Digital signature

What is a digital signature, does it involve a hash.

(Assuming SSL)
Anthony LuciaAsked:
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Dave HoweConnect With a Mentor Software and Hardware EngineerCommented:
Most cryptographic signatures are in fact the hash of the message encrypted with the signer's private asymmetric key. By decrypting the key using the matching public key, the verifier can obtain the original hash, and hence, match that to a locally calculated value of the message's hash.

However, in the legal form, there is no requirement for this to be the case - a LEGAL digital signature is anything that represents the act of signing a message - hence, a cryptographic signature attached by hand is a legal digital signature; however, simply typing your name at the bottom of an email is *also* a legal digital signature.
Conversely, having a machine attach your name (or a Cryptographic signature) to a message is NOT a legal digital signature - the key is the physical act of will/choice signing the document, not the technology :)
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Patrick BogersDatacenter platform engineer LindowsCommented:
Hi

It means your mail / files are signed by an SSL certificate.
It involves encryption.
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Joe Winograd, Fellow&MVEDeveloperCommented:
Hi Dave,
The Wikipedia article about it is helpful:
http://en.wikipedia.org/wiki/Digital_signature

And here's a short article with a brief definition:
http://searchsecurity.techtarget.com/definition/digital-signature

This is different from a bitmap graphic that is used to put an image of your "real" signature on a document, as discussed in this article:
http://www.experts-exchange.com/Software/Photos_Graphics/Images_and_Photos/A_12380-Signature-Image-with-Transparent-Background.html

Regards, Joe
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BiniekCommented:
You can look into some Microsoft documents online, in my opinion it is presented in an accessible way:

Understanding Digital Certificates
http://technet.microsoft.com/en-us/library/bb123848(v=exchg.65).aspx

Understanding S/MIME
http://technet.microsoft.com/en-us/library/aa995740(v=exchg.65).aspx

Understanding Public Key Cryptography
http://technet.microsoft.com/en-us/library/aa998077(v=exchg.65).aspx

I'd like to recommend to You very good tool - Cryptool - Educational Tool for Cryptography and Cryptanalysis, this is very simple tool, and help You to understand digital signature.
www.cryptool.org - but now the webpage is closed, because they are moving to new serwer
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Joe Winograd, Fellow&MVEDeveloperCommented:
Dave,
One other thing. If your interest is primarily in digital signatures for PDF documents, take a look at this comprehensive white paper (152 pages!) by Bruno Lowagie, the CEO of iText Software:
http://itextpdf.com/book/digitalsignatures20130304.pdf

Regards, Joe
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Dave HoweSoftware and Hardware EngineerCommented:
@Joe: That's an excellent document :)
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Joe Winograd, Fellow&MVEDeveloperCommented:
@DaveH,
I think so, too. Reading it cover-to-cover is on my bucket list. :)
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Dave HoweSoftware and Hardware EngineerCommented:
Well, its quite short compared to this little lot:

http://www.adobe.com/devnet/pdf/pdf_reference.html

I am glad to note that, despite pdf now being a (pay to play) ISO standard, adobe still have it on their website for free download :)
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Joe Winograd, Fellow&MVEDeveloperCommented:
Yeah, I downloaded the 1.6 ref a while ago — 1,236 pages! That one is post-bucket list. :)

Btw, NJD posted a new question that you might want to play in:
http://www.experts-exchange.com/Security/Operating_Systems_Security/Q_28404166.html

Cheers, Joe
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Dave HoweSoftware and Hardware EngineerCommented:
1.7 is even bigger, plus the 1.8/1.9 "extensions" that are still numbered 1.7 now ISO owns the standard :)

As for the other question - I saw it, but it seemed to me you and Giovanni had it covered, so I didn't think my input would help any :)
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Joe Winograd, Fellow&MVEDeveloperCommented:
Thanks for the heads-up on 1.7/1.8/1.9 — haven't even looked at 'em yet!
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