Solved

# Encrypt string and decrypt string

Posted on 2000-02-21
338 Views
Last Modified: 2012-05-04
Hi

i have value in edit box some i want to encrypt, and be able to decypt it again

Esk
0
Question by:esk
[X]
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14 Comments

LVL 2

Accepted Solution

aubs earned 100 total points
ID: 2543116
Why not just add an offset to each character in the edit box:

function encrypt(str: string):String;
var
i: integer;
begin
for i:= 1 to length(str) do
str[i]:= chr(ord(str[i]) + 100);
result:= str;
end;

function decrypt(str: string):String;
var
i: integer;
begin
for i:= 1 to length(str) do
str[i]:= chr(ord(str[i]) - 100);
result:= str;
end;

Here's another...

function EnDeCrypt(s:string): String;
var
i: integer;
begin
for i:= 1 to length(s) do
begin
if s[i]< '[' then //must be uppercase
s[i]:= chr(155 - ord(s[i]))
else
s[i]:= chr(219 - ord(s[i]));
end;
Result:= s;
end;

It can be used to encrypt and decrypt by simply swapping characters within the alphabet.
a to z,
b to y,
c to x,...
l to o,
m to n,
n to m,
o to l, etc. similarly for uppercase A to Z etc

155 = ASCII 'A' + ASCII 'Z'
219 = ASCII 'a' + ASCII 'z'

Aubs
0

LVL 6

Expert Comment

ID: 2543180
Esk : Have a look at my TEncrypt component...

http://www.freehomepages.com/secretdelphi/

(Suprised you didn't ask me about this in the 1st place!)

John.
0

LVL 6

Expert Comment

ID: 2543328
Just how secure do want this to be?
Do you have to worry about leaving un-encrypted values in ram/on disk?

GL
Mike
0

LVL 13

Expert Comment

ID: 2543369
0

LVL 17

Expert Comment

ID: 2543516
this was posted in another q some time ago. it is similar to aubs first comment :
using a random number up to 26 is used to offset each char. This way the string returned will always be readable, but much harder to decrypt because the offset is different every time.

You may want to alter the seed value, but there is no real advantage to this. MAKE SURE THE SEED IS THE SAME FOR ENCRYPTION AND DECRYTION!

function EncryptPassword(password: string): string;
var
i: integer;
begin
RandSeed:= 9999;
for i:= 1 to length(password) do
password[i]:= chr(ord(password[i]) + random(26));
Result:= Password;
end;

function DecryptPassword(s: string): string;
var
i: integer;
begin
s:='';
RandSeed:= 9999;
for i:= 1 to length(s) do
s[i]:= chr(ord(s[i]) - random(26));
Result:= s;
end;
0

LVL 13

Expert Comment

ID: 2543908
The 'cryptlib' I mentioned before is not the right one. This one is:

http://www3.ewebcity.com/joep/cryptlib.zip
0

LVL 3

Expert Comment

ID: 2544362
you can also use random chars up to 255 and then pass the number to HEX and to string, that way it's always readable also, but is double lenght than original
0

LVL 5

Expert Comment

ID: 2545418
esk,

It all depends what you want to do with the data. If you're going to encrypt the data into a file, and then decrypt it back when you read it out then there are better solutions than aubs. But if you actually want to encrypt the data as the user enters it then the code already supplied will do the job.

Bear in mind that aubs system isn't too complex of difficult to crack. Personally I'd go for a password overlay system. Basically it involves combining characters as ASCII values from a password. The encrypted text changes according to the password. It's not foolproof but is a little more advanced that what you've already been told.

If you want encryption and decryption routines for this then just ask

The Neil
0

LVL 8

Expert Comment

ID: 2546504
you can also use  Microsofts CryptoAPI

http://www.DelphiZine.com/features/1999/02/di199902mb_f/di199902mb_f.asp

Regards, Zif.
0

Author Comment

ID: 2550651
Jaymol, can you sent me demo at esk10000@hotmail.com

homesite did not work here!!!

Esk
0

Author Comment

ID: 2550672
aubs, your functions won't work
0

Author Comment

ID: 2550677
aubs, this works, my compiler was \$%/%&
0

LVL 2

Expert Comment

ID: 2550804
So does it work or does it not work?

Aubs
0

Author Comment

ID: 2551835
It works

thanks
Esk
0

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