encryption algorithm (urgent)

Posted on 2003-11-24
Medium Priority
Last Modified: 2010-04-17
yo im making my own (stream) encryption algorithm which is basically

for 0<=x<=length of text to be encrypted

text character(x) is xored by every pass character in turn

text character(x) is xored by the length of the entire password

text character(x) is xored by 1 pass character which rotates (i.e. the x th pass character mod the length of the password)

my problem is: if the password is longer than the text, the order of the excess of the password does not matter i.e.

text: ab
pass: 12345678

the incorrect pass: 12876543 will sucessfully decrypt the ciphertext :(

plz list ANY ideaz coz i really need to have this finished REALLY soon


Question by:suma_ds
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
LVL 22

Expert Comment

ID: 9815609
If the text to be encrypted is shorter than the key, why not pad the text out?

Or, consider the following.  So short a piece of plain text, in and of itself, should never carry much import, as a brute force and ignorance attack is quickly successful.  For example, not even the greenest security officer would every condone such a short, say, password for even the least userid.


Author Comment

ID: 9815705
ok i have tried padding the text but this does not increase security,  for example

text: abcd

pass: 12345678

padded text abcd0000

incorrect pass: 12348765

plaintext produced from decrypting with incorrect pass: abcdXXXX (X stands for any character)

this does not solve the problem coz it will be very obvious that the X's are just padding

LVL 22

Accepted Solution

cookre earned 500 total points
ID: 9815821
Hence the comment about little security for short plain text.

Now, if the recipient knows the good part is just, in this case, two bytes, and the cracker doesn't, padding with randomized instances of the plain text (e.g., abbbabaa) would make the crackers life a tad more difficult.

I wonder if you'd have the same problem with something like:

taking the stream in chunks of password length (padded if needed):

a <- chunk XOR password
a <- leftcircularshift(a,1)

a <- ak XOR password
a <- leftcircularshift(a,1)

a <- ak XOR password
a <- leftcircularshift(a,1)

with the decrypt being:

a <- rightcircularshift(chunk,1)
a <- a XOR password

a <- rightcircularshift(a,1)
a <- a XOR password

a <- rightcircularshift(a,1)
a <- a XOR password
LVL 84

Expert Comment

ID: 9815852
xoring with a password is a very weak encryption system even whenmodified to avoid the above problems
Here is a list of some stronger encryption algorithms

Author Comment

ID: 9816103
thankz cookre... that should work heaps good :)

Featured Post

Get 15 Days FREE Full-Featured Trial

Benefit from a mission critical IT monitoring with Monitis Premium or get it FREE for your entry level monitoring needs.
-Over 200,000 users
-More than 300,000 websites monitored
-Used in 197 countries
-Recommended by 98% of users

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Whether you’re a college noob or a soon-to-be pro, these tips are sure to help you in your journey to becoming a programming ninja and stand out from the crowd.
In this post we will learn different types of Android Layout and some basics of an Android App.
In this fifth video of the Xpdf series, we discuss and demonstrate the PDFdetach utility, which is able to list and, more importantly, extract attachments that are embedded in PDF files. It does this via a command line interface, making it suitable …
Starting up a Project

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question