GEIER is the first free library to encrypt, digitally sign, decrypt, validate and send gathered tax declarations data to the German inland revenue offices. Furthermore it allows to generate XHTML transmission protocols using XSLT mechanisms.

GEIER is short for GPL'd Elster Interface and part of the Taxbird project.

GEIER uses the COALA interface supplied by the German inland revenue offices. COALA is a publicly documented transmission interface, which heavily relies on XML. The data is transmitted compressed with GZIP and symmetrically encrypted with a 3DES key. The 3DES key, which is generated by the GEIER library, is sent to the Elster servers after it has been asymmetrically encrypted using the RSA algorithm. For the actual transmission HTTP/Post is utilized.

Besides plain transmission GEIER is capable of digitally signing the Elster XML-documents using software certificates (X.509 based). The latter approach is called Elster Basis by the fiscal authorities.

Please mind, that GEIER heavily relies on Mozilla (xulrunner) NSS.