Introducing Google Cloud Key Management Service
cloudplatform.googleblog.com
cloudplatform.googleblog.com
Cloud KMS doesn't implement an open standard (there aren't a number of good open standards in the space, KMIP is probably the only candidate I'm familiar with), but use of the current functionality shouldn't be very hard to port to some other API. (Although, given the dependency on keys, etc., this may not apply to moving any reposed data, that's fundamentally more challenging.)
[repeated disclaimer: I work on the product]