What is the answer to the riddle about "what force and strength cannot get through"?

The answer to the riddle is a key. The riddle in its entirety asks, "What force and strength cannot get through, I with a gentle touch can do. And many in the street would stand were I not a friend at hand. What am I?" .

Riddles often rely on metaphorical or non-literal language in order to give hints as to what the correct answer is. In this case, the hint to the answer lies in the phrase "at hand," which is intended to allude to the fact that a key fits in one's hand. Without one, many people would stand "in the street," such as when locked out of their own buildings.