Andrew Boyson / web

Common stuff for all my devices' web server pages: css, login, log, ipv4, ipv6, firmware update, clock, reset info etc.

Dependents:   oldheating gps motorhome heating

Security

A password has to be set whenever there has been a software reset. Resets following faults or power on do not require a new password as the hash is restored from the RTC GPREG register.

The password is not saved on the device; instead a 32 bit hash of the password is saved. It would take 2^31 attempts to brute force the password: this could be done in under a month if an attempt were possible every millisecond. To prevent this a 200 ms delay is introduced in the reply to the login form, that gives a more reasonable 13 years to brute force the password.

Once the password is accepted a random session id is created. This is 36 bit to give six base 64 characters but without an extra delay. If an attempt could be made every ms then this would still take over a year to brute force.

The most likely attack would to use a dictionary with, say, 10 million entries against the password which would still take 20 days to do.

login/http-login-session-id.c@71:d6aacc7d62ab, 2019-03-18 (annotated)

Committer:
andrewboyson
Date:
Mon Mar 18 11:23:09 2019 +0000
Revision:
71:d6aacc7d62ab
Child:
72:1ba60063c643
Tidied up the login module. In particular ensured that an empty sid could not be matched using a cookie with an empty value.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
andrewboyson 71:d6aacc7d62ab 1 #include <stdio.h>
andrewboyson 71:d6aacc7d62ab 2 #include <stdbool.h>
andrewboyson 71:d6aacc7d62ab 3
andrewboyson 71:d6aacc7d62ab 4 #include "clk.h"
andrewboyson 71:d6aacc7d62ab 5
andrewboyson 71:d6aacc7d62ab 6 #define GPREG4 (*((volatile unsigned *) 0x40024044)) //This is the battery backed GPREG2 address
andrewboyson 71:d6aacc7d62ab 7
andrewboyson 71:d6aacc7d62ab 8 static unsigned sessionId = 0; //This will be initialised to zero on startup
andrewboyson 71:d6aacc7d62ab 9 static char sessionIdString[9]; //Initialised to an empty string but will never be NULL.
andrewboyson 71:d6aacc7d62ab 10
andrewboyson 71:d6aacc7d62ab 11 static void makeSessionIdString()
andrewboyson 71:d6aacc7d62ab 12 {
andrewboyson 71:d6aacc7d62ab 13 sprintf(sessionIdString, "%08x", sessionId);
andrewboyson 71:d6aacc7d62ab 14 }
andrewboyson 71:d6aacc7d62ab 15 void HttpLoginSessionIdNew()
andrewboyson 71:d6aacc7d62ab 16 {
andrewboyson 71:d6aacc7d62ab 17 sessionId = ClkNowTai() & 0xFFFFFFFF;
andrewboyson 71:d6aacc7d62ab 18 makeSessionIdString();
andrewboyson 71:d6aacc7d62ab 19 GPREG4 = sessionId;
andrewboyson 71:d6aacc7d62ab 20 }
andrewboyson 71:d6aacc7d62ab 21 void HttpLoginSessionIdRestore()
andrewboyson 71:d6aacc7d62ab 22 {
andrewboyson 71:d6aacc7d62ab 23 sessionId = GPREG4;
andrewboyson 71:d6aacc7d62ab 24 makeSessionIdString();
andrewboyson 71:d6aacc7d62ab 25 }
andrewboyson 71:d6aacc7d62ab 26 bool HttpLoginSessionIdIsSet()
andrewboyson 71:d6aacc7d62ab 27 {
andrewboyson 71:d6aacc7d62ab 28 return sessionIdString[0];
andrewboyson 71:d6aacc7d62ab 29 }
andrewboyson 71:d6aacc7d62ab 30 char* HttpLoginSessionIdGet()
andrewboyson 71:d6aacc7d62ab 31 {
andrewboyson 71:d6aacc7d62ab 32 return sessionIdString;
andrewboyson 71:d6aacc7d62ab 33 }