized users during the process. It also allows for authentication of both the server and the client, ensuring that only the party intended is able to access the data. By using SFTP, businesses are able to securely transfer files between multiple locations and systems, as well as back up data to off-site storage. This also eliminates the need for sending physical hard drives or CDs to transport data. SFTP is also used for website hosting, as it is the most secure form of transfer for web content.

Businesses benefit from using SFTP by having the assurance that data is securely transferred. It allows for fast and reliable data sharing, which can help boost productivity, as well as save time and money. SFTP is also cost-effective, as it does not require additional hardware or software to be purchased. The encryption offered by SFTP also provides an extra layer of security over other data transfer methods, ensuring that confidential information is kept safe.

How Does SFTP Work?

Secure File Transfer Protocol (SFTP) is a secure protocol used to transfer files between two computers over a secure connection. It is a networking protocol that provides encryption, authentication, and data integrity for file transfers. It operates on port 22 and uses SSH to create a secure connection and encrypt data. Once the connection is established, the user can then send and receive files using the SFTP protocol. Files can also be transferred by creating copies of the files within the remote directory or through the use of a script. Ultimately, SFTP provides a safe and secure way to transfer files over the internet.

Security Protocols Used by SFTP

At its core, SFTP relies entirely on the Secure Shell (SSH) protocol to create a secure channel for file transfers, typically over port 22. This fundamentally answers the question, “is SFTP secure?” by confirming its foundation in strong cryptography.

SSH employs a trio of security mechanisms to protect the entire session. First, it uses public-key cryptography for robust authentication, verifying the identities of both the server and the client to prevent impersonation. Once authenticated, it negotiates a strong symmetric encryption cipher, like AES 256 encryption, to ensure all data—including commands, filenames, and file content—is unreadable to eavesdroppers.

Finally, it uses hashing algorithms to check for “sftp data integrity,” guaranteeing that data has not been modified in transit. This multi-layered approach is a significant upgrade from traditional FTP, which transmits all information, including credentials, in vulnerable clear text.

SFTP Setup: Securing Your File Transfers

• Enable and Harden SSH: Your first step is to ensure the SSH service is enabled on your server. Go beyond enabling it by hardening the configuration: disable direct root login, turn off password-based authentication, and explicitly disallow older, vulnerable SSH protocol versions.
• Implement Key-Based Authentication: Create SSH key pairs for users and disable password authentication entirely. This method, where a user’s public key is stored on the server and they authenticate using their private key, is significantly more secure than passwords and is a cornerstone of “sftp security.”
• Configure Strong Ciphers: Do not rely on default settings. In your SSH server configuration file, specify a list of modern, strong ciphers (e.g., “aes256-gcm@openssh.com”), key exchange algorithms (KEX), and message authentication codes (MACs). This prevents downgrade attacks where a client might negotiate a weaker encryption method.
• Limit User Permissions: Apply the principle of least privilege. Use `chroot` jails to confine users to their specific home directories, preventing them from browsing the server’s file system. Set strict file and directory permissions to ensure users can only read or write to authorized locations.
• Test and Monitor Connections: After applying your configurations, thoroughly test the connection to confirm that security restrictions are effective. Implement comprehensive logging and integrate it with a monitoring system to track all SFTP activity, providing a crucial audit trail for compliance and security investigations.

SFTP for Secure File Transfer: Advantages and Disadvantages

SFTP has gained popularity among businesses seeking a secure file transfer solution due to its advanced security features. Like any technology, however, SFTP has its pros and cons. In this section, we will explore the advantages and disadvantages of SFTP to help you make an informed decision on whether SFTP is the right choice for your organization’s file transfer needs.

SFTP Security and Other Advantages

• Security: SFTP uses encryption to secure data in transit, making it a more secure option than FTP.
• Authentication: SFTP uses public key authentication, making it difficult for unauthorized users to access data.
• Portability: SFTP can be used on any platform that supports SSH (Secure Shell), including Windows, Linux, and macOS.
• Integrity: SFTP includes data integrity checks to ensure that the data has not been tampered with during transit.

SFTP Complexity and Other Disadvantages

• Complexity: SFTP is more complex than FTP, requiring a higher level of technical expertise to set up and use.
• Performance: SFTP can be slower than FTP due to the encryption and decryption process involved.
• Limited support: SFTP is not supported by all FTP clients and servers, which can make it difficult to use in some environments.
• Security Issues: While SFTP is more secure than FTP, it is not immune to hacking or cyberattacks. There have been instances where SFTP systems have been breached.

What Is the Difference Between FTP and SFTP?

