I am currently working on a project that deals with sensitivity customer data, and we are being recommended to use Digital Signatures as appose to Electronic Signatures due to its new scale and the sensitive nature of the customers' data.
I personally don't know what the legal issues are with Digital Signatures, but I know that sometimes a Certificate Authority are needed?
This program is being written in C# visual studios if that matters, but I don't really know where to start with this process. I know it works like a public and private key encryption , a Public Key Infrastructure, but I have been informed that you must "buy" a certification from a Certificate authority. You could also create your own?
I was also informed that I need to make sure this would also allow documents created by our program to be legally binding in the USA. That certain laws and procedures are different in different countries so I need to make sure these are in order before I even start coding.
I'm sorry if this sounds more like a legal question then a coding question. My searches aren't helping and I can't start coding until I know what I can and can't do.
SSL encrypts the data channel. It can be broken by the NSA and perhaps others but it is considered quite hard to do so.
I certainly think it is a reasonable and appropriate level of data security for many uses, but that is merely my personal opinion.
Digital Signatures do not encrypt your data. Digital signatures sign your data, assuring you and the recipients that the data was not changed en route, and giving you confidence that you know who signed the data.
You can use a digital certificate purchased from a certificate authority to sign data. Or you can create a self-signed key for your organization and then use subordinate signer keys. We have many many customers who do this.
Documents signed with digital signatures are legally binding everywhere in the world. In some jurisdictions, for some purposes, you need a qualified digital signature. That means that the certificate was issued to the signer by a recognized national certificate authority.
I suggest that you are a ways from coding--you need to better understand your business requirements first.
With digital signatures, protecting the security of the signers' private keys is extremely important. These days, centralized hardware-hardened appliances are often used.
Here are some APIs which make it easy to digitally sign documents and data while managing the keys via an appliance.
Disclosure: I work for CoSign.
Related
I see the term "x509 profile" being used in a technical document on PKI that I am reading, but no explanation is given. I googled for what a "x509 profile" means but the results were not helpful. For example the wikipedia entry on x509 contains phrases like:
IPSec can use the RFC 4945 profile for authenticating peers.
The OpenCable security specification defines its own profile of X.509 for use in the cable industry.
And no where is the definition of a profile given. It seems it is assumed that the meaning of a profile is a given!
What exactly is a profile in x509 context? I know, from the word I can imagine it means some form classifications of x509, but the question is: what makes up this classification? What characteristics of an x509 are used to form these classifications/profiles? Where can one view all available classifications?
A minimal certificate consists of a Name and a Public Key. The CA which signs this certificate asserts that the entity named owns the private key which matches this Public Key.
In addition to this, a certificate can (and more often than not, must) contain additional information. Examples are Issuer and Version fields, and Key Usage, Enhanced Key Usage and Subject Alternate Name extensions.
A certificate profile is a definition of the additional information. For example, section 5.1.3.2 Key Usage of RFC 4945 says:
A summary of the logic flow for peer cert validation follows:
If no KU extension, continue.
If KU present and doesn't mention digitalSignature or nonRepudiation (both, in addition to other KUs, is also fine), reject cert.
Section 5.1.3.6 goes on to describe the Subject Alternate Name expected for IPSec certificates.
Basically, the profile is a definition of how a certificate is expected to be generated for a certain use-case.
You can define your own certificate profiles, but you'd need to have a very good reason to do so. Most use-cases have been covered by existing profiles, so you may end up re-inventing the wheel.
RFC 5280 defines a profiles for X.509 certificates and CRLs for use on the Internet. It lists what is expected of a certificate by services operating on the Internet (as opposed to other networks such as X.25). The fields are fixed (section 4.1) and it also defines standard extensions. In addition to those, you can also define your own extensions. However, you'd need CAs that can create those certificates and clients that understand what to do with them.
I'm planning on using an online contract form where customers will agree to certain terms and conditions and sign with an electronic signature (using the mouse to spell their name). I'm wondering if this type of signature should be encrypted or if this information doesn't really need the extra layer of protection. Ideally I think having the extra layer of protection would be a good choice, but I'm a little strapped on cash.
