How to implement a "self-authenticating" document - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: September 11, 2018, 09:44:12 am
content: I'm looking for ways to produce a hard copy contract which in its own right is "self-authenticating". Basically, to prove that a particular copy of the contract (and all its individual pages) is authentic. For example, to negate the argument of altered pages replacing original ones.I know the term "self-authenticating" is defined in law in certain countries and one way of creating such a document is to have it signed by a notary, however I'm looking to avoid this option.It needs to be a method which is cheap (or free) but effective. I don't want to start spending money on reams of expensive "security paper" with various watermarks etc... which really doesn't prove anything anyway (another party could argue that I just re-printed an altered contract on the same security paper).The only way I would really think of doing this is to have each party (and witnesses) sign multiple copies of the contract so that each party gets an "original" copy as opposed to a scanned/photocopied version.Does anyone have any other ideas?

author: taydin
author_rank: Frequent Contributor
timestamp: September 11, 2018, 10:36:11 am
content: Taking pictures of that document and then digitally sign the image files will give you what you need. But of course, the jurisdiction that you live in must recognize digital signatures as binding. AFAIK, most countries do nowadays.

author: Kjelt
author_rank: Super Contributor
timestamp: September 11, 2018, 11:21:11 am
content: Quote from: taydin on September 11, 2018, 10:36:11 amWhich key will you use to sign the document and how can some third party without knowledge of said key authenticate the document?There is more needed for "self-authentication" .First thought is that you need a TTP (trusted third party), this should be some notary with a digital verification service or trusted database that stores hashes over the document.

author: taydin
author_rank: Frequent Contributor
timestamp: September 11, 2018, 11:31:46 am
content: Quote from: Kjelt on September 11, 2018, 11:21:11 am"Digitally signing" is the general name for the procedure, and I don't know every step that a jurisdiction requires for it to be binding. But it will:- Ensure that the signed documents have not been altered in any way.- Ensure that those documents were indeed signed by the people in question.

author: jolshefsky
author_rank: Regular Contributor
timestamp: September 11, 2018, 11:40:31 am
content: Quote from: Kjelt on September 11, 2018, 11:21:11 amIn my business, I have customers sign a contract agreeing to purchase and to the company's terms and conditions—which exist in a separate document. But for the purpose of argument, the way I "guarantee" it is that they send a scanned copy of the signed contract back.For your purposes, I think if they sign each page (or initial each page and sign the last which is common in the U.S.) and scan the document and return it, that is enough assurance for you. Should things go in the direction of legal proof, it would be up to them to produce their originally signed document that matched the one they scanned and sent to you. Using even a simple watermarked paper would help for fraud detection, should it ever come to that.One of the challenges is making a system that is sufficiently transparent that everybody knows what is going on. That is, complex technical solutions are difficult to explain how they are effective. Like if somebody sent me a document that was supposedly digitally signed, and I open it and it says it's digitally signed, what the heck does that mean?—it seems easy to have a fraudulent confirmation of authenticity that would look the same to me.

author: Bud
author_rank: Super Contributor
timestamp: September 11, 2018, 12:34:40 pm
content: Quote from: Kjelt on September 11, 2018, 11:21:11 amAny public Certificate Authority would do, such as Entrust, Digicert etc. The problem may be getting a personal digital certificate from one as an individual. If you have a company this is easier. They will run a few checks on you and the company and issue a certificate which you can import in wordprocessing software that supports digital certificates , i believe Adobe Acrobat does. But to verify the authenticity it has to be a electronic version of the document.

author: Bud
author_rank: Super Contributor
timestamp: September 11, 2018, 02:52:02 pm
content: Quote from: jolshefsky on September 11, 2018, 11:40:31 amYes and no. Digital signature primarily is an assurance of the identity of the owner, a document signed by the owner has non- repudiation property, assuring that nobody but the owner of the signing certificate could produce such digital signature. But you are right that the certificate owner can sign altered copies of the document. So other controls should be in place such as the fingerprint/hash of the digitally signed document which may be printed on each page of the document. Document signing softwares may have that or similar features to assure the integrity of the content. Again that has a limitation you need to keep an electronic copy of the document.

author: ajb
author_rank: Super Contributor
timestamp: September 11, 2018, 05:41:52 pm
content: You still need some sort of trusted way of validating the signature. Even if you sign with a private key, the public key has to be deposited in a trusted location, otherwise at any time you could create a new key pair, sign a new document, and just say "no, *this* is the public key we signed against, honest!" Even if both parties to a document sign it, and store each others public keys along with the document, then at any time either party could alter the document and create two new signatures from new key pairs. Then you have to figure out who is presenting the original keys and who is presenting the fakes!So one way or another, you need an out-of-band way of verifying that the claimed public keys are the same ones that were used in the original signing. You could use an open public key server if you trust it sufficiently, or you could have a printed copy of your public keys notarized, or I guess you could use a certificate from any of the major signing authorities.