File transfers are a way of life for most large businesses. However, when it comes to transferring extremely large files, or a large volume of files, or even when batch files need to be transferred quickly, then these companies need to rely on something more than email or flash drives. That’s where File Transfer Protocol (FTP) comes into play.

FTP is one of the oldest protocols around. Built to facilitate direct file transfers between computers, FTP leverages the client-server model of networking to allow users to upload and download files to and from servers quickly.

FTP is lightweight and easy to use, so much so that nearly every operating system has some sort of FTP capabilities in place. Additionally, most operating systems also support several FTP applications to make transfers even easier.

FTPs availability and speed come at a cost, however. FTP transmissions are not encrypted in any way. This means two things:

1. All data, both stored in an FTP server and transmitted between computers, is potentially vulnerable to attack. If someone, for example, intercepts an FTP transmission between computers then the data is open to read as-is.
2. Login credentials are also most likely unencrypted, meaning that this information can also be stolen by a hacker from an FTP server. Furthermore, most FTP servers don’t use advanced authentication measures to protect access to data.

With that being said, FTP is not secure in and of itself, and as such doesn’t meet even the minimum requirements for any compliance framework. Without the necessary security in place, it isn’t a safe solution for protecting data. That’s why most organizations have turned to SFTP.

SSH (or Secure) FTP attempts to address the problem of security by utilizing an encryption algorithm as part of its operation. SFTP includes Secure Shell (SSH) protocol in the storage and transfer process. What does that mean for users? It means that the data is encrypted in the server and during transmission. Should that data be stolen during an SFTP transfer, the thief will not be able to read it without cracking the encryption.

To ensure security, modern SSH protocol uses modern encryption:

1. SSH uses Advanced Encryption Standard (AES) to encrypt data. AES is a symmetric block cipher that leverages complex mathematics and the unique properties of prime numbers to encrypt data with a key, the length of which determines the difficulty of breaking the cipher. Typically, this means the use of AES-128 or AES-256 algorithms, which use a 128-bit or 256-bit key respectively.
2. SSH uses a hashing algorithm, usually SHA-2, to determine data integrity. A “hash” is a unique alphanumeric value created by processing the data through a hashing algorithm. The idea is that if the data is run through the same hashing algorithm, it will produce an identical hash. Accordingly, if data produces a different hash than the one provided, it signals that the data has been modified.

SFTP, using SSH technology, brings these security measures to FTP transfers. Additionally, it allows for additional authentication measures for user access beyond the transfer of clear-text user IDs and passwords.

SFTP vs. FTPS: Which Is More Secure?

While both SFTP and FTPS (FTP over SSL/TLS) offer encryption, their security architectures differ significantly. SFTP is a distinct protocol built on top of SSH, using a single, encrypted channel over one port (typically 22) for all communication. This makes it inherently firewall-friendly and simpler to secure.

In contrast, FTPS is the classic FTP protocol with a layer of TLS encryption, which often requires multiple port openings for control and data channels, increasing firewall complexity and potential misconfiguration risks. FTPS relies on an X.509 certificate infrastructure for authentication, whereas SFTP uses SSH keys.

For most modern applications, SFTP is considered the more robust and secure choice due to its streamlined, single-channel design that encrypts everything from the start. Choose SFTP for superior firewall traversal and integrated security. Choose FTPS only when legacy systems or partner requirements specifically mandate certificate-based authentication over a traditional FTP framework.

SFTP vs. Managed File Transfer (MFT)

SFTP and Managed File Transfer are two popular protocols used for secure file transfer. While both serve the same purpose, there are some key differences between the two file transfer methods.

SFTP is a protocol used for secure file transfer over the internet. It uses encryption to protect data in transit and includes advanced security features such as public key authentication and data integrity checks. SFTP is widely used in organizations of all sizes and is supported by most FTP clients and servers. However, SFTP can be slower than other protocols due to the encryption and decryption process involved.

MFT, by contrast, is a more comprehensive solution for transferring files. It includes features such as automation, scheduling, and workflow management, making it suitable for large organizations that require a more robust solution for file transfer. MFT also includes advanced security features, such as encryption and authentication, to ensure the security of data in transit. MFT, however, can be more complex and expensive to set up and use than SFTP.

When comparing SFTP and MFT, it is important to consider the specific needs of your organization. If your organization requires a simple and secure protocol for file transfer, SFTP may be the best choice. However, if your organization requires a more comprehensive solution that includes automation and workflow management, MFT may be a better fit. Ultimately, the decision between SFTP and MFT will depend on the specific needs and requirements of your organization.

