Schengen Visa Germany, sponsorship denied due to lack of “commitment form”

My Thai partner recently attended an appointment for a Schengen visa at the German embassy in Bangkok.

Upon arriving and before submitting the application we were informed the application would be denied because I lack a commitment of sponsorship form that I apparently would have to obtain from the German embassy in the UK, a form that before the appointment I have found no reference to on shengen Visa advice websites.

In the application I (as a UK citizen) provided a sponsorship letter detailing my commitment to pay the costs and explaining the source of my funds. For supporting documents I included up to date bank statements (coving more than 6 months from today’s date), proof of property ownership in the UK, a copy of my passport, and a fully booked (and paid for) itinerary for our trip to Europe.

We applied for and have had accepted a UK tourist visa having supplied much the same set documents.

I have evidence of considerably more than the recommended sufficient (£55x planned number of days) funds available going back long before the time period on my supplied bank statements.

We would be happy to adjust our itinerary to apply to a different Schengen country for the visa, ideally one we could apply to from within Thailand, countries which we are already planning to visit are: Germany, Czech Republic, Austria, Hungary, Romania.

If anybody has had experience with this situation could they suggest an alternative recourse for a Schengen visa application that would not require me to fly from Thailand to the the UK just to obtain a form?

how to transmit commitment transaction (unilateral close) from lightning network channel

How would you transmit a commitment transaction from a lightning network channel instead of closing the channel? I am working on implementing a watchtower and I first need to simulate a double spend attempt. When I close a channel with lmcli closechannel, both nodes have the bitcoin available and neither has to wait for the time lock. Is there a command to get the node to submit a unilateral close commitment transaction where one of them has to wait for the time lock?

Why is the obscured commitment number necessary in lightning commitment TX’s?

The obscured commitment number for each commitment transaction is the lower 48 bits of:

SHA256(payment_basepoint from open_channel || payment_basepoint from accept_channel) 

It is encoded in the lock time and sequence fields (24bits each) of the commitment transaction. I don’t understand why it is necessary, the BOLT rfc reads:

This obscures the number of commitments made on the channel in the case of unilateral close, yet still provides a useful index for both nodes (who know the payment_basepoints) to quickly find a revoked commitment transaction.

Why doesn’t the TXID of the commitment TX suffice as lookup index key?

Why is the privacy for using watch tower services increased with unpredictable commitment tx ids?

In the open channel message in BOLT 02 the following statement is written about the various basepoints.

The various _basepoint fields are used to derive unique keys as described in BOLT #3 for each commitment transaction. Varying these keys ensures that the transaction ID of each commitment transaction is unpredictable to an external observer, even if one commitment transaction is seen; this property is very useful for preserving privacy when outsourcing penalty transactions to third parties.

I wonder about the last sentence. Why does this in particular help with the privacy of such services? I thought I increase privacy by using several third party watching services and not only one. In case I use one they would know my entire channel state history anyway.

One thing that I guessed was that once I know one commitment tx I could calculate all txids for all possible channelstates. But I thought the signatures depend on the amount of the outputs and the txid depend on the signatures.

Do I have a misconception or is the reason for the increased privacy another one that I don’t see?

How can a find large primes for Pedersen commitment?

I want to make a commitment on Shamir’s Secret Sharing, based on the work of Pedersen, “Non-Interactive and Information-Theoretic Secure Verifiable Secret Sharing”.

To implement the commitment protocol, I need two primes q and p such that q | (p-1). How can one generate such primes?

Thanks in advance.

(Note: Might be more suitable for cryptograpy.stackexchange)