Try google.

its not an answer !
GOOGLE is 2 vast.

I think Substitution chiper is good

Cryptography is based on algorithms (and some very heavy mathematical analysis), not choices of implementation language.
http://en.wikipedia.org/wiki/Cryptography

> I mean that can be acctualised using a C program.
Since C is a Turing complete language, if you have an algorithm, then you can express that algorithm in C.

> I think Substitution chiper is good
I look forward to emptying your bank account of all your money - as would any other person with even basic knowledge.

I look forward to emptying your bank account of all your money - as would any other person with even basic knowledge.

Substitution chiper can be made very strong by using many strings...

But since there is a definate pattern here (something is getting replaced or subsituted by something) it always is easy to crack to Substitution or Caesar Cipher. So it won't matter much no matter how long strings you use since there will always be a simple formula which the hacker will look for.

Chossing some tougher 64 bit or 128 bit algos which are commonly used nowadays would be a much better choice. Some of them are RSA (Rivest Shamir Adelman) , MD5 Hash algorithms etc.

i mean, it can be made stronger, if we...

choose the replacement for first character from first string,
for second from second string,
for third from third string, like this, say 10 times.
then again we will use first string, then second, and so on...

> choose the replacement for first character from first string,
> for second from second string,
So you're saying that if you have 4 strings as your key

that taking 't' 's' 'r' 'd' .... and the other 12 letters in some order, that the result is a lot more secure than using "thisismywordgrid" as the key?

Yeah, maybe it will fool a dictionary based attack, but it certainly doesn't fix any of the frequency analysis attacks (a problem faced by a lot of substitution cyphers). A good algorithm has to stand up to all known attack forms, not just those that can be done with pen and paper.

As for a chosen plaintext attack, that's just going to reveal the key straight off.

http://www.interhack.net/people/cmcu...e-oil-faq.html
Like has already been said, you need to spend a good long time doing lots of research on your own. Cryptography is a large and very technical subject. A brief Q&A on a message board isn't going to cut it.

substitution ciphers r really easy to decrypt be it in any complex form....
the best method is either using RSA ....
or any of the public key encryption methods (depending on the complexity of the host information, and how secure u want it to be)