Does it take long to implement RSA in hardware?
RSA will not be easy to implement and may require a very large FPGA.  RSA is far better suited to running on a general purpose CPU than an FPGA.  I have seen some implementations of RSA on an FPGA that use a softcore to run the algorithm and the FPGA to accelerate some of the math, but the complete algorithm is not implemented in Verilog.  And generally when a file is "RSA encrypted," it usually isn't - the file is generally AES encrypted and the AES key is then RSA encrypted since AES is much faster than RSA.  If you want to implement an encryption algorithm on an FPGA, especially for a streaming signal, AES would be a much better idea than RSA.  You can probably implement AES in a week, it's a pretty simple algorithm.