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Per Westermark
07/13/12 22:47
Read: 509 times
Sweden


 
#187931 - So what does the requirements spec say?
Responding to: ???'s previous message
Arif Deshmukh said:
Sine I am designing around PIC which has a built in EEPROM, so it also required to store a checksum/CRC byte to internal EEPROM or only four digit code sufficient?

Well - the difference between you and me is that it is you who are designing. So it must obviously be you who make the decisions what is sufficient or not. Unless you have a written requirements specification to fulfill.

In this system there will be two code, one is user code and second is master code. Both the codes are of four digits. If user code is forgotten then by master code person can open a safe.

It is really not smart to have a 4-digit master code. 4 digits represents a very small numeric range. And another thing is that having the master code 4 digits too means that a user who enters the 4 digit normal code and types wrong and opens the lock will have learned the master code. So an employee can, by accident, learn the master code. Which means that when the normal code is later changed, that user can still open the lock with the learned master code.

I want to know since PIC has a inbuilt EEPROM so still in this case checksum/CRC is necessary or without it.

Why do you think it is relevant if the EEPROM is internal or external?


List of 13 messages in thread
TopicAuthorDate
Password in EEPROM      Arif Deshmukh      07/13/12 17:29      
   Checksum      Per Westermark      07/13/12 21:29      
      8-digit code      Per Westermark      07/13/12 21:36      
         Master Code      Arif Deshmukh      07/13/12 22:35      
            So what does the requirements spec say?      Per Westermark      07/13/12 22:47      
            master codes ....      Erik Malund      07/14/12 01:12      
               This is a low-security lock - or no measly 4-digit PIN      Per Westermark      07/14/12 01:18      
                  language      Erik Malund      07/14/12 08:48      
                     just a thought      Erik Malund      07/14/12 09:09      
                        Never give access when locked      Per Westermark      07/14/12 10:14      
                     PIN + PUK      Per Westermark      07/14/12 10:11      
   The eeprom doesnt hold the password      Jez Smith      07/14/12 19:57      
      High/low security        Per Westermark      07/14/12 23:10      

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