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@79:e4cf94f9c9b2, 2019-03-24 (annotated)

Committer:
andrewboyson
Date:
Sun Mar 24 19:42:41 2019 +0000
Revision:
79:e4cf94f9c9b2
Parent:
76:bb34dbb26aae
Child:
80:9ea202546e7f
Modified the session id in login to use a 64 bit random number from the new random module; the previous 32bit number was probably not long enough to preclude brute forcing the sid.

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 79:e4cf94f9c9b2 3 #include <stdint.h>
andrewboyson 71:d6aacc7d62ab 4
andrewboyson 71:d6aacc7d62ab 5 #include "clk.h"
andrewboyson 79:e4cf94f9c9b2 6 #include "random.h"
andrewboyson 71:d6aacc7d62ab 7
andrewboyson 79:e4cf94f9c9b2 8 static uint64_t sessionId = 0; //This will be initialised to zero on startup
andrewboyson 79:e4cf94f9c9b2 9 static char sessionIdString[17]; //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 79:e4cf94f9c9b2 13 sprintf(sessionIdString, "%016llx", sessionId);
andrewboyson 71:d6aacc7d62ab 14 }
andrewboyson 71:d6aacc7d62ab 15 void HttpLoginSessionIdNew()
andrewboyson 71:d6aacc7d62ab 16 {
andrewboyson 79:e4cf94f9c9b2 17 sessionId = Random64;
andrewboyson 71:d6aacc7d62ab 18 makeSessionIdString();
andrewboyson 71:d6aacc7d62ab 19 }
andrewboyson 71:d6aacc7d62ab 20 bool HttpLoginSessionIdIsSet()
andrewboyson 71:d6aacc7d62ab 21 {
andrewboyson 71:d6aacc7d62ab 22 return sessionIdString[0];
andrewboyson 71:d6aacc7d62ab 23 }
andrewboyson 71:d6aacc7d62ab 24 char* HttpLoginSessionIdGet()
andrewboyson 71:d6aacc7d62ab 25 {
andrewboyson 71:d6aacc7d62ab 26 return sessionIdString;
andrewboyson 71:d6aacc7d62ab 27 }