Is it possible to write to the same file at different locations using cuda c?

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C

I want to write an encryption algorithm works in ECB mode. I choose CUDA and I started studying the CUDA_C_Programming guide. For my algorithm, the input is the video file. Is it fine, getting the input from the host and do the processing in the device and writing back results to the host? When I write the results, it should be written parallel at different locations in a file? is my idea work out in cuda c? please give suggestions.