How to start working with sftp?

i’m trying to create my first SFTP (ftp + ssh2) client but i don’t know where to start or what kind of libraries i can use. my previous code was in c language using libssh2 library build by mingw (windows) which suppose to work on linux too so i kinda have some knowledge about sftp. the problem, when i wanted to re-create the project to work with freeRTOS i couldn’t find where to start.
as far as get is i need to use ssh2 and ftp separately (which is not the case when i used the libssh2 but it’s ok i don’t have problem with that) but what are the ssh library and the ftp library i can use, is there any library for them or i need to create my crypt function and start from scratch building the ssh protocol and then move on the the ftp protocol (this will take too much) and i don’t think those standard protocols doesn’t have library works for freeRTOS.
maybe i’m missing something and the answer would be too simple so i hope you can bear with me a little bit and sorry for the stupid question.

There are several open source crypto libraries around. Take a look at WolfSSL, mbedTLS and libCrypto. The HTTPS demo in the FreeRTOS Labs section uses mbedTLS. If commercial software is ok for you then there are many more options.

thanks for you fast replay and your suggestions but is there any ssh library. because i do want to try to build an SFTP client which is FTP over SSH, if i use SSL/TLS then that will be FTPS(FTP over SSL/TLS). i probably will try that but it will be after SFTP client and maybe server too. and for the https section, it’s not what i’m looking for. it’s a navigator and server communication (web applicatio), FTP is a transfer file application. i will have a look for the others sections like the FAT section if i’m not mistaken.
thank you for your help.