You can get certificate for free from Let’s Encrypt. Its better than nothing.
First of all, a bit of background - the actual questions are at the bottom.
I'm currently working on a web-based app (sort of SaaS) which allows users to send forms to their own customers.
These forms are simple, small contracts for small jobs where their customers say "Yeah sure, I'll do this and here's my confirmation".
The sort of thing that is being "signed" does not require a fully qualified digital signature and an electronic signature will suffice.
While, in this case, a simple checkbox saying "Yeah, I'll do this" would legally be sufficient, I'm keen to implement it with a signature pad. To be honest, it's just for the factor of being seemingly more binding and, well, "neat".
The current workflow looks like this:
User's customer opens web-form (the party being asked to sign is the only person in the universe to know the direct link)
Ticks a few boxes and enters text
Clicks "Sign" which opens an HTML5 signature pad (mobile) or a simple input (PC) to type their name
Clicks "Accept"
A PDF is generated for download and stored on the server (along with timestamp, IP, and a couple of other bits of information)
As you can see, the agreement in its entirety constitutes a simple electronic signature - even without the bells and whistles.
What I would like to do
As with any simple electronic signature, it's easy for any party to say that a document may have been tampered with.
So what I did is properly sign the PDF according to the specifications (using tcpdf): that entailed first generating the PDF and then adding the signature to the /Sig dictionary, then generating a digest across all byte-ranges (excluding the signature), linking it up with a .crt file and voilá: the document is signed with the lovely benefit of the signature becoming invalid if even a single byte is changed.
Now to the questions:
Is it possible to benefit from the "tamper-validation" without using a certificate? Like I say, these are not supposed to be digital signatures but rather simple, electronic signatures. Still, I'd like to benefit from any post-signature changes being highlighted.
Alternatively, I could also simply use a proper certificate for the signing process. But this certificate would be mine rather than my users' or even my users' customers'. In that sense, would it do more harm than good? I.e. the certificate belongs to the wrong party and therefore becomes meaningless; I, rather than the signatory vouches; "The document was changed and re-signed after I signed"; etc.
Is it possible to benefit from the "tamper-validation" without using a certificate? Like I say, these are not supposed to be digital signatures but rather simple, electronic signatures. Still, I'd like to benefit from any post-signature changes being highlighted.
No, at least as long as you want to do this in an interoperable way.
You can of course invent your own security system, create a PDF viewer or at least plugins for the commonly used PDF viewers to support your system, and roll these programs out to your users.
But if you want existing Adobe Reader as-is to verify the signature, you've got to go the X509 PKI way.
Alternatively, I could also simply use a proper certificate for the signing process. But this certificate would be mine rather than my users' or even my users' customers'. In that sense, would it do more harm than good? I.e. the certificate belongs to the wrong party and therefore becomes meaningless; I, rather than the signatory vouches; "The document was changed and re-signed after I signed"; etc.
When using your own certificate for signing, don't forget to properly fill the reason field so it indicates that your signature is applied as a counter signature to guarantee validatability.
With that in place I don't see your signature doing any harm.
The question is how much good it does, though.
Obviously the user still can claim that he signed something different... because he did! He signed the web form, not the PDF. Thus, you might have to provide proof that the PDF reflects exactly what the web form showed anyways, that the user signed something equivalent.
If you want actual non-repudiation by the user, you need to make him sign personally in a manner that is commonly accepted to not allow tampering. In other words, your user needs to apply proper digital signatures himself. Everything else is open to claims of forgery.
You can use trusted time-stamp (defined in RFC3161) instead of signature created by the customer or by your server. Time-stamp protects document integrity and proves that your document existed before a particular time. Technically speaking it is a digital signature created by a trusted 3rd party.
Immagine a web application that lets you digitally sign (with personal digital certificates pkcs12 released by trusted CAs) and timestamp PDF documents with a Java applet or Active X. This must obviously happen on the machine of the user because the private key of the certificate is stored locally.
So once the PDF is signed and timestamped it is uploaded on the server.
Does the uploaded file have the same features of the one created locally? Does it have sense to talk about "the original version of the file"?
I'm a bit confused on this.