How Encryption Algorithms Work in SFTP

The “sftp security” model is built on a sequence of cryptographic operations that occur during the initial connection handshake. First, the client and server use a key exchange algorithm, such as Diffie-Hellman, to securely generate a shared secret session key without ever transmitting it over the network. This prevents eavesdroppers from intercepting the key.

Second, this newly created key is used to initialize a fast and secure symmetric block cipher, like AES (Advanced Encryption Standard). From this point on, every command, filename, and piece of file data is broken into blocks and encrypted, ensuring confidentiality.

Third, to protect “sftp data integrity,” a hashing algorithm like SHA-2 creates a Message Authentication Code (MAC) for each data packet. The receiver independently computes the hash and verifies it matches the sender’s, guaranteeing the data wasn’t altered in transit. This three-pronged approach makes for a truly “secure sftp” session.

How Secure Is SFTP?

SFTP (Secure File Transfer Protocol), as a reminder, is a secure version of the File Transfer Protocol (FTP), which is used for transferring files over the internet. It is a secure protocol, as it provides strong encryption for data transferred over the network, as well as user authentication. It uses Secure Shell (SSH) to encrypt the data and session information, so that the data is not exposed while transferring. Additionally, it allows the server to authenticate the client and the client to authenticate the server before any data is exchanged. This ensures that only authorized users have access to sensitive data. Finally, users can also employ digital signatures to verify the integrity of their data.

SFTP is more secure than FTP, as it encrypts all data transferred between the client and server, including usernames and passwords. Additionally, SFTP requires user authentication, meaning that only authorized users have access to the data. Moreover, SFTP allows the server to authenticate the client and the client to authenticate the server before any data is exchanged, providing an extra layer of security. All of these features make SFTP more secure than FTP.

IT departments prefer using SFTP, as it offers a high level of security for data transferred over the network. It also allows users to easily configure access control, so that only authorized users have access to sensitive data. Furthermore, with SFTP, they can also use digital signatures to verify the integrity of their data. All of these features make SFTP the preferred choice for IT departments.

SFTP Encryption: How Data Is Protected in Transit

The question “is SFTP encrypted” is best answered by examining how it protects data in transit. The entire SFTP session, from the initial connection to the final disconnection, occurs within a secure tunnel created by the SSH protocol.

The process starts with a handshake where the client and server perform cipher negotiation. Here, they agree on the strongest set of encryption and hashing algorithms they both support. Once established, all data—user credentials, commands, and file content—is wrapped by the chosen cipher before it leaves the source machine. This ensures end-to-end “sftp encryption” during transit.

Following “sftp security best practices” means configuring your server to only allow modern, robust ciphers like AES-256-GCM or ChaCha20-Poly1305, while explicitly disabling deprecated ones such as RC4, 3DES, and any CBC-mode ciphers, which are vulnerable to attack.

Encryption at Rest on SFTP Servers

While “sftp encryption” is excellent for protecting data in motion, its protections cease once a file is successfully transferred. This makes “sftp encryption at rest” a non-negotiable component of a secure file management lifecycle. Without it, sensitive data stored on the server’s disk is vulnerable to physical theft or unauthorized access by privileged users. To mitigate this, organizations can implement filesystem-level encryption (e.g., BitLocker on Windows Server, LUKS on Linux) to encrypt the entire storage volume.

For more granular control, application-level encryption can be used to encrypt individual files as they are stored. For maximum security and to meet stringent compliance requirements like PCI DSS or HIPAA, using a Hardware Security Module (HSM) to protect the encryption keys ensures they are never exposed. Implementing encryption at rest is a critical control for demonstrating comprehensive data protection to auditors.

Understanding SFTP Encryption Algorithms

• AES-256 (Advanced Encryption Standard): Considered the gold standard for `sftp encryption`. Pros: Virtually unbreakable, trusted by governments for top-secret data. Cons: Can be marginally slower than AES-128 on devices without hardware acceleration. Security Rating: Excellent.
• ChaCha20-Poly1305: A modern, high-performance authenticated cipher. Pros: Extremely fast, especially on CPUs that lack dedicated AES hardware, making it ideal for mobile and IoT devices. Cons: Less ubiquitous than AES. Security Rating: Excellent.
• AES-128: A faster but slightly less complex version of AES. Pros: Offers a great balance of strong security and high performance. Cons: While secure for now, AES-256 is preferred for long-term data protection. Security Rating: Very Good.
• SHA-256/512 (Secure Hash Algorithm 2): Used for message authentication to ensure data integrity. Pros: Highly resistant to collision attacks, providing robust verification that data hasn’t been tampered with. Cons: Not for encryption, only integrity. Security Rating: Excellent.
• Guidance: For a high-risk profile, mandate AES-256. For environments with mixed or older hardware, ChaCha20-Poly1305 is a superior choice. Always pair your cipher with a SHA-2 family hash for integrity.

