POSER.md

Using Poser

The poser_gen and poser_verify tools can be used to prove possession of a secret key.

This is a bit of a mess as of this writing.

Generate a secret key:

hsmgen > sk.b32

Create a proof of possession signing request.

poser_gen $(hsmpk $(cat sk.b32)) i-own-this-key

This produces a lot of output, including a qrint (which looks like a very very long decimal number). Copy the coin id.

echo ~paste-coin-id~ > coin_id.hex

Then feed the qrint signature to hsms.

hsms -y sk.b32

then copy/paste the qrint decimal. Another qrint decimal will be output.

Convert signature to hex

These steps are ugly for now, sorry about that.

Copy to a qrint file.

echo ~paste-qrint-signature~ > sig.qr

Convert the qrint to binary

qrint sig.qr

Convert the binary to hex

python3 -c 'print(open("sig.qr.bin", "rb").read().hex())' > sig.hex

Verify the signature

poser_verify $(hsmpk $(cat sk.b32)) i-own-this-key $(cat coin_id.hex) $(cat sig.hex)

It should say message signed correctly.

Why do this?

These tools are used to prevent subtraction attacks, where two (or more) people agree to generate public keys and add them together to create a multi-sig key. The attacker goes last. The attacker generates a key K and subtracts the other key S (or the sum of the others keys if there is more than one other person) from it so the final sum is a public key the attacker knows. The attacker claims that his key is K-S, so the sum is K, which the attacker controls.