author: onesixright
author_rank: Frequent Contributor
timestamp: September 11, 2018, 06:24:16 pm
content: Hash it. Put the hash in a blockchain.Sent from my iPhone using Tapatalk

author: Kjelt
author_rank: Super Contributor
timestamp: September 11, 2018, 09:02:40 pm
content: Quote from: onesixright on September 11, 2018, 06:24:16 pmAnd which secure hash will last for lets say 40 years ?What if the hash algo is hacked who will and can re-authenticate all the docs?

author: amyk
author_rank: Super Contributor
timestamp: September 12, 2018, 02:04:31 am
content: Use several of them together (yes, even the currently broken ones like MD5) if you're really that paranoid. You might be able to make an altered document that collides one of the hashes, but good luck colliding all of them...

author: tggzzz
author_rank: Super Contributor
timestamp: September 12, 2018, 07:29:00 am
content: If you have aselfauthenticating document, the focus moves to how to authenticate the authenticator.Alternatively, it is trivial to have a self authenticating document - just have theincludedauthenticator always return "valid document".

author: tggzzz
author_rank: Super Contributor
timestamp: September 12, 2018, 07:48:25 am
content: When I was writing contracts, the procedure was:send two signed paper copies to the other partyget them to return one signed paper copycarefully check that no alterations had been made to the contract, e.g. by signing and dating the changesThat became more difficult with PDF documents.When patenting something my employer sent me a document to sign so that I could get a "bonus". It included something like "... make all efforts to ...". No way was I going to agree to that, so I edited the PostScript to "... make all reasonable efforts to ...", printed, signed and submitted that. They didn't noticeLater, after leaving that company, they sent me more (paper) documents with similar clauses w.r.t. progressing the patent in other territories. I carefully inserted the word "reasonable" in several locations, signed and dated those changes. I heard nothing more

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 12, 2018, 09:44:13 am
content: YubikeyEnvoyé de mon iPad en utilisant Tapatalk

author: EEVblog
author_rank: Unknown
timestamp: September 12, 2018, 10:13:05 am
content: Quote from: Halcyon on September 11, 2018, 09:44:12 amPeople and organisations like wikileaks are now using blockchain to prove a documents authenticity and chronology.

author: onesixright
author_rank: Frequent Contributor
timestamp: September 12, 2018, 10:24:59 am
content: Quote from: Kjelt on September 11, 2018, 09:02:40 pmYou have a point, but this argument is for everything in the digital realm.

author: onesixright
author_rank: Frequent Contributor
timestamp: September 12, 2018, 10:25:42 am
content: Quote from: EEVblog on September 12, 2018, 10:13:05 amThanks Dave 😀

author: Halcyon
author_rank: Unknown
timestamp: September 12, 2018, 10:32:04 am
content: Quote from: tggzzz on September 12, 2018, 07:48:25 amI think I'll just do that. Keep it simple. Of course I will make digital copies (of both) so that the hard copies can always be compared to the digital ones. I don't anticipate there ever being a dispute, but it's an arse covering exercise. If it's good enough for the banks, it's good enough for my purposes.All parties will be signing each of the copies (along with the witnesses) at the same time and location anyway, so it makes collecting and scanning them easy.

author: tggzzz
author_rank: Super Contributor
timestamp: September 12, 2018, 01:10:57 pm
content: Quote from: Halcyon on September 12, 2018, 10:32:04 amWitnesses probably aren'tnecessaryfor a paper document. The legal system places a lot of credence and value in signed papers.A contract can be assumed to have been acceptedimplicitlyand be in force when work starts, even if nothing has been signed. So don't jump the gun!Naturally IANAL, my knowledge is of UK law, but I suspect Antipodean law is similar.

author: Bud
author_rank: Super Contributor
timestamp: September 12, 2018, 02:07:45 pm
content: Quote from: ajb on September 11, 2018, 05:41:52 pmThis is what the public Certificate Authorities are for. They are major companies everyone trust. You do not sign a dociment with just a random key pair. You get one from a CA in form of a Digital Certificate signed by the CA. The CA is THE trusted party. Any good security software will verify the digital signature UP to the trusted Root (the CA).However if there is a very long term validity check requirement this may not be a way to go, because digital certificates have expiry, and once they expire the CA will only store a copy for 3 to 10 years depending on the CA archival policy.Blockchain suggestion looks interesting, as i think the lifetime of a reputable block chain will exceed that of a CA archive.

