Each of my limited edition prints come with several unusual features to help complicate attempts at forgery, unauthorized reproductions, and outright fakes, and aid in authenticity verification. They are...
- A cryptographic signature, in both plain text and encoded as a machine readable QR code, on the back of each print which can be independently verified by any cryptography expert and even most crypto-hobbyists.
- Details of each print are recorded in a publicly accessible, downloadable online git repository, which also includes the source for this website. Each update to the repository is also cryptographically signed to provide assurance that I, and only I, made that update.
- A unique acrylic pigment mark next to the serial number on the back of each limited edition print, photographed in high resolution and recorded for posterity in the above mentioned git repository.
An ongoing challenge in the art world is that of authenticity of provenance, or verifying that a work of art was created by the artist it claims to be by, and not a forgery or unauthorized reproduction.
History is full of examples of people discovering that a work of art that they paid a small fortune for is, in fact, a forgery and not worth near the price paid.
There are many ways to attempt to verify the authenticity of a work of art, but new technologies are making it easier and easier for forgers to create fakes, and it's a virtual arms race for those in the business of authenticating art to stay one step ahead.
I hold no delusions of grandeur that my prints will ever be so valued by society that it will ever be worth a forger's time and effort to produce & sell copies. Countless artists far more talented that I can ever hope to be have never been discovered, their lovingly crafted work resold at garage sales to people that had no idea the work was an original or even cared who the artist was.
Never-the-less, I find the subject fascinating and can't help but think that a little effort up front could potentially make the job a lot more difficult for potential forgers and copy-cats.
Furthermore, as a software engineer by profession with a fascination in cryptography, I realized that there were some unique steps I could take to protect my art and make it a little more difficult for someone to forge copies of my prints.
There is no procedure or tool to make a piece of art 100% forge proof. Given sufficient time, resources, and motivation, a skilled forger can make copies of a piece of art that could convince all but the most experienced and skilled authenticity experts.
However, should anybody ever decide to try to make reproductions of any of my limited edition prints, or create entirely new prints of photos I never took, and slap my name on them to inflate the value, I hope to make the task a bit harder for them.
For each of my limited edition prints, I create a description of the print, including the title, year, size, serial number, materials used, etc. I then sign that description with my private key and include the full description and signature on the back of the print, in both a plain text human readable form, and in a machine readable (i.e. your smart phone) QR code. Since each print description contains information that is 100% unique to that specific print (i.e. the serial number), the signature on each print is also 100% unique to that print.
My public key is published for the world on major public keys servers (fingerprint: ED97 F43E 1D86 6D62 31BB 04AD D2DE C6AA 316B 5CDD). Any cryptography expert, and most cryptography hobbyists, should be capable of taking my public key, and the QR code on the back of any of my prints, and verifying that the signature matches.
It is beyond the scope of this article to explain the concept of cryptographic signatures in depth, but I'll provide links at the end to further reading and tools for those that are interested.
For a grossly oversimplified analogy though, imagine a good old fashioned wax seal. In the Middle Ages, aristocrats used wax seals to, among other things, authenticate documents that they were signing. Everybody knew what Count Geoffrey's seal looked like, so when you saw a document with his seal, you could be reasonably sure that Geoffery had signed it.
Cryptographic signatures work similarly, except through the power of math and prime numbers. Wait! Stay with me, I'll try to keep this short.
In this case, the stamp (the thing you press into the wax) is a pair of really, really, really, big prime numbers. This pair of numbers is called the "private key." Count Geoffery randomly selects a pair of huge prime numbers, and then he keeps these prime numbers (his private key) very, very secret.
To sign (or stamp) a piece of text, Geoffery runs the text, and his private key (the prime numbers), through a specially crafted mathematical algorithm, and it spits out a long stream of what appears to be random letters, numbers and other symbols, which is called the "signature". It's not at all random though, and as crazy as this sounds, only that text, and those prime numbers can produce that particular signature.
In our analogy, that stream of characters (the signature) represents the wax, stamped with Count Geoffery's stamp, on the back of a letter, and allowed to harden. Anybody that receives that text, with that signature, can verify, with mathematically certainty, that Count Geoffery signed it.
"But how?" you ask. Well, in addition to Count Geoffery's private key (the two prime numbers), he also has what's called a "public key", which is simply the two prime numbers multiplied together. Imagine if Geoffery's private key was the prime numbers 17 and 47 (these aren't nearly long enough in reality, but bear with me). Geoffery's public key then would be 17 x 47, or 799.
There's no known way to figure out what two prime numbers were multiplied together to get 799, other than just trying all of the possibilities, which is why, other than for simplified explanations like this, Count Geoffery would want really, really, really big prime numbers. So, Count Geoffery can safely broadcast his public key (799) to the whole world and know that his private key (17 and 47) is safe and secure.
Finally, to verify that a letter of admiration, claiming to be from Count Geoffery, is really from him, Princess Carisa merely needs to run the text, the signature, and Geoffery's public key (799) through another specially crafted mathematical algorithm, and the algorithm is able to verify (through the magic of math) that the prime numbers used to generate the public key were also used to generate the not-so-random signature. If the verification passes, Carisa knows that Geoffery's letter is genuine. But if it fails, then the Pricness knows that somebody else is trying to impersonate Geoffery.
Further reading for the mathematically masochistic;
Unique details (including a high resolution photo of the pigment mark on the back) of each limited edition print are recorded in a publicly accessible online git repository to aid in authenticity verification.
Each commit to the repository is signed with my public key (see the section on cryptographic signatures).
I currently maintain the repository on github, but on the off chance that any of my prints outlast both myself and github, anybody familiar with git (primarily software engineers like myself) can clone the repository to their local machine right now and even upload it to another git hosting service for long term safe keeping.
Since each commit is signed with my public key, anybody sufficiently familiar with git and cryptography will be able to verify that the details on each print were submitted by me, and not by someone that cloned and then modified the commit history.
Within the description on the back of each limited edition print, in close proximity to the serial number, I add a unique mark of acrylic paint.
After allowing it time to dry, I take a high resolution macro photograph of the mark and include the photo with the details of the print in the online git repository as a permanent record associating that serial number with that unique mark of paint.
It is my intent to make these marks nearly impossible to copy and reproduce. The photos are of high enough resolution that microscopic details in how the pigment attached to the paper, and even the cotton fibers in the paper itself, are readily visible.
Feel free to click on the sample on the right, and then zoom in.
As long as they properly verify the source of the photo of the mark, any qualified art authenticity expert should be able to use a strong magnifying glass or microscope and compare the image to the actual mark and confirm with relative ease that they are identical, or that the print is a forgery.
I believe that creating a sufficiently perfect replica of the pigment mark purely by hand would be impossible for even the most skilled counterfeiter. One might optimistically argue that eventually 3D printers may achieve the resolution necessary to accomplish the task. I highly doubt that, but authenticators can also check the positions of the cotton fibers in the paper itself.