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-name.c@71:d6aacc7d62ab, 2019-03-18 (annotated)

Committer:
andrewboyson
Date:
Mon Mar 18 11:23:09 2019 +0000
Revision:
71:d6aacc7d62ab
Child:
82:980a393ff4dc
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 "page.h"
andrewboyson 71:d6aacc7d62ab 2
andrewboyson 71:d6aacc7d62ab 3 //Do not use ' ', ';', '=' as they are part of the cookie protocol: name1=value1; name2=value2; name3=value3 etc
andrewboyson 71:d6aacc7d62ab 4 static char sessionName[9]; //Limit the name to 8 characters (plus terminating zero) to keep things quick
andrewboyson 71:d6aacc7d62ab 5
andrewboyson 71:d6aacc7d62ab 6 char* HttpLoginSessionNameGet()
andrewboyson 71:d6aacc7d62ab 7 {
andrewboyson 71:d6aacc7d62ab 8 return sessionName;
andrewboyson 71:d6aacc7d62ab 9 }
andrewboyson 71:d6aacc7d62ab 10
andrewboyson 71:d6aacc7d62ab 11 void HttpLoginSessionNameCreate()
andrewboyson 71:d6aacc7d62ab 12 {
andrewboyson 71:d6aacc7d62ab 13 //Make the session name from the site name - eg "Heating" and "GPS Clock" will be "heat_sid" and "gpsc_sid"
andrewboyson 71:d6aacc7d62ab 14 int i = 0;
andrewboyson 71:d6aacc7d62ab 15 int j = 0;
andrewboyson 71:d6aacc7d62ab 16 while (1)
andrewboyson 71:d6aacc7d62ab 17 {
andrewboyson 71:d6aacc7d62ab 18 if (i >= sizeof(sessionName) - 4 - 1) break; //Leave room for the "_sid" and the terminating NUL character
andrewboyson 71:d6aacc7d62ab 19 char c = PageSite[j++];
andrewboyson 71:d6aacc7d62ab 20 if (!c) break; //Stop if run out of site name
andrewboyson 71:d6aacc7d62ab 21 if (c >= 'A' && c <= 'Z') c |= 0x20; //Make lower case
andrewboyson 71:d6aacc7d62ab 22 if (c < 'a' || c > 'z') continue; //Skip anything other than letters
andrewboyson 71:d6aacc7d62ab 23 sessionName[i++] = c; //Add the first characters of the site name for which there is room
andrewboyson 71:d6aacc7d62ab 24 }
andrewboyson 71:d6aacc7d62ab 25 for (int k = 0; k < 4; k++) //Add "_sid"
andrewboyson 71:d6aacc7d62ab 26 {
andrewboyson 71:d6aacc7d62ab 27 sessionName[i++] = "_sid"[k];
andrewboyson 71:d6aacc7d62ab 28 }
andrewboyson 71:d6aacc7d62ab 29 sessionName[i] = 0; //Add the terminating NUL character
andrewboyson 71:d6aacc7d62ab 30 }