RealMe is a software suite that uses an image-based public key infrastructure (PKI) that embeds cryptographic information in a digital image and then exchanges pieces of that image between a user and a Web application to accomplish a strong, bi-directional multi-factor authentication. This technology combines steganography with applied cryptography, and results in a secure yet low-cost solution for Web sites that exchange confidential information with their users.
SignPDF is a simple command line application to sign a PDF document. It can sign a PDF document with a valid certificate, encrypt/protect a PDF document, and timestamp a PDF document (optional feature). A JKS keystore with a cert signed by your desired CA is mandatory for use. The tsa_url of a timestamp server can be used to timestamp your documents. The signed PDF file is signed and protected with allowed restrictions to printing, content copying, and content copying for accessibility. By default, SignPDF creates a configuration file at ~/.signpdf, which can be edited for further use.