https://eprint.iacr.org/2019/779 https://eprint.iacr.org/2019/779 - Paper on the fun things you can do with signatures, including a write up of the Let's Encryp

https://eprint.iacr.org/2019/779 https://eprint.iacr.org/2019/779 - Paper on the fun things you can do with signatures, including a write up of the Let's Encrypt Attack discovered in 2015 and some more recent attacks.