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This feature is used to add security informations in a message which will be used to handle authorizations and access rights.

== Implementation ==

=== Specifications ===
The reference for the implementation of this functionality is the [http://www.ietf.org/rfc/rfc2634.txt RFC&nbsp;2634]


=== Architecture ===

==== Synthetic presentation of the architecture of the extension ====

This functionality is in the list of features to be implemented by the Mozilla foundation: http://www.mozilla.org/projects/security/pki/nss/smime/. So, it is integrated to the source code of Thunderbird, without relaying on an extension. Furthermore, this make more simple the addition of this functionality, because we need to update the heart of the product.

The heart of this implementation is to add attributes to the signature of a message. A message with a Security label must be signed. When receiving such a message, theses attributes are decoded in order to handle authorizations and access rights.

==== GUI files ====

To send a message with Security label, it is mandatory to sign the message. So, the Security Label is bound to the security layer.

At the GUI level, signing is implemented by a flag ''signMessage'', encapsulated in a [http://www.xulplanet.com/references/xpcomref/ifaces/nsIMsgSMIMECompFields.html nsIMsgSMIMECompFields] object. The whole code handling this flag is contained in the JS built-in library ''msgCompSMIMEOverlay.js''.

Then, the object [http://www.xulplanet.com/references/xpcomref/ifaces/nsIMsgSMIMECompFields.html nsIMsgSMIMECompFields] is forwarded to the XPCOM layer, that handles the signing. So, this class has been updated to add a flag for the Security label. Furthermore, the GUI has been updated so that the user can choose this Security label.

==== XPCOM files ====

===== Message sending =====

The implementation is mainly located in the file ''nsMsgComposeSecure.cpp'' in the [http://www.xulplanet.com/references/xpcomref/ifaces/nsIMsgComposeSecure.html nsMsgComposeSecure] class.

This implementation mainly consists in adding attributes in the signature of a message.
When sending a message, the built-in Thunderbird API build the following data structure :

[[Image:SignedReceipt_struct1_fr.gif]]

The attributes to add are located in the structure ''NSSCMSSignerInfo'' and are of type ''NSSCMSAttribute''.

A ''NSSCMSAttribute'' structure is defined as:

[[Image:SignedReceipt_struct2_fr.gif]]

The attribute to add is a ''securityLabel'', which structure is defined by the [http://www.ietf.org/rfc/rfc2634.txt RFC&nbsp;2634].

===== Message receiving =====

When receiving a message with a Security label, this structure is decoded.