Tk Library Source Code

Currently (as of version 0.7 of asn package) function asnGetContext  contain following check

   if {($tag & 0xE0) != 0x0a0} {
        return -code error \
            [format "Expected Context (0xa0), but got %02x" $tag]
   }

This check true if context-dependent tag has constructed encoding. However it is possible to have context-dependent tag with primitive encoding. For example, in PKCS7 format encrypted message data are stored as context-dependent tag with primitive encoding.

So, this check should be relaxed as 

  if {($tag & 0xC0) != 0x80} 

for more strict conformance with BER. It would be very nice to add additional optional parameter "encodingType" to asnGetContext, which would return value of 0x20 bit of the tag, thus letting application to know whether encoding of this tag was constructed or primitive.

Simular changes should be applied to asnGetApplication, which has the same problem.

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Fixed in asn 0.8.

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Agreed, that there is a problem with too strict checks in some places, there is also a RFE talking about a similar issue. I'll give it a bit more thought, as there are other issues like decoding CHOICE and SET structures, which is currently quite cumbersome, which would also need relaxed tag type checking and tag introspection to select the correct decoding (similar to the current string decoder).

File Added - 213235: asn.tcl.diff

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File Added: asn.tcl.diff