Hello, my name is Shelley Gu and I am a Program Manager on the Trustworthy Computing Security team. I’d like to introduce some new features we have added to digital signatures in Office 2010. First I’ll briefly explain what digital signatures are and how to use them, and then I’ll dive into the details about how they work in Office 2010.
More and more business transactions are being conducted electronically. Consequently, digital signatures are being used increasingly to legally bind relying parties to their transactions. A digital signature is used to verify the identity of the person who signed the document, and confirms that the content was not modified after the digital signature was applied to the document. Digital signatures provide security based in encryption technologies and help mitigate risk associated with electronic business transactions. With improvements to digital signing, Office aims to meet the information security needs of enterprises and public sector entities worldwide.
To create a digital signature, you must have a digital certificate, which proves your identity to relying parties, and should be obtained from a reputable certificate authority (CA). If you do not have a digital certificate, Microsoft has partners that provide digital certificates as well as other advanced signature services that are integrated into Office at the Office Marketplace.
In Word, Excel and PowerPoint 2010, a digital signature can be added by going to the Office Backstage View:
A signature line or signature stamp can be added in Word, Excel, and InfoPath by going to the Insert Tab:
A signature line looks like this:
A signature stamp (more commonly used in Eastern Asia) looks like this:
Office 2007, and later versions, use an open signing standard called XML-DSig that replaces the less advanced binary signatures from Office 2003 and earlier versions. XML-DSig represents a signature in a mostly human-readable XML format. For more information on XML-DSig, see http://www.w3.org/Signature.
Office 2010 digital signatures are able to use advanced algorithms (like the elliptic curve public key algorithm) supported by Windows Vista and later. All supported operating systems also allow the use of more robust hashing algorithms, like SHA-512.
The most immediate problem with digital signatures is that the certificate you use will expire – usually in as little as one year. After the certificate has expired, no one should trust the signature. If you want to be able to trust a signature over a longer period, then you must keep copies of the information needed to validate the certificate. You might also need to worry about the cryptography becoming obsolete.
Fortunately, a solution to these problems is available in an extension to the XML-DSig standard called XAdES.
XAdES (XML Advanced Electronic Signatures) is a set of tiered extensions to XML-DSig, the levels of which build upon the previous to provide more and more reliable digital signatures.
By implementing XAdES, Office complies with the European Union Advanced Electronic Signature Criteria in Directive 1999/93/EC as well as a new Brazilian government directive which defines XAdES as the accepted standard for digital signing in Brazil.
Office 2010 can create different levels of XAdES signatures on top of XML-DSig signatures:
The Office 2010 Beta only creates up to and including XAdES-T signatures, but Office 2010 RTM will be able to create all the signatures in the above table.
Time stamping digital signatures (XAdES-T signatures) is an important scenario we focused on in Office 2010. In order to create a time stamped signature, you’ll need to:
Once everything is configured, you can just create signatures like you normally would. A timestamp from a trusted timestamp server extends the life of your signature, because even after the certificate expires, the timestamp proves that the certificate had not expired at the time of signing. As a result, time stamping protects against certificate expiration, and if the certificate was revoked after the signature was applied, the signature is still valid.
By default, Office 2010 creates XAdES-EPES signatures. Registry settings are used to specify the level of signatures to create. There are two registry settings to control the type of signature Office creates, XAdESLevel and MinXAdESLevel.
The MinXAdESLevel setting allows you to ensure that created signatures meet your required XAdES level. A XAdES-T or higher signature will fail if the timestamp server isn’t available, and a XAdES-C or higher signature will fail if revocation information isn’t available. Having a minimum setting allows scenarios where you could attempt a XAdES-X-L signature, but fall back to XAdES-EPES if the timestamp server is down.