Choosing the Right SFTP Encryption Algorithm

Choosing the right “sftp encryption” algorithm requires a thoughtful decision framework based on three key factors: regulatory compliance, performance, and interoperability.

First, check any regulatory mandates (e.g., FIPS, HIPAA) that apply to your data, as they often specify approved algorithms like AES.

Next, consider your performance requirements; while AES-256 offers maximum security, ChaCha20-Poly1305 may be faster on systems without AES hardware acceleration.

Finally, ensure interoperability by confirming your clients support the chosen algorithms. For a quick comparison: use AES-256 for maximum security and compliance, ChaCha20-Poly1305 for best performance on non-specialized hardware, and AES-128 for broad compatibility with a strong security baseline. Always prioritize authenticated encryption (AEAD) ciphers to ensure both confidentiality and integrity.

Is PGP Encryption Needed with SFTP?

Layering PGP encryption over SFTP is a powerful strategy for specific high-security scenarios. While “secure sftp” protects data in transit, PGP provides persistent, end-to-end file-level encryption. This is advisable in zero-trust architectures where the SFTP server itself cannot be fully trusted, or when files must traverse multiple hops before reaching their final destination.

A PGP-encrypted file remains indecipherable even if the SFTP server is compromised or during long-term storage, ensuring only the intended recipient with the correct private key can ever access its contents. This approach is vital for compliance with regulations that require provable data segregation and protection at rest. However, for simple point-to-point transfers to a trusted, secure server with robust “sftp encryption at rest,” adding PGP can introduce unnecessary key management complexity without a proportional increase in practical security.

How Does SFTP Authentication Work?

Secure File Transfer Protocol (SFTP) authenticates users by using public-key cryptography. This requires the user to upload a public key to the server, which is used to verify the user’s identity. When the user attempts to log in, the server uses the public key to generate an encryption key that the user must use to log in. The server then decrypts the key the user entered, verifies the user’s identity, and then allows the user access to the server.

Multi-Factor Authentication and SFTP Security

Multi-Factor Authentication (MFA) dramatically elevates “sftp security” by adding another layer of verification beyond a password or a private key. Even if an attacker steals a user’s private SSH key, they are still blocked without the second factor.

Common MFA methods compatible with SFTP include Time-based One-Time Passwords (TOTP) from authenticator apps, push notifications to a mobile device, or hardware tokens like YubiKeys. SSH can be configured to require both a valid key and a one-time code, a method known as “publickey,keyboard-interactive.”

Implementing MFA is one of the most effective “sftp security best practices” for preventing unauthorized access. During compliance audits for standards like CMMC or PCI DSS, having MFA in place serves as powerful evidence that you are taking proactive and robust measures to secure access to sensitive data.

What Issues Might Businesses Face With File Transfer and GDPR Compliance?

SFTP, when configured correctly, can help with GDPR compliance. However, it isn’t necessarily so out of the box for a few reasons:

• SFTP doesn’t stop the unauthorized transfer of data to third parties. This can lead to non-compliant disclosures of data, which breach GDPR rules on confidentiality and privacy.
• SFTP doesn’t manage cross-script vulnerability. FTP transfers are often automated, as is SFTP. However, because automation scripts and applications can sometimes expose data outside of the SFTP application, they provide an attack surface for hackers. Data exposed in outside scripts will breach GDPR.
• SFTP does not include centralized audits or documentation. Most compliance frameworks, including GDPR, require some documentation to demonstrate compliance. SFTP can include audit logs, but without a centralized SFTP server documenting access across multiple systems can make documentation hard and raise red flags for assessors. Likewise, documentation must also adhere to privacy laws, which becomes exponentially more difficult over multiple SFTP servers.
• SFTP doesn’t natively support file and folder expiration needed for regulations and internal policies. Many frameworks require automated access automation so that files aren’t open into perpetuity.
• SFTP doesn’t natively provide encryption at rest. This is a configuration that an admin must make, which usually entails that it is being modified for other purposes.

While SFTP can support compliance more broadly, the technology is not necessarily compliant out of the box.

What Can I Do to Make Sure My SFTP Server Is Secure?

