1. Data Encryption
- Posted by Bryan Watts <mr_bungle at COMPUSERVE.COM>
May 14, 1998
-
Last edited May 15, 1998
To all you Euphorians out there,
I have recently gotten into data encryption algorithms, and just to
see, I have developed a *very* basic one, implemented into
the program at the end of this letter. I can get a sentence
encrypted and decrypted fine, and I can also encrypt a file
as well. My problem is that when I try to decrypt the file,
sometimes the marker that shows which bit to switch in
the character ("ch" in the "decrypt_file" procedure)
sometimes reads in a very strange value, and causes a
subscript error. It happens randomly, sometimes not at all,
and it has me completely baffled. I think this would be a
very cool program, and useful too, if I could get it to run!!
Any help as to what may be causing this weird error would
be greatly appreciated!! Thanks a lot.
Regards,
Bryan Watts
(Oh yeah, I'm a junior in high school, and while it may
not seem like much to you guys, my team came in 4th place
out of 40 teams in the SouthWest US in a computer
programming contest at UCF. Yay me!)
----------- Encrypt.ex starts here ----------------
include get.e
with trace
function ch_to_bits(integer ch) --changes a character to bits
integer num2
sequence bits
bits =3D repeat(0,8)
num2 =3D 128
for i =3D 1 to 8 do
if ch - num2 < 0 then
bits[i] =3D '0'
else
bits[i] =3D '1'
end if
if bits[i] =3D '1' then
ch =3D ch - num2
end if
if i !=3D 8 then
num2 =3D num2 / 2
end if
end for
return bits
end function
function bits_to_ch(sequence bits) --changes bits to a character
integer num2,final
num2 =3D 128
final =3D 0
for i =3D 1 to 8 do
if bits[i] =3D '1' then
final =3D final + num2
end if
if i !=3D 8 then
num2 =3D num2 / 2
end if
end for
return final
end function
function encrypt(integer ch) =
integer x
sequence bits
x =3D rand(8) --select a random number...
bits =3D ch_to_bits(ch)
bits[x] =3D (1 - (bits[x] - '0')) + '0' --...and switch that element's=
bit
ch =3D bits_to_ch(bits)
return {x,ch} --return {element changed,new random character}
end function
function decrypt(sequence encrypted) --a sequence of {bit switched,new
character}
integer ch
sequence bits
bits =3D ch_to_bits(encrypted[2])
bits[encrypted[1]] =3D (1-(bits[encrypted[1]] - '0')) + '0' --switch
original bit back
ch =3D bits_to_ch(bits)
return ch
end function
procedure encrypt_file() --self-explanatory
integer ch,filenum,done,filenum2
sequence file,dummy
done =3D 0
puts(1,"Enter the file name now: ")
file =3D gets(0)
position(17,30)
file =3D file[1..length(file)-1]
filenum =3D open(file,"r")
if filenum =3D -1 then
printf(1,"Cannot open \"%s\"",{file})
ch =3D wait_key()
else
filenum2 =3D open(file,"w")
while not done do
ch =3D getc(filenum)
if ch =3D -1 then
done =3D 1
elsif ch =3D '\n' then
puts(filenum2,ch)
else
dummy =3D encrypt(ch)
printf(filenum2,"%s%s",{dummy[1],dummy[2]})
end if
end while
close(filenum)
close(filenum2)
puts(1,"Your file has been encrypted.")
