On the ANTLR web site, http://www.antlr.org/grammar/list, there is a contribution of an ASN1 parser. http://www.antlr.org/grammar/1068589793853/ASN1_grammar.zip. It has your name but, there is no email contact. Did you contribute this parser?
If it is you, what is the licensing on your parser? We would like to use your ASN1 parser for our Apache Directory project and hope that it is compatible with Apache Software Foundation licensing guidelines, http://www.apache.org/licenses.