There are several approaches you can take to better secure your SFTP servers to support compliance:

1. Disable FTP. If you are using your own server, disabling FTP is a good way to lock down a potential attack vector. Likewise, if you work with a third-party vendor, you can ask if they have disabled FTP and, if not, what security protocols they have in place to protect it.
2. Use the strongest encryption. AES-256 is currently the strongest standard encryption around, and SHA-2 hashing currently represents the strongest hash encryption to authenticate data. It’s straightforward to get an SFTP server that includes both.
3. Use file and folder security for external access. Have proper practices in place to monitor and protect data when third parties need to see it during or before an SFTP transfer. This includes proper user access and identity management features.
4. Use folder security for internal access. Access controls can be a pain to set up because somebody has to do it manually on individual folders. Business users typically don’t have the skills or permission to do this, so organizations often resort to these users writing help desk tickets for IT to undertake access management tasks. The Kiteworks platform has a solution that provides web-based (or even mobile) self-service for business users to set and automate these security settings.
5. Include documentation and auditing. Most frameworks require some capacity to document things like compliance and file access. Utilizing a method to monitor file access as well as document things like user consent and other requests is a critical part of GDPR compliance.
6. Use IP blacklisting and whitelisting. It may be necessary to simply block access to your servers through blacklists to protect data, particularly if there is no reason to accept traffic from, say, foreign countries or specific regions.
7. Provide logging integration with your SIEM so your SOC team can detect and mitigate attacks.
8. Require certificate-based authentication for external users. This way, you can ensure that anyone accessing your system at least has a security certificate to verify who they are.
9. Harden your SFTP server. Once you configure your SFTP server with increased security measures to prevent unauthorized access, data theft, and malware attacks, you’ve hardened it. Access controls, encryption, authentication, and monitoring are additional hardening techniques.
10. Protect the SFTP server behind your corporate firewall, and only expose a proxy tier through your firewall as a DMZ against unauthorized access.

SFTP Automation for Compliance and Efficiency

Automating SFTP workflows is crucial for enhancing security and ensuring compliance.

By automating user lifecycle management, you can instantly provision and deprovision accounts based on HR system triggers, eliminating the risk of lingering access. Scripted transfers ensure that sensitive data moves reliably on schedule without manual intervention, which dramatically reduces the chance of human error.

Furthermore, automated monitoring and alerting for anomalies—such as transfers to unusual locations or large volume deviations—enable your security team to respond to potential threats in real time.

For compliance frameworks like GDPR or SOX, this automation provides an unimpeachable, consistent audit trail, making it simple to collect evidence and prove that data handling policies are being enforced systematically.

Achieve SFTP Security With Kiteworks

The Kiteworks Private Data Network consolidates your third-party communication channels, such as SFTP, email, file sharing, managed file transfer, web forms, and application programming interfaces (APIs), onto a single platform, empowering organizations to control, protect, and monitor every piece of sensitive content that comes into or goes out of your organization. This allows for the secure sharing and transfer of sensitive files in compliance with data privacy regulations and standards.

With Kiteworks SFTP, organizations securely transfer confidential files to and from remote servers, with strong encryption measures in place to protect sensitive information like customer records, account information, and personally identifiable information and protected health information (PII/PHI). Kiteworks SFTP utilizes secure SSH key exchange technology to facilitate encrypted file transfers that are safe and secure. Users as a result can send large files and folders quickly and securely from any device, including mobile devices. To be clear, Kiteworks’ SFTP solution is designed for ease of use, allowing users to integrate secure file transfer with existing workflows so content security doesn’t compete with business productivity.

Kiteworks SFTP offers a range of security features, such as multi-factor authentication, access controls, secure deployment options, a hardened virtual appliance, and encryption at rest. These and other security features ensure that sensitive content is protected at every stage of the transfer process while also supporting compliance with major regulations like the Health Insurance Portability and Accountability Act (HIPAA), the Cybersecurity Maturity Model Certification (CMMC), Federal Risk and Authorization Management Program (FedRAMP), Payment Card Industry Data Security Standard (PCI DSS), SOC 2, FIPS 140-2, the General Data Protection Regulation (GDPR), and others.

To learn more about Kiteworks’ SFTP and compliance features, schedule a custom demo of Kiteworks today.

Additional Resources

• Blog Post Top Enterprise SFTP Software for Clients & Servers
• Video What You Need to Know About Kiteworks SFTP Capability
• Blog Post What Is SFTP Hosting? How to Find the Best Provider
• Blog Post What to Look for in Top SFTP Servers for Secure File Transfers
• Blog Post Top 5 Secure File Transfer Standards to Achieve Regulatory Compliance