I'm running a service that is using SHA-256 on two sides of the application - one is a server-side PHP implementation and the other is a client-side iOS implementation. The result of using the algorithm on both sides is the same alphanumeric string, except for the fact that all letters are capitalized on iOS and lower case on PHP. The fact that they are identical alphanumeric strings leads me to believe that SHA-256 is case insensitive, but I can't find any documentation supporting my assumption. Can someone show me some documentation to confirm this?
If you are referring to a hexadecimal string output, then yes, that is case insensitive. It is a textual representation of binary data.
http://en.wikipedia.org/wiki/Hexadecimal
The algorithm itself is most definitely case-sensitive.