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Alex

Alex

scp is a program for copying files between computers. It uses the SSH protocol. It is included by default in most Linux and Unix distributions. It is also included in the [Tectia SSH}(/products/tectia-ssh/) and OpenSSH packages

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Alex

Alex

Security in FTP is provided by employing SSL/TLS protocol for channel encryption as defined in RFC 2228. The secured version of FTP is called FTPS.

In UNIX systems another security standard has grown. It was SSH family of protocols. The primary function of SSH was to secure remote shell access to UNIX systems. Later SSH was extended with file transfer protocol – first SCP (in SSH 1.x), then SFTP (in SSH2). Version 1 of the SSH protocol is outdated, insecure and generally not recommended for use. Consequently SCP is not used anymore and SFTP gains popularity day by day.

“SFTP” abbreviation is often mistakenly used to specify some kind of Secure FTP, by which people most often mean FTPS. Another (similar) mistake is that SFTP is thought to be some kind of FTP over SSL. In fact SFTP is an abbreviation of “SSH File Transfer Protocol”. This is not FTP over SSL and not FTP over SSH (which is also technically possible, but very rare).

SFTP is a binary protocol, the latest version of which is standardized in RFC 4253. All commands (requests) are packed to binary messages and sent to the server, which replies with binary reply packets. In later versions SFTP has been extended to provide not just file upload/download operations, but also some file-system operations, such as file lock, symbolic link creation etc.

Both FTPS and SFTP use a combination of asymmetric algorithm (RSA, DSA), symmetric algorithm (DES/3DES, AES, Twofish etc.) and a key-exchange algorithm. For authentication FTPS (or, to be more precise, SSL/TLS protocol under FTP) uses X.509 certificates, while SFTP (SSH protocol) uses SSH keys.

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