The DGI encoding is specified in Annex B of the
"GlobalPlatform Systems Scripting Language Specification v1.1.0"
which is an "archived" specification that is no longer published
by GlobalPlatform, despite it being referenced from the GlobalPlatform
Card Specification v2.3, which is the basis of the GSMA eSIM
specifications.
For some reason it was the belief of the specification authors that
yet another format of TLV encoding is needed, in addition to the BER-TLV
and COMPREHENSION-TLV used by the very same specifications.
The encoding of the tag is not really specified anywhere, but I've only
seen 16-bit examples. The encoding of the length is specified and
implemented here accordingly.
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