Correction:
i mean digitally sign a document with the private key of a personal digital certificate (should be pkcs7, pkcs12) to ensure that it has really been signed by someone and not someone else.
If by "the original version of the file" you mean that you intend to "freeze" the document so that nobody can ever make changes to it again - that is neither possible nor the purpose of a digital signature. Anyone could simply "cut out" the a signature embedded within a document, nobody would notice.
Protecting a document from subsequent modification involves some kind of DRM mechanism. For example, "watermarking" involving steganography is used to protect photos so that noone should be able to claim ownership of a photo, even after having modified it. But the technology is not very advanced yet, most algorithms can be easily broken.
This implies that the notion of "the original version of the file" in let's say a legal dispute is something that the involved parties have to agree upon in consent. There's no way to prove origin without either consent or a trusted third party that will attest the integrity of a document, e.g. if they have an independent copy of the document.
Apart from that, uploading a file should not change its contents. The file will have the exact same properties than the local one including the signature that was added on the client side.
The signature will only attest authenticity and integrity of the document. If it is vital for your application to be able to tell that the signed document received is actually the one that was expected, then I'd advise you to do the following:
Create the PDF on the server
Create a hash of the document (same algorithm that will be used by the signature applet)
Send the PDF to the client
Let the client sign it and send it back
Compare the client's hash with the one previously computed on the server
Validate the signature
Validating the signature will ensure integrity and authenticity, comparing the hashes will guarantee you that the signed document you received on the server is indeed a signed version of the original document previously created.
Concerning timestamps using local clocks: they're worthless, it's very easy to cheat. What you actually should use there is RFC 3161-compliant cryptographically secured timestamps, issued by a trusted third party. Currently that's the only reliable way to include the notion of time in PDF signatures. There's also built-in support for this in Adobe Reader for example. As these services are generally not available for free, it would make sense to add such a timestamp on the server after receiving the signed document. They are added as an unsigned attribute to the CMS (Adobe still speaks of PKCS7) signature, so it won't break the signature and can safely be added after signature creation.
Okay, let's try to answer your question (as I understand it).
You have some software which uses some private key (and a clock) to add a signature to a file.
This signature is depending on the contents of the file, and thus makes sure that the signer knew (or could have known) the contents of the file at the time it signed it. (There are some ways to have "blind signatures", but I assume this is not the case here.)
Uploading the signed file anywhere does not change anything here.
About the timestamp: The key holder can put in any timestamp it wants - so this only helps if you want to prove knowledge of the document at some point in time against the key holder, not if you are the key holder and want to prove that you signed at some point in time and not earlier or later. (Also, are you sure his clock is not skewed?)
About whether this is legally relevant, you will have to ask your lawyer. It might depend on
the jurisdiction in which the signature happened, and the one in which you want the signed document to be valid
whether the owner of the key had a chance to actually read the document before signing
whether the owner of the key had actually a choice of signing or not.
If you use some applet or ActiveX control in the user's browser, I would not be totally sure that the last two points really hold.
I have three questions regarding SSL that I don't fully understand.
If I get it correctly, a server A submits a request to a certain CA. Then, it receives (after validation etc.) a digital certificate composed of a public key + identity + an encription of this information using the CA's private key.
Later on, a client B wants to open an SSL communication with A, so A sends B its digital certificate.
My question is can't B just take this certificate, thus stealing the identity A - which will allow them to authenticate as A to C, for example. I understand that C will decrypt the certificate with the CA's public key, It will then encrypt its symetric key which will only be decryptable by the real A.
However, I do not see where authentication comes to play if B can actually steal A's identity. Unless I am missing something.
Second question: Why use hashing on the certificate if a part of it is already encrypted by the CA? Doesn't this mean that no one can mess around with a digital certificate (in high probability) anyway?
If I am stackoverflow and I have 3 servers doing the same thing - allowing clients to access, read, identify etc. - do I have to have a different digital certificate for each of the 3 servers.
Thank you very much.
An SSL identity is characterized by four parts:
A private key, which is not shared with anyone.
A public key, which you can share with anyone.
