The ASCII form of the NCBI ASN.1 data does not follow any standard and is essentially an invention by NCBI (that's why they also provide some converters). Only the binary form can be processed with generic ASN.1 tools. BER is the standard low-level encoding used in binary ASN.1 and not, contrary to what you wrote, anything communication-specific. The standard approach to parse binary ASN.1 data is to get the encoding definition file for a specific downloadable item (they are provided by NCBI for all their ASN.1 data, which many definition parts shared between databases), generate a parser, and link that to your application.
I have done that for PubChem ASN.1 compound, substance, and assay data. I have been using the SNACC parser generator to generate C code for linking (warning: there are some data item sequences where SNACC generates wrong code, trying to read an extra token from the input stream. You need to postprocess the generated parser source to fix that). The assay and structure readers are components of the generic academic version of the Cactvs Cheminformatics Toolkit www.xemistry.com/academic) Also note that a parser is surprisingly large and complex do to extensive inclusion of definitions from other NCBI branches grown over decades. For example, the literature reference definition part included by the PubChem assay and structure data is much more extensive, with dozens of different ways to specify even the most exotic type of reference, than the actual structure and assay data part.