To create XAdES-T signatures and above you will need to provide Office with a time stamp server to query for time stamps:
If you want to create XAdES signatures, we recommend using one of three levels:
Sam wants to create XAdES-X-L signatures. If this is not possible, he is willing to accept any signature that is at least a XAdES-T signature. He sets:
In this case, Office attempts to create a signature up to the –X-L level. If Office is unable to create a XAdES-X-L signature, Office falls back to the last successful XAdES level provided that the level is not lower than MinXAdESLevel. In this case, XAdES-T, XAdES-C, and XAdES-X signatures would be acceptable if Office is unable to create a XAdES-X-L signature. Otherwise, Office does not add a signature.
As mentioned previously, Office 2010 Beta is only able to create up to XAdES-T signatures because we added the rest of the XAdES work in after the Beta. The XAdESLevel registry setting we explained above still applies, but the maximum level is 2 (XAdES-T). TheMinXAdESLevel setting isn’t present, but you can only create two types of XAdES signatures – with and without a timestamp, which is controlled by the TimestampRequired setting (which isn’t present in the RTM version).
To create a XAdES-T signature, you will additionally need to set TimestampRequired (below) and TSALocation (see explanation above):
The XAdES feature is one of many security enhancements we have made to Office 2010. Thanks for reading, and we look forward to hearing your feedback!
I've read in Word 2010 help that "Notarization" is one of the assurances that a signature help establish in Office 2010. Would you please clarify this point? I don't understand it.
Thanks in advance
Q1. What will happen if I try to verify a doc signed in 2010 in office 2007/Office 2007 ?
Shelly, how can i use nationale algorithms, e.g. GOST (national standrd in Russia), for digital signatures in Office 2010?
Word 2010 is crashing when I try to digitally sign a word document. I've tried reinstalling Office 2010, with no success.
Me too..I have the same problem that smukerji faces.
I have the same problem as Office User and smukerji when trying to digitally sign the document it crashes.
Interesting no response or patch from MS!
smukerji, Office User, and Patrick:
Could you give a little more detail about what your workflow was leading up to the crash? What type of signature are you trying to create, etc.? If you would like us to follow up offline, please email the blog with your email address. Thanks.
The error happens as soon as I insert the digital signature in a document. I receive the message “Microsoft Word has stopped working”, which gives me two options: “Check online for a solution” or just “Close the program”.
I've recorded the steps, but I don’t know how to send you the zipped file.
Digital signatures are a nice idea but in reality a huge headache....how can we be sure everyone is using Office 2007 or better? When trying to email from within Office, you get an error saying it will break the signature...none of this is acceptiable. There doesn't seem to be any standardization so no one can reliably send docuemnts to each other and ensure they can view them....what F$cking good is that?
It looks like Office 2010 Beta doesn't support certificates with private keys stored in third-party CSPs on Windows 7 and Vista. Word, Excel, PowerPoint fail to sign documents with such certificates. The CAPI2 event log shows a failure in CryptAcquireCertificatePrivateKey that is being called with CRYPT_ACQUIRE_ONLY_NCRYPT_KEY_FLAG, which means that it doesn't try to use legacy CryptoAPI.
Is this the intended behavior or it is going to be fixed by the release? Thanks.
Great news, just one question: where do you set-up the signature policies?
Great to see XAdES being adopted in Office 2010.
Dissappointed though that looking at the signature produced the content of most of the elements of the XAdES object in the _xmlsignatures\sig1.xml were empty.
Is there a beta available with the completed XAdES object?
Will OneNote 2010 support digital signatures? OneNote would be perfect for a electronic laboratory notebook if only it supported digital signatures for intellectual property purposes.
Thanks for information, with delay. Questions:
1. Will Office 2010 support XAdES-A form (Archival electronic signatures)?
2. I cannot find signature policy in Office 2010 XAdES-EPES form (Explicit policy Electronic Signature). Where is signature policy (ETSI TR 102 038)?
3. I can find in the sig1.xml: "uri.etsi.org/.../v1.3.2. But, latest version is V1.4.1 since 2009-06 (ETSI TS 101 903). Will you change this?
4. When I open Office 2003 signed document in Office 2010, message is: "Invalid Signature". Why?