Why a fern.
A digest is the right proof and the wrong picture. We wanted both.
Every e-signature service can tell you that a document hasn't changed since it was signed. They do it with a SHA-256 digest: 64 characters that nobody reads. When two digests differ in one character, almost no one notices.
A fern is an iterated function system: four small transformations repeated thousands of times. Feed its parameters from the digest and the result is a plant that belongs to exactly one file. People are good at telling plants apart. A changed contract looks changed.
The fern doesn't replace the digest. The certificate prints both, and our Verify tool compares the digests. The fern is how you notice there is something to check.
FernSign Inc. is based in New York. We build electronic signing for small firms that sign real agreements every week: leases, change orders, offer letters, NDAs.