author: tggzzz
author_rank: Super Contributor
timestamp: September 12, 2018, 02:53:10 pm
content: Some of the replies in this thread, and I'm not pointing the finger at any one in particular, remind me of the old aphorism amongst security practitioners: "If you think encryption will solve your problem, then you don't understand encryption and you don't understand your problem".Start by defining/specifying the threat in a way that can be tested, and develop a mitigation to that threat.Then game-play not how the mitigation can work, but how it can either fail or simply be avoided.Repeat until you have run out of timeExample: "prevent state security reading my documents", mitigation "encrypt the disk". Then the game-plays can be either "you're not leaving without decrypting it" or, more likely in some places, rubber-hose decription techniques. At which point you realise encrypting the disk didn't solve the problem!

author: Bud
author_rank: Super Contributor
timestamp: September 12, 2018, 03:16:40 pm
content: But the topic in discussion is about data Integrity, not Confidentiality. They are separate cryptography domains, OP is not looking to encrypt the data, but to ensure the data was not altered.

author: tggzzz
author_rank: Super Contributor
timestamp: September 12, 2018, 05:00:06 pm
content: Quote from: Bud on September 12, 2018, 03:16:40 pmIndeed, but hashing and blockchains are sufficiently "close" to encryption that the aphorism is relevant here - mutatis mutandis of course.

author: Cerebus
author_rank: Super Contributor
timestamp: September 12, 2018, 05:30:00 pm
content: In the case of digital signatures, the simple answer to the problem of establishing the authenticity of the signing certificate(s) is to physically publish the signing certificate (which can be self-signed) in a newspaper of record, such asThe Times, as a classified advertisement, or in an official journal of record such as theLondon Gazetteas a notice. Back in the day, Ross Anderson published abook of root certificatesas a way of making a durable public record of them.If one was to go down a digital route, all parties to the signed document need to digitally sign it so that there is no single party attesting to the document's authenticity.The classic paper method, which has stood the test of time, is to get the signatories together in one place and have all of them sign multiple copies of the paper contract and each party keeps a copy of the contract, possibly with additional copies held in escrow by banks or lawyers. If there are trust issues or the contract is of particularly high value, then it's customary to initial all pages and possibly have one or more independent third parties sign to witness the signatures of the signatories.

author: technix
author_rank: Super Contributor
timestamp: September 12, 2018, 06:06:27 pm
content: I wonder if the PGP version of all this signing would work. You need to figure out a way to associate your PGP public key to yourself legally, and then use regular PGP document signing to prove its authenticity.As of using a certificate issued from an CA, here in Shanghai any local residents and local businesses can buy a certificate ultimately signed by Government of the Municipality of Shanghai. Signing a document in any form digitally with that certificate - scanned or not, or even just a signed electronic message, will have the same legal effect as signing a physical copy, and the local government will prove the connection between the certificate and the entity upon request.

author: TerraHertz
author_rank: Super Contributor
timestamp: September 13, 2018, 02:49:54 am
content: Quote from: Halcyon on September 11, 2018, 09:44:12 am90% of the replies in this thread wandered off down the digital documents security path. But Halcyon said HARD COPY.He wants a way to verify a PAPER document has not been tampered with.Halcyon, some printed documents that are required to remain controlled, use a system in which they are printed using minute spacing differences between the letters and words, to encode a digital signature. Each copy printed is unique, but looks the same to the human eye.With this, any unauthorized reproduction copies that turn up can be traced to the specific original copy that leaked. Also each page can be verified as original by its own hidden encoding.This of course relies on the antagonist not having your software tools for embedding the spacing encoding.Though if that hidden data is itself encrypted, then good luck to them cracking it even with the software tools.Then there's the way that some (all?) colour photocopiers encode their own serial numbers into documents they print, for law enforcement traceability. They add a pattern of tiny yellow ink dots to each page.Edit: It's not clear from your question WHO you want to be able to verify the document in future. You, or the other party, or both?

author: Halcyon
author_rank: Unknown
timestamp: September 13, 2018, 03:51:17 am
content: Quote from: TerraHertz on September 13, 2018, 02:49:54 amThey do indeed (Steganography) and I did consider this as a method.Anyone should be able to verify the document as being original, but mainly the parties who the document applies.

author: onesixright
author_rank: Frequent Contributor
timestamp: September 13, 2018, 10:55:04 am
content: Quote from: tggzzz on September 12, 2018, 05:00:06 pmClose? I dont think they are the same at all. Not by a long shot, well not IMHO. Please elaborate?