serghey-rodin/vesta — pull request #124 by demlasjr (2014-03-18 23:40:16+00:00)
Title: Default DKIM keys with 1024-bit instead 512-bit

Seems like Google is not very happy with the 512-bit. There are many news and blogs posts about it.
Example: http://blog.wordtothewise.com/2012/11/gmail-sending-out-warnings-for-512-bit-dkim-keys/

I personally tested it with 1024-bit and 2048-bit and everything is working just fine.