On Fri, 30 Jan 2015 06:55:53 -0500, "devendra.aaru" said: > This is not caesar's cipher. If your buffer contains alphabets then only > you can apply caesar cipher. > > It should be something like > > encrypted[i] = (data[i] - 3) % 26; Consider the sequence of 4 hex bytes 0x17314B65. Your code will output that as 0x14141414. What happens when you try to decrypt that? Issue two: Your code fails to re-add an 'a' or 'A' as appropriate, so instead of rotating through ASCII hex codes 41-5A and 61-7A,it smashes then down to 0-19. If you're going that route, you need to go the *whole* way down that route: temp = data[i]; if (temp >= 'A' && temp <= 'Z') encrypted[i] = (temp -3) % 26 + 'A'; else if (temp >= 'a' && temp <= 'z') encrypted[i] = (temp -3) % 26 + 'a'; else encrypted[i] = temp; Moral of the story: Designing secure usable crypto is a *lot* harder than it looks. Also, I'm going to put in a plug for Bruce Schneier's 'Applied Cryptography, Second Edition' - a must-read if you're planning to do actual crypto work.
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