ch =3D wait_key()
end if
end procedure
=
procedure decrypt_file()
sequence file,dummy2
integer done,filenum,filenum2,dummy,ch2,ch
done =3D 0
puts(1,"Enter the filename now: ")
file =3D gets(0)
position(17,30)
dummy2 =3D ""
file =3D file[1..length(file)-1]
filenum =3D open(file,"r")
if filenum =3D -1 then
printf(1,"Cannot open \"%s\"",{file})
else
filenum2 =3D open(file,"w")
--trace(1)
while not done do
ch =3D getc(filenum) --here is where the error occurs. It should
always be in [1..8]
if ch =3D -1 then
done =3D 1
elsif ch =3D '\n' then
puts(filenum2,ch)
else
ch2 =3D getc(filenum)
dummy =3D decrypt({ch,ch2})
dummy2 =3D dummy2 & dummy --debug help, ignore
puts(filenum2,dummy)
end if
end while
close(filenum)
close(filenum2)
puts(1,"Your file has been decrypted.")
done =3D wait_key()
end if
end procedure
procedure main()
sequence choices
integer ch,done
done =3D 0
choices =3D {"Encrypt a file","Decrypt a file","Quit"}
while not done do
clear_screen()
for i =3D 1 to 3 do
position(10+i,30)
printf(1,"%d: %s",{i,choices[i]})
end for
ch =3D wait_key()
position(15,30)
if ch =3D '1' then
encrypt_file()
elsif ch =3D '2' then
decrypt_file()
elsif ch =3D '3' then
done =3D 1
end if
end while =
end procedure
main()
2. Re: Data Encryption
I haven't tested it, but I already found a logical adjustment tha prolly
made the bug occur.
When you open a file normally, after every '\n' a value of 10 (ascII 10)
gets placed, so your file obbeys to the ASCII text format. When you read in
however, only gets () removes such a character again. And even if getc ()
also did that (I dunno.. I don't think so) there would still be the case
where you yourself put a value of 10 to the value (due to encrypting or
whatever) but when you read the file back, it gets eliminated. To avoid
this.. open such files as binairy. Thus with the option flags: "wb" to write
and "rb" to read.
Furthermore I've shorten some of your code.. and the '!' means, the line has
to replaced with the next line.
You're welcome.
Ralf Nieuwenhuijen
nieuwen at xs4all.nl
>----------- Encrypt.ex starts here ----------------
>
>include get.e
include machine.e -- int_to_bits () and bits_to_int ()
>function ch_to_bits(integer ch) --changes a character to bits
-- Be warned it returns its values in reversed order!!
return int_to_bits (ch,8)
>end function
>function bits_to_ch(sequence bits) --changes bits to a character
return bits_to_int (bits)
>end function
>function encrypt(integer ch)
> integer x
> sequence bits
> x = rand(8) --select a random number...
> bits = ch_to_bits(ch)
X bits[x] = (1 - (bits[x] - '0')) + '0' --...and switch that element's bit
bits[x] = not bits[x]
-- we no longer use '0' but real FALSE value and real TRUE value
> ch = bits_to_ch(bits)
> return {x,ch} --return {element changed,new random character}
>end function
>function decrypt(sequence encrypted) --a sequence of {bit switched,new
>character}
> integer ch
> sequence bits
> bits = ch_to_bits(encrypted[2])
! bits[encrypted[1]] = (1-(bits[encrypted[1]] - '0')) + '0' --switch
bits[encrypted[1]] = not bits[encrypted[1]]
> ch = bits_to_ch(bits)
> return ch
>end function
>
>procedure encrypt_file() --self-explanatory
> integer ch,filenum,done,filenum2
> sequence file,dummy
> done = 0
> puts(1,"Enter the file name now: ")
> file = gets(0)
> position(17,30)
> file = file[1..length(file)-1]
> filenum = open(file,"r")
> if filenum = -1 then
> printf(1,"Cannot open \"%s\"",{file})
> ch = wait_key()
> else
! filenum2 = open(file,"w")
filenum2 = open(file, "wb")
> while not done do
> ch = getc(filenum)
> if ch = -1 then
> done = 1
> elsif ch = '\n' then
> puts(filenum2,ch)
> else
> dummy = encrypt(ch)
> printf(filenum2,"%s%s",{dummy[1],dummy[2]})
> end if
> end while
> close(filenum)
> close(filenum2)
> puts(1,"Your file has been encrypted.")
