> Hi Mz!

>

> Thanks for the article. But what’s the difference between the hash code and the control sum?

> As concern the file protection. It’s very rare that somebody tries to decipher the password or find out the algorithm you use to check if your file has been changed. Usually what you need is just to find the only command in your file:

>

> CMP (compare) &&if Ok then run application

>

> and mark it. That’s it :)

>

> Regards,

> Sergey

>

> PS I’ve read it in books about file protections.

Actually in some ways they are the same.

A checksum or CRC is usually used for Self Check or Self Test for Error Detection. For example:

a EAN13 Barcode has a checksum where the first 12 has a mathematical computation based on the Weight 131313131313.

In this way, it is easy to find out that the Barcode is valid or not.

Moreover, for data transmission in cellphones, the TCP/IP datagram, or other communication protocols, they include a

checksum in the end to confirm that the data sent was complete.

However, there are problems that arises to some CRC checking. Lets say we make a simple Checksum using SUM

thus if we have a number, given, 1234567 the checksum would be...

1 + 2 + 3 + 4 + 5 + 6 + 7 = 28 and we get the Remainder by **28 modulo 10** = **8**

Therefore, the data to be sent is 12345678 where 8 is the checksum. The problem in this kind of Checksum,

is that when we interchange the numbers. say 7654321, then we compute:

7 + 6 + 5 + 4 + 3 + 2 + 1 = 28 where the modulo is also equal to **8**

So whats the problem with this? The problem is that when we have a string say 'hello' the simple checksum is the

same for 'olleh' or 'helol'.

Because of that, there are new technologies and mathematical computation that arises and there comes the HASH.

The same results will also arise for a longer string of lets say 100MB of File. A 1 or 4 byte of CRC is not enough

for the accuracy of it... so far MD5 is the most reliable and secured HASH algorithm.

-Mz