Another obstacle is the requirement to physically meet with someone (for example, at a key signing party) to verify their identity and ownership of a public key and email address, which may involve travel expenses and scheduling constraints affecting both sides. A software user may need to verify hundreds of software components produced by thousands of developers located around the world. As the general population of software users cannot meet in person with all software developers to establish direct trust, they must instead rely on the comparatively slower propagation of indirect trust.