ISRG engaged the NCC Group Crypto Services team to perform a security review of Lets Encrypt’s certificate authority software, boulder, and the ACME protocol. The audit does not replace the WebTrust audit, which will happen after general availability of the service. NCC’s team was selected due to their strong reputation for cryptography expertise, which brought together Matasano Security, iSEC Partners, and Intrepidus Group. The audit is intended to provide additional assurance that our systems are secure.”]
Source: https://letsencrypt.org/2015/04/14/ncc-group-audit.html