stm32 mcu firmware ssh and sftp support

We are producer of industrial GSM modems. We have TCP/IP Stack and we can communicate at TCP level. The structure is simply MCU (STM32F4) + GSM Module. At the MCU side, we have to execute SSH and SFTP functions. SSH is generally used at PC, but our platform is an MCU. So the open libraries spend much memory. We need a library especially for low FLASH and SRAM usage. Requirements : - C language Source code must be delivered with remarks and example project. - Commercial SSH and crypto libraries will not be used, license-free source can be used. - SSH Server and Client must be supported, SSH version 2. - SFTP Server and Client must be supported. - Resultant code must include functions that act as bridge from raw data to SSH and from SSH to raw data. - Maximum SRAM Buffer size will be 30 KB (selectable size with #define), smaller is better! - Functions must be able to handle non-ASCII data buffers (any hex data). - Data transfer must be divided into packages of maximum 1400 Bytes (selectable size with #define) - We have TCP/IP Stack on GSM Module, so the resultant code must use UARTS only, representing the TCP layer. For testing, we will provide a PC program that converts UART data to TCP and vice versa. - 6 months support - The resultant code will be tested on STM32F412RET6 and must be able to communicate with a Linux Machine, on which we will execute these commands (from MCU to Linux and from Linux to MCU) : - SSH - SFTP - SCP