Data Elements Signed Attribute
| Tag | (0400,0020) |
|---|---|
| Type | Required (1) |
| Keyword | DataElementsSigned |
| Value Multiplicity | 1-n |
| Value Representation | Attribute Tag (AT) |
A list of Data Element Tags in the order they appear at the top level of the referenced SOP Instance that identify the Data Elements used in creating the MAC. See Section C.12.1.1.3.1.1.
Section C.12.1.1.3.1.1
C.12.1.1.3.1.1 Data Elements Signed
The Data Elements Signed Attribute shall list the Tags of the Data Elements that are included in the MAC calculation. The Tags listed shall reference Data Elements at the same level as the Mac Parameters Sequence (4FFE,0001) Data Element in which the Data Elements Signed Attribute appears. Tags included in Data Elements Signed shall be listed in the order in which they appear within the Data Set.
The following Data Elements shall not be included either implicitly or explicitly in the list of Tags in Data Elements Signed, nor included as part of the MAC calculation:
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The Length to End (0008,0001) or any Tag with an element number of 0000 (i.e., no Data Set or group lengths may be included in MAC calculations)
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Tags with a group number less than 0008
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Tags associated with Data Elements whose VR is UN
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Tags of Data Elements whose VR is SQ, where any Data Element within that Sequence of Items has a VR of UN recursively
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Tags with a group number of FFFA (e.g., the Digital Signatures Sequence)
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MAC Parameters Sequence (4FFE,0001)
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Data Set Trailing Padding (FFFC,FFFC)
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Item Delimitation Item (FFFE,E00D)
Note
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The Length to End and group lengths can change if non-signed Data Elements change, so it is not appropriate to include them in the MAC calculation.
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Since the Data Element Tags that identify a Sequence and the start of each Item are included in the MAC calculation, there is no need to include the Item Delimitation Item Tags.
If any of the Data Element Tags in the list refer to a Sequence of Items, then the Tags of all Data Elements within all Items of that Sequence shall be implicitly included in the list of Data Elements Signed, except those disallowed above. This implicit list shall also include the Item Tag (FFFE,E000) Data Elements that separate the Sequence Items and the Sequence Delimitation Item (FFFE,E0DD).
Note
It is possible to sign individual Items within a Sequence by including the Digital Signatures Macro in that Sequence Item. In fact, this is a highly desirable feature, particular when used in the context of reports. The Digital Signatures Macro is applied at the Data Set level, and Sequences of Items are merely Data Sets embedded within a larger Data Set. Essentially, the Digital Signatures Macro may be applied recursively.
An example of nesting Digital Signatures within Data Elements is illustrated in Figure C.12-1.
Figure C.12-1. Example of Nesting Digital Signatures (Informative)
In this example, there is main signature covering the pixel data and a few other Data Elements, plus two individually signed Items within a Sequence.
For Data Elements with a VR OB (e. g. pixel data) that have an undefined length (i.e., the data is encapsulated as described in PS3.5), the Item Data Element Tags that separate the fragments shall implicitly be included in the list of Data Elements Signed (i.e., a Data Element with a VR of OB is encoded in the same fashion as a Sequence of Items).