> ch = wait_key()
> end if
>end procedure
>
>procedure decrypt_file()
> sequence file,dummy2
> integer done,filenum,filenum2,dummy,ch2,ch
> done = 0
> puts(1,"Enter the filename now: ")
> file = gets(0)
> position(17,30)
> dummy2 = ""
> file = file[1..length(file)-1]
! filenum = open(file,"r")
filenum = open(file, "rb")
> if filenum = -1 then
> printf(1,"Cannot open \"%s\"",{file})
> else
> filenum2 = open(file,"w")
> --trace(1)
> while not done do
> ch = getc(filenum) --here is where the error occurs. It should
>always be in [1..8]
> if ch = -1 then
> done = 1
> elsif ch = '\n' then
> puts(filenum2,ch)
> else
> ch2 = getc(filenum)
> dummy = decrypt({ch,ch2})
> dummy2 = dummy2 & dummy --debug help, ignore
> puts(filenum2,dummy)
> end if
> end while
> close(filenum)
> close(filenum2)
> puts(1,"Your file has been decrypted.")
> done = wait_key()
> end if
>end procedure
>
>procedure main()
> sequence choices
> integer ch,done
> done = 0
> choices = {"Encrypt a file","Decrypt a file","Quit"}
> while not done do
> clear_screen()
> for i = 1 to 3 do
> position(10+i,30)
> printf(1,"%d: %s",{i,choices[i]})
> end for
> ch = wait_key()
> position(15,30)
> if ch = '1' then
> encrypt_file()
> elsif ch = '2' then
> decrypt_file()
> elsif ch = '3' then
> done = 1
> end if
> end while
>end procedure
>
>main()
3. Re: Data Encryption
I think your method could be duplicated with a simple xor function. a crude
example follows.
note that in this example multiple bits are switched out rather than just one
------------------------encrypt.ex:
include machine.e
include get.e
sequence filein, fileout, buffer, ext
atom key,char,stroke,done
puts(1,"enter file to encrypt: ")
filein={"",0}
done=0
while 1 do
stroke=wait_key()
if stroke!=13 then
puts(1,{stroke})
filein[1]=filein[1]&stroke
else
exit
end if
end while
filein[2]=open(filein[1],"r")
if filein[2]=-1 then
puts(1,"invalid file name")
stroke=wait_key()
abort(0)
end if
fileout={"",0}
for p=1 to length(filein[1]) do
if filein[1][p]='.' then
fileout[1]=filein[1][1..p]&"hid"
ext=filein[1][p+1..length(filein[1])]
exit
elsif p=length(filein[1]) then
fileout[1]=filein[1][1..p]&".hid"
ext={}
end if
end for
fileout[2]=open(fileout[1],"w")
key=rand(255)
buffer={key}&length(ext)&ext
while 1 do
char=getc(filein[2])
if char=-1 then
exit
elsif char='\n' then
buffer=buffer&'\n'
else
buffer=buffer&xor_bits(key,char)
end if
end while
puts(fileout[2],buffer)
close(filein[2])
close(fileout[2])
---------------------------------decrypt.ex:
include machine.e
include get.e
sequence filein, fileout, buffer, ext
atom key,char,stroke
puts(1,"enter file to decrypt: ")
filein={"",0}
while 1 do
stroke=wait_key()
if stroke !=13 then
puts(1,{stroke})
filein[1]=filein[1]&stroke
else
exit
end if
end while
filein[2]=open(filein[1],"r")
if filein[2]=-1 then
puts(1,"invalid file name")
stroke=wait_key()
abort(0)
end if
key=getc(filein[2])
char=getc(filein[2])
ext={}
if char>0 then
ext="."
