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.

base/login/web-login-session-name.c

Committer:
andrewboyson
Date:
2019-07-31
Revision:
127:bd6dd135009d
Parent:
110:8ab752842d25

File content as of revision 127:bd6dd135009d:

#include "web-site-name.h"

#define SESSION_LIFE 10 * 365 * 24 * 60 * 60

//Do not use ' ', ';', '=' as they are part of the cookie protocol: name1=value1; name2=value2; name3=value3 etc
static char sessionName[9]; //Limit the name to 8 characters (plus terminating zero) to keep things quick

char* WebLoginSessionNameGet()
{
    return sessionName;
}

void WebLoginSessionNameCreate()
{
    //Make the session name from the site name - eg  "Heating" and "GPS Clock" will be "heat_sid" and "gpsc_sid"
    int i = 0;
    int j = 0;
    while (1)
    {
        if (i >= sizeof(sessionName) - 4 - 1) break; //Leave room for the "_sid" and the terminating NUL character
        char c = WEB_SITE_NAME[j++];
        if (!c) break;                               //Stop if run out of site name
        if (c >= 'A' && c <= 'Z') c |= 0x20;         //Make lower case
        if (c < 'a' || c > 'z') continue;            //Skip anything other than letters
        sessionName[i++] = c;                        //Add the first characters of the site name for which there is room
    }
    for (int k = 0; k < 4; k++)                      //Add "_sid"
    {
        sessionName[i++] = "_sid"[k];
    }
    sessionName[i] = 0;                              //Add the terminating NUL character
}

int WebLoginSessionNameLife()
{
    return SESSION_LIFE;
}