The private and public key form a matched pair: anything you encrypt with one can be decrypted with the other, but you cannot decrypt something encrypted with the public key without the private key or vice versa. This is genuine mathematical magic.
Metadata attached to the public key that state who it is talking about. For a server key, this would identify the DNS name of the service that is being secured (among other things). Other data in here includes things like the intended uses (mainly used to limit the amount of damage that someone with a stolen certificate can do) and an expiry date (to limit how long a stolen certificate can be used for).
A digital signature on the combination of public key and metadata so that they can't be messed around with and so that someone else can know how much to trust the metadata. There are multiple ways to handle who does the signature:
Signing with the private key (from part 1, above); a self-signed certificate. Anyone can do this but it doesn't convey much trust (precisely because anyone can do this).
Getting a group of people who trust each other to vouch for you by signing the certificate; a web-of-trust (so called because the trust relationship is transitive and often symmetric as people sign each others certificates).
Getting a trusted third party to do the signing; a certificate authority (CA). The identity of the CA is guaranteed by another higher-level CA in a trust chain back to some root authority that “everyone” trusts (i.e., there's a list built into your SSL library, which it's possible to update at deployment time).
There's no basic technical difference between the three types of authorities above, but the nature of the trust people put in them is extremely variable. The details of why this is would require a very long answer indeed!
Items 2–4 are what comprises the digital certificate.
When the client, B, starts the SSL protocol with the server, A, the server's digital certificate is communicated to B as part of the protocol. A's private key is not sent, but because B can successfully decrypt a message sent by the other end with the public key in the digital certificate, B can know that A has the private key that matches. B can then look at the metadata in the certificate and see that the other end claims to be A, and can examine the signature to see how much to trust that assertion; if the metadata is signed by an authority that B trusts (directly or indirectly) then B can trust that the other end has A's SSL identity. If that identity is the one that they were expecting (i.e., they wanted to talk to A: in practice, this is done by comparing the DNS name in the certificate with the name that they used when looking up the server address) then they can know that they have a secured communications channel: they're good to go.
B can't impersonate A with that information though: B doesn't get A's private key and so it would all fall apart at the first stage of verification. In order for some third party to impersonate B, they need to have (at least) two of:
The private key. The owner of the identity needs to take care to stop this from happening, but it is ultimately in their hands.
A trusted authority that makes false statements. There's occasional weaknesses here — a self-signed authority is never very trustworthy, a web of trust runs into problems because trust is an awkward thing to handle transitively, and some CAs are thoroughly unscrupulous and others too inclined to not exclude the scum — but mostly this works fairly well because most parties are keen to not cause problems, often for financial reasons.
A way to poison DNS so that the target believes a different server is really the one being impersonated. Without DNSsec this is somewhat easy unfortunately, but this particular problem is being reduced.
As to your other questions…
Why use hashing on the certificate if a part of it is already encrypted by the CA? Doesn't this mean that no one can mess around with a digital certificate (in high probability) anyway?
While keys are fairly long, certificates are longer (for one thing, they include the signers public key anyway, which is typically the same length the key being signed). Hashing is part of the general algorithm for signing documents anyway because nobody wants to be restricted to signing only very short things. Given that the algorithm is required, it makes sense to use it for this purpose.
If I am stackoverflow and I have 3 servers doing the same thing - allowing clients to access, read, identify etc. - do I have to have a different digital certificate for each of the 3 servers.
If you have several servers serving the same DNS name (there's many ways to do this, one of the simplest being round-robin DNS serving) you can put the same identity on each of them. This slightly reduces security, but only very slightly; it's still one service that just happens to be implemented by multiple servers. In theory you could give each one a different identity (though with the same name) but I can't think of any good reason for actually doing it; it's more likely to worry people than the alternative.
Also note that it's possible to have a certificate for more than one service name at once. There are two mechanisms for doing this (adding alternate names to the certificate or using a wildcard in the name in the certificate) but CAs tend to charge quite a lot for signing certificates with them in.
My question is can't "B" just take this certificate, thus stealing the identity of "A" - which will allow them to authenticate as "A" to "C"
There's also a private part of the certificate that does not get transmitted (the private key). Without the private key, B cannot authenticate as A. Similarly, I know your StackOverflow username, but that doens't let me log in as you.
