[doc] added documentation

README.md

@@ -0,0 +1,36 @@
+libdecaf (goldilocks) based sphinx implementation
+
+sphinx is a cryptographic password storage as described in
+https://eprint.iacr.org/2015/1099
+
+sphinx has a very simple interface
+
+## step 1 - challenge
+the following creates a challenge for a device:
+```
+echo -n "shitty master password" | ../challenge >c 2>b
+```
+The master password is passed in through standard input.
+
+The challenge is sent to standard output.
+
+A blinding factor is stored in a tempfile, the name of this file is output to
+stderr. This tempfile is needed in the last step again.
+
+## step 2 - device responds
+Pass the challenge from step 1 on standard input like:
+```
+../respond secret <c >r0
+```
+The response is sent to standard output.
+
+## step 3 - derive password
+To derive a (currently hex) password, pass the response from step 2 on standard
+input and the filename of the tempfile from step 1 like:
+```
+fname=$(cat b)
+../derive $fname <r0 >pwd0
+```
+The derived password is sent to standard output and currently is a 32 byte
+binary string. Further transformations can be added which make it satisfy
+various character set requirements, this is todo ;)