Re-implementing one's own proprietary code as open-source I wrote some software as part of an internship. It worked well for the task and we published a paper on it. However, because the internship was at a company, not my graduate institution, the code is technically property of the company and they do not want to release it. I've received several requests for the code, and I know that releasing the software will increase my paper's citations and impact. Is it okay to re-implement the code I wrote and release it as open source, or could that violate some laws or policies?

For the record, when I say re-implement, I mean start from scratch, not reuse most of the same code and change a few things.
I am not a lawyer, and if you are seriously considering going ahead with this project, I suggest consulting one.

The problem is that copyright infringement is not limited to direct copying. See, for example, the "My Sweet Lord" case. George Harrison is not believed to have consciously copied "He's So Fine", but he had heard it.

You have much deeper familiarity with the existing code. It is going to be very difficult for you to write anything similar without being inspired by what you wrote before.

If your former employer's reluctance to release is related to liability and support issues, they may be willing to permit re-implementation, so it is worth asking. If they are hoping to make money off the code, they will not agree.