The SSH Page (Advanced Site Settings dialog)

The SSH page on the Advanced Site Settings dialog allows you to configure options of SSH protocol and encryption.

To reveal this page you need to select SCP or SFTP file protocol on Login dialog.

More SSH options are available on subpages:

Key exchange (key exchange and reexchange options)
Authentication (advanced authentication options)
Bugs (detections of known bugs in SSH servers)

Refer to documentation of page sections:

Protocol Options
Encryption Options
Further Reading

Protocol Options

The Enable compression checkbox enables data compression in the SSH connection: data sent by the server is compressed before sending, and decompressed at the client end.

Encryption Options

WinSCP supports a variety of different encryption algorithms, and allows you to choose which one you prefer to use. You can do this by dragging the algorithms up and down in the list box (or moving them using the Up and Down buttons) to specify a preference order. When you make an SSH connection, WinSCP will search down the list from the top until it finds an algorithm supported by the server, and then use that.

WinSCP currently supports the following algorithms:

AES (Rijndael) – 256, 192, or 128-bit SDCTR or CBC, or 256 or 128-bit GCM (This feature is available only in the latest beta release.)
ChaCha20-Poly1305, a combined cipher and MAC
Blowfish – 256-bit SDCTR or 128-bit CBC
Triple-DES – 168-bit SDCTR or CBC
Arcfour (RC4) – 256 or 128-bit stream cipher
Single-DES – 56-bit CBC (see below)

If the algorithm WinSCP finds is below the warn below here line, you will see a warning box when you make the connection:

The first cipher supported by the server is single-DES, which is below the configured warning threshold.

Do you want to continue with this connection?

This warns you that the first available encryption is not a very secure one. Typically you would put the warn below here line between the encryptions you consider secure and the ones you consider substandard. By default, WinSCP supplies a preference order intended to reflect a reasonable preference in terms of security and speed.

In SSH, the encryption algorithm is negotiated independently for each direction of the connection, although WinSCP does not support separate configuration of the preference orders. As a result you may get two warnings similar to the one above, possibly with different encryptions.

Single-DES is not recommended in the SSH protocol standards, but one or two server implementations do support it. WinSCP can use single-DES to interoperate with these servers if you enable the Enable legacy use of single-DES option; by default this is disabled and WinSCP will stick to recommended ciphers.1

You can see actually used encryption algorithm on Server and Protocol Information Dialog.