He uses a unique initialization vector obtained from a cryptographically secure random number generator for each message, so there is no obvious issue with the

He uses a unique initialization vector obtained from a cryptographically secure random number generator for each message, so there is no obvious issue with the first block, too. UPDATE: Not entirely correct, see https://news.ycombinator.com/item?id=7400183 https://news.ycombinator.com/item?id=7400183.