Hi all:

 

When encoding extension additions for a sequence type using the PER UNALIGNED variant, before the bitmap that indicates the presence or absence of extension additions for the sequence type being encoded, a length determinant needs to be added indicating the length of this bitmap. Therefore my question is the value that has to be encoded for the length determinant,

 

  1. Should indicate the number of extension additions (i.e if there are “n” extension additions for the type defined then the length determinant should be encoded to indicate “n”)?
  2. Or should indicate the number of extension additions – 1 (i.e if there are “n” extension additions for the type defined then the length determinant should be encoded to indicate “n-1”)?

 

The reason for this question is that I was looking at the bit patterns output by an ASN.1 tool and it was encoding the length determinant using the 2nd option that is mentioned above. The folks who maintain the tool pointed out that the length determinant has to indicate a number of at least one (see X.691, the note below 18.8) and hence the length can be normalized by subtracting one from it. Also if the second option is the correct way, can someone please point out where it is in the spec because I was following option 1 as this was what I got by reading clause 18.8. Any help is appreciated!

 

Thanks,

 

Chamira Perera


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