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@80:9ea202546e7f, 2019-03-25 (annotated)

Committer:
andrewboyson
Date:
Mon Mar 25 10:24:29 2019 +0000
Revision:
80:9ea202546e7f
Parent:
79:e4cf94f9c9b2
Child:
81:4551f2e0e79b
Modified login to generate a 64 bit session id.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
andrewboyson 71:d6aacc7d62ab 1 #include <stdbool.h>
andrewboyson 79:e4cf94f9c9b2 2 #include <stdint.h>
andrewboyson 71:d6aacc7d62ab 3
andrewboyson 79:e4cf94f9c9b2 4 #include "random.h"
andrewboyson 71:d6aacc7d62ab 5
andrewboyson 80:9ea202546e7f 6 #define SESSION_ID_LENGTH 16 //Make sure this is no more than half the available random length
andrewboyson 71:d6aacc7d62ab 7
andrewboyson 80:9ea202546e7f 8 static char sessionIdString[SESSION_ID_LENGTH + 1]; //Initialised to an empty string but will never be NULL.
andrewboyson 80:9ea202546e7f 9
andrewboyson 71:d6aacc7d62ab 10 void HttpLoginSessionIdNew()
andrewboyson 71:d6aacc7d62ab 11 {
andrewboyson 80:9ea202546e7f 12 char* p = sessionIdString;
andrewboyson 80:9ea202546e7f 13
andrewboyson 80:9ea202546e7f 14 for (int i = 0; i < SESSION_ID_LENGTH / 2 && i < RANDOM_LENGTH; i++) //Don't exceed either random or sid lengths
andrewboyson 80:9ea202546e7f 15 {
andrewboyson 80:9ea202546e7f 16 int nibble;
andrewboyson 80:9ea202546e7f 17
andrewboyson 80:9ea202546e7f 18 nibble = RandomBytes[i] & 0x0F; //low nibble
andrewboyson 80:9ea202546e7f 19 *p++ = nibble < 10 ? nibble + '0': nibble - 0xA + 'a';
andrewboyson 80:9ea202546e7f 20
andrewboyson 80:9ea202546e7f 21 nibble = RandomBytes[i] >> 4; //high nibble
andrewboyson 80:9ea202546e7f 22 *p++ = nibble < 10 ? nibble + '0': nibble - 0xA + 'a';
andrewboyson 80:9ea202546e7f 23 }
andrewboyson 80:9ea202546e7f 24
andrewboyson 80:9ea202546e7f 25 *p = 0;
andrewboyson 71:d6aacc7d62ab 26 }
andrewboyson 71:d6aacc7d62ab 27 bool HttpLoginSessionIdIsSet()
andrewboyson 71:d6aacc7d62ab 28 {
andrewboyson 71:d6aacc7d62ab 29 return sessionIdString[0];
andrewboyson 71:d6aacc7d62ab 30 }
andrewboyson 71:d6aacc7d62ab 31 char* HttpLoginSessionIdGet()
andrewboyson 71:d6aacc7d62ab 32 {
andrewboyson 71:d6aacc7d62ab 33 return sessionIdString;
andrewboyson 71:d6aacc7d62ab 34 }