Asking for suggestions
This is definitely not a good format for our site, as you point out.
Would it be approbate to rewrite the body of the question to more specifically ask for the motivation of RSA-OAEP, what it does, and why?
Rather than doing this yourself, I recommend using the comments to:
- Point out that "any suggestions?" is not a good format for our site
- Suggest to the question asker that they make these kinds of changes to:
- Improve the reception of their question
- Get more/better answers
- Avoid their question being closed.
If we do it this way, then they will learn how to ask better questions in the future.
Mentioning that the changes will improve reception and get more/better answers is positive motivation; I find that users are more receptive to the feedback when the positive motivation is included in the comment.
Very old questions
Of course, such a question may be very old and the user that asked it no longer active. In this case, the above recommendation is unlikely to work.
Making substantive changes runs the risk of changing the askers intent. This is especially concerning if they will not be around to comment on whether or not any changes were appropriate.
If what they are asking could not be interpreted in another way, then making these types of changes would appear to be harmless. But, if the question was clear, I'm not sure this meta topic would be applicable to it.
Case 1: Old Unanswered questions
Rather than making substantive changes to another users question, I would say to ask a well-formed question and close the old unanswered question as a duplicate of the new well-formed one.
Case 2: Old questions that were answered
If we are to stick to not making substantial edits, then there appears to be little choice here but to make the suggestions in the comments and move on. In this case it's probably a good idea to highlight how this format is not a good fit for our site.
Fortunately, I expect this situation to be relatively rare.