German legislation on use of qualified electronic signatures in contract law is in principle straightforward, as there is a rule that such a qualified electronic signature is equivalent to signing a document:
Soll die gesetzlich vorgeschriebene schriftliche Form durch die elektronische Form ersetzt werden, so muss der Aussteller der Erklärung dieser seinen Namen hinzufügen und das elektronische Dokument mit einer qualifizierten elektronischen Signatur nach dem Signaturgesetz versehen.
(§ 126a section (1) of the German Civil Code), or, in English:
If electronic form is to replace the written form prescribed by statute, the issuer of the declaration must add his name to it and provide the electronic document with a qualified electronic signature in accordance with the Electronic Signature Act.
But, apparently, the interesting question now is if I can insist on using a qualified electronic signature when I declare something (like inscribing at a university). This is not explicitly regulated in Germany in one way or another, so it is really open to some interpretation and it is a disputed question as of today. In such a situation, German lawyers tend to use the historic intentions of the legislative authorities to determine the scope of the respective rule, or to at least get near that scope.
§ 126a was added to the German Civil Code in 2001 and the German federal parliament discussed this rule before enacting it. Part of the documented discussion is this remark from the German federal government that was responsible for preparing the draft law:
In der Sache ist sich die Bundesregierung mit dem Bundesrat einig, dass niemandem gegen seinen Willen der elektronische Rechtsverkehr aufgezwungen werden darf.
(Source: BT-Drs. 41/4987, p. 41), or, in English:
The federal government agrees with the federal council that nobody may be forced against his will to participate in electronic legal relations.
This is an indication that one can only use a qualified electronic signature to declare something if the other involved party, may it be the recipient of the declaration or the contract partner, has agreed to this way of communication. However, as the law has no explicit rule, in the end only German courts could provide guidance by establishing relevant case law. Such case law is just not present in Germany so far here, I'm afraid.
My guess would be that German courts would follow the approach of the government that nobody must be forced to participate in electronic legal relations.