How many bits of entropy can I expect from /dev/urandom in iOS?
I mailed Craig Federighi recently about this, concerned that macOS wasn’t capable of generating >128bit quality keys. 

He responded!


  “The source you were referencing is out of date.  You can find more current informations here:   FIPS certification document, section 7: "The NDRNG feeds entropy from the pool into the DRBG on demand.  The NDRNG provides 256-bits of entropy.””