Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The key in a dream is sustenance, help, victory, and knowledge. Whoever sees many keys in his hand will gain a great kingdom and authority, as Allah says, 'To Him belong the keys of the heavens and the earth.' A wooden key is a hypocritical man. Whoever opens a door with a key will achieve his need and triumph over his enemy.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
The key in a dream is the opening and facilitation of matters. It may also indicate an answered prayer, a male child, or a spy. Whoever finds a key has found a treasure or useful knowledge. Losing a key indicates difficulty in matters and loss of knowledge or money.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The key is interpreted as a knowledgeable man, a ruler, or one who holds the solution to matters. Opening a locked door with a key indicates relief after hardship and achieving one's desire. A key made of iron is a strong, powerful man, and one of gold is a rich man.