kychee-com/kysigned

kysigned is a way to get legally meaningful e-signatures on a document using nothing more than email, instead of a dedicated signing app or account. A signer receives an email with the document attached, forwards it back with the words I sign this document as the first line, and that is the entire signing process from their side. No account, no password, no separate app to install. The clever part is what makes that forwarded email trustworthy as proof. Every email provider already attaches a cryptographic seal called DKIM to outgoing messages, mainly to prevent spoofing. kysigned uses that existing seal as the actual signature: since only the real provider can produce that seal for that sender's address, nobody else could have forged the forward. The tool checks that the forwarded attachment is byte for byte identical to the original document, stamps the time it arrived twice for extra durability, and keeps a public timestamped record of the DKIM key used, so that even if an email provider later changes or exposes its keys, an old signature cannot be faked or denied afterward. Once everyone involved has signed, every party gets one PDF evidence bundle that anyone can check on their own computer, even with no internet connection and even if the kysigned service itself no longer exists. There are two ways to use it. The simplest is to sign documents directly at kysigned.com, paying a small fee per document with no setup required. The other is to deploy your own copy of the entire application, using a hosting platform called run402 that handles the email, database, and server pieces for you, so your instance runs under your own domain rather than the original one. A deployed instance can also be controlled through an MCP server, letting an AI assistant like Claude send a document for signature and check its status on your behalf. This is aimed at developers or small businesses who want low cost, verifiable signatures they can fully control and self-host, rather than a general consumer product. It requires comfort with the command line and environment variables to run your own instance, though using the hosted version needs none of that.