FreeFileSync needs libssh2, while WinSCP does not.

When it comes to connecting to an SFTP server, FreeFileSync needs libssh2, while WinSCP does not. Here is the breakdown of how each application handles SFTP connections under the hood:

1. FreeFileSync: Yes, it needs it

FreeFileSync relies directly on libssh2 as its core backend engine to handle SSH and SFTP network protocols.

• How it works: FreeFileSync packages libssh2 directly into its application code (or links against the system’s libssh2 library on Linux). When you enter an sftp:// address into FreeFileSync, it uses libssh2 to perform the SSH handshake, authenticate your keys or password, and run the file synchronization.
• Do you need to install it? No. FreeFileSync includes it automatically, so you don’t need to download or install libssh2 separately.

2. WinSCP: No, it does not need it

WinSCP does not use libssh2 at all. Instead, it uses code derived from PuTTY (specifically psftp) as its underlying SSH/SFTP engine.

• How it works: Because PuTTY is one of the most mature, secure, and widely adopted open-source SSH implementations for Windows, the author of WinSCP chose to integrate PuTTY’s internal code directly into WinSCP to manage SFTP connections.
• The .ppk Connection: This is why WinSCP natively uses PuTTY’s private key format (.ppk) rather than standard OpenSSH keys.

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