for p=1 to char do
ext=ext&getc(filein[2])
end for
end if
fileout={filein[1][1..length(filein[1])-4]&ext,0}
fileout[2]=open(fileout[1],"w")
buffer={}
while 1 do
char=getc(filein[2])
if char=-1 then
exit
elsif char='\n' then
buffer=buffer&'\n'
else
buffer=buffer&xor_bits(key,char)
end if
end while
puts(fileout[2],buffer)
close(filein[2])
close(fileout[2])
4. Re: Data Encryption
>I have recently gotten into data encryption algorithms, and just to
>see, I have developed a *very* basic one, implemented into
>the program at the end of this letter. I can get a sentence
>encrypted and decrypted fine, and I can also encrypt a file
>as well. My problem is that when I try to decrypt the file,
>sometimes the marker that shows which bit to switch in
>the character ("ch" in the "decrypt_file" procedure)
>sometimes reads in a very strange value, and causes a
>subscript error. It happens randomly, sometimes not at all,
>and it has me completely baffled. I think this would be a
>very cool program, and useful too, if I could get it to run!!
>Any help as to what may be causing this weird error would
>be greatly appreciated!! Thanks a lot.
I'll take a look at it. I have made one that uses password encryption. I
figure that if you use several passwords, and decrypt with the WRONG
password at least once, the file would be impossible to crack, especially
if I make a couple of changes to the basic algorithm. It's fast too.
This is how mine works:
It gets and confirms the password
It performs calculations on the password (adding the ASCII values up and
such and a little bit more) to get a number.
Seeds the randomizer to the number (set_rand(number))
Takes each character in the file, and adds a random number between 1 and
255 to it and puts it into the output file. (or subtracts in decryption)
Since it seeds the randomizer, the rand() results will always be the same
for each different password, but you have to know the password (or at
least a password that would give you the same number) in order to decrypt
it. (And you will need the program if I change a little bit that happens
in the main loop, since you won't know exactly what the formula is)
> (Oh yeah, I'm a junior in high school, and while it may
> not seem like much to you guys, my team came in 4th place
> out of 40 teams in the SouthWest US in a computer
> programming contest at UCF. Yay me!)
Cool! That's a lot of competition. I got 1st at the C++ at the Great
Computer Challenge at ODU (i'm a senior in high school :).. But there
were only 5 total teams. The coolest part was beating New Horizons
Government School, who had won the last 3 years. They had 5 people on
their team. We had two, and it was our first time. :) We finished all
four programs (we weren't supposed to have enough time to do that.... :),
and 3 of them had a few bugs (not glitches! :) and grammar errors...
Imagine how well we could have done if we could have used Euphoria! ;)
(We did have Windows NT, so that sorta provided at least some subscript
checking for us....)
I recreated each program in about an hour, I think, in Euphoria at home.
Although I did know what we did and all after then, but I know we could
have done even better with Euphoria.. :)
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5. Re: Data Encryption
I too am a member of the encryption club (it is a relatively simple thing to
code). There are a couple of things I would like to add, the first is the
power of matrix encryption. This makes the messed up file completely
indistinguishable from the original, as the bytes no longer correspond. The
second is rot (rotate) type encryption. The usefullness of this is that you
can encode a text file and it will still be text. This allows you to paste it
straight into an email (rather than using something like BinHex or Base64). Of
course you could BinHex a Matrix encrypted file, but I find that a bit cheesy.
I have not perfected the rot part of my alg. It works but would still be no
good for email (ASCII values > 128). I have got the necessary Matrix code if
anybody wants it. (Multiply, Calculate Inverse, Determinate).
"School was brought in to impart on our children a new understanding. An
understanding so new that nobody has even discovered yet." - Les Mailles
Daniel
6. Re: Data Encryption
Salutations,
>I have recently gotten into data encryption algorithms, and just to
>see, I have developed a *very* basic one,
Not as "basic" as the one I did. Rather than manipulate the characters
on a binary level, I just added a certain integer to each ascii code and
if it ened up more than 256 then I subtracted 256 from it or something
like that.
