theHarvester is an open source OSINT tool that gathers the following information about a public resource:
- Subdomain names
- Employee names
- Email addresses
- PGP key entries
- Open ports and service banners
For some of its data, like employee names and PGP keys, theHarvester uses general search engines like Google and Bing to gather information. It also searches certificate information directly from Comodo's certificate search engine. For additional information, theHarvester searches social media sites like Twitter and LinkedIn. Its banner grabbing functionality relies on Shodan.
The tool is relatively simple to use, yet can help you automate many information gathering tasks.