Why use hashing on the certificate if a part of it is already encrypted by the CA?
By doing it this way, anyone can verify that it was the CA who produced the hash, and not someone else. This proves that the certificate was produced by the CA, and thus, the "validation etc." was performed.
If I am stackoverflow and I have 3 servers doing the same thing - allowing clients to access, read, identify etc. - do I have to have a different digital certificate for each of the 3 servers.
It depends on the particular case, but you will likely have identical certificates on each.
First question: You are correct about what you get back from the CA, but you are missing part of what you need before you submit your request to the CA. You need (1) a certificate request, and (2) the corresponding private key. You do not send the private key as part of the request; you keep it secret on your server. Your signed certificate includes a copy of the corresponding public key. Before any client will believe that B "owns" the certificate, B has to prove it by using the secret key to sign a challenge sent by the client. B cannot do that without A's private key.
Second question: Typical public-key cryptography operates on fixed-size data (e.g., 2048 bits) and is somewhat computationally expensive. So in order to digitally sign an arbitrary-size document, the document is hashed down to a fixed-size block which is then encrypted with the private key.
Third question: You can use a single certificate on multiple servers; you just need the corresponding private key on all servers. (And of course the DNS name used to reach the server must match the CN in the certificate, or the client will likely balk. But having one DNS name refer to multiple servers is a common and simple means of load-balancing.)
In general, yes, if the cert file gets stolen, nothing will stop someone from installing it on their server and suddenly assuming the stolen site's identity. However, unless the thief takes over control of the original site's DNS setup, any requests for the site's URL will still go to the original server, and the thief's server will stay idle.
It's the equivalent of building an exact duplicate of the Statue of Liberty in Antarctica with the expectation of stealing away New York's tourist revenue. Unless you start hacking every single tourist guide book and history textbook to replace "New York" with Antarctica, everyone'll still go to New York to see the real statue and the thief will just have a very big, green, complete idle icicle.
However, when you get a cert from a CA, the cert is password protected and cannot simply be installed in a webserver. Some places will remove the password so the webserver can restart itself without intervention. But a secure site will keep the password in place, which means that any server restarts will kill the site until someone gets to the admin console and enters the PW to decrypt the cert.
Question N°1
can't B just take this certificate [...] which will allow them to authenticate as A to C
This part of the a larger diagram deals with that question.
Mainly : if you only have the public key then you can not establish an SSL connection with any client because you need to exchange a secret key with them and that secret key has to be encrypted using your public key, which is why the client asks for it in the first time. The client is supposed to encrypt the shared secret key with your public key and you are supposed to decrypt it using your private key. Since you don't have the private key, you can't decrypt the secret exchange key, hence you can't establish any SSL communication with any client.
Question N°2
Why use hashing on the certificate if a part of it is already
encrypted by the CA?
This is also answered in the original diagram by the question "what's a signature ?". Basically, we're hashing the whole certificate to be sure that it hasn't been tampered with (data integrity), that nobody has changed anything in it, and that what you see is really what was delivered by the CA. The diagram shows how hasing makes that possible.
Question N°3
If I am stackoverflow and I have 3 servers [...] do I have to have a
different digital certificate for each of the 3 servers.
This is not necessarily always the case. Consider the situation where all three servers are on the same domain, then you only need one certificate, if each of them is on its own subdomain you can have one single wildcard certificate installed on all of them.
On the contrary, if you have one server that hosts multiple domains you would have one single multi-domain SSL certificate.
I also have some answers.
Q1) If B steals A's certificate and try to impersonate as A to C.
C will validate the IP address of B and find out that it does not belong to C. It will then abort the SSL connection. Of course, even if C sends an encrypted message, then only the Real A will be able to decrypt it.
Q2) A certificate is usually represented in plain-text using the common format X.509. All entries are readable by anyone. The hashing process is used to digitally sign a document. Digital signing a certificate makes the end user validate that the certificate has not been altered by anyone after it was created. Hashing and encrypting the content using the issuer's private key is done to create a digital signature.