>as well. My problem is that when I try to decrypt the file,
>sometimes the marker that shows which bit to switch in
>the character ("ch" in the "decrypt_file" procedure)
>sometimes reads in a very strange value, and causes a
>subscript error.
Like some one else said, watch out for the "\n" character.
I didn't have to worry about that in my prog.
It happens randomly, sometimes not at all,
>and it has me completely baffled. I think this would be a
>very cool program, and useful too, if I could get it to run!!
Yes it would, keep working on it. You'll figure it out.
If you want to check my proggie out it is on the recent user
contributions page in the "graphics bundle" by Lewis Townsend :)
It works for both typing and text files as long as the characters are
within 256 chars :)
> Bryan Watts
> (Oh yeah, I'm a junior in high school, and while it may
> not seem like much to you guys, my team came in 4th place
> out of 40 teams in the SouthWest US in a computer
> programming contest at UCF. Yay me!)
Cool, I wish my high school would have participated in cool contests
like that. I guess I was lucky to have been in art contests they were
fun and sometimes we got to go outside and draw :)
Sincerely,
Lewis Townsend
|\ ____ _ _ _ _ __
| \ | __/ || / | // || / __ \
| \ ||_ || //|| // || ||__\|
| \ | _| || // || // || \___ \
| |\ \ ||__ ||// ||// || |\__||
| | \ \|___\ |_/ |_/ || \____/
| | \ \ _____ ________
| | \ \ | __ \ | __ __ |
| | \ \ ||__|| |/ || \|
| | \ \ | __ / ||
| |______\ \ || \\ ||
|___________\ || || ||
Keroltarr at hotmail.com
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7. Re: Data Encryption
Thank you to all who helped me out. I'm still getting that
same bug, though!! Ralf, I tried your suggestion of "rb"
instead of "r", but the error keeps occurring. And, I know about
the "int_to_bits" and "bits_to_int" and "not_bits" functions,
but I originally started this program in Pascal for school,
which does not have those functions. Therefore, I figured
them out myself, and implemented them in this code to make
sure they worked, which they do. I just don't understand it...
Isn't technology wonderful? 
Well, I'll continue to work on it,
and if anyone has given this a test run, maybe fill me in?
I'd appreciate any help!! Thanks for your time!
Regards,
Bryan Watts
8. Re: Data Encryption
I did an encrypter a while back.
It does the following.
1) Expands the code into a 256 "ramdom" character string
2) Loads and encrypts data from files in blocks
3) The exact length of the blocks is determined by a
checksum derived from the code string
4) Starts encrypting at a derived point in each block
XORing each byte with a character from the code
string and a number from rand() and the value of the
next byte *before* it is in turn encrypted (except
for the 'last' byte, which could be any byte in the
block) It continues encrypting forward until the end
of the block then starts from the beginning of the
block and works up to the 'first' byte
Reasonable security at 15MB per minute, re-writing the
output to a seperate file (P-120)
Graeme
----------------------------------------
Got to do one of those signiture thingys
----------------------------------------
9. Re: Data Encryption
I did one of these ages ago. I ported it from Qbasic to a language called
"MoonRock", and then to Euphoria, but I can't think why the source isn't
on my web page.
The .COM file produced by MoonRock is lurking on my DOS webpage under the
heading ENCODE v1.1. It even comes with documentation (which happens to
be longer than the .COM file). It's a piece of my coding history, 'cause
it's still got my old "company" name (CresSoft) in it!
Mental note: Upgrade it before the real CresSoft get a hold of me!
I'll post to the list when I put the Euphoria source (which is probably
very similar to one I've already seen in this thread) in my web Euphoria
directory.
--
Carl R White
E-mail...: cyrek- at -bigfoot.com / Remove the hyphens before
Finger...: crwhite- at -dcsun1.comp.brad.ac.uk \ mailing or fingering...
Url......: http://www.bigfoot.com/~cyrek/
