Category: | Cryptography |
Author/Contact Info | Wombat |
Description: | I recognize that this is not a security group, but I figure there must be at least a few cypherpunks in the lot of you. I came up with this scheme for encrypting text, and submit it to you to see if anyone can come up with any obvious holes. The way this works, is a user types a passphrase which gets turned into a number between 0 and the maximum size of an integer (4,294,967,924). This number then is used to seed the random number generator. The program then collects single numbers between 0 and 7 by repeatedly calling rand(), until it has a bit vector. Then for each character of input, it maps the characters bits to the bit vector producing a scrambled character which it prints to STDOUT. By entering the same passphrase again, you get the same srand seed and thus can decrypt your bits at a later date. Features include: Arbitrarily long passphrases: Type as much as you like, the seed won't mind. Non-portability: (It's not a bug!) I realize that everyone has different random number generators. That's okay. I'm mostly using this to lock down my own personal secret files. I don't think the security would be compromised too much if a person sent the particulars of their random number generator along with cyphercode if they wanted a friend to get a message. No way to decrypt the text: I haven't coded the decryptor yet, so as of now, once encrypted, things STAY encrypted! :-) So yeah! Like, peer-review me and stuff! BTW: I do realize that this is "Weak security" at best, and probably can be defeated by brute force if so desired. I know. But BESIDES that... :-) ~W |
#!/usr/bin/perl -w $key=0; #Initialize variables. $updown=0; $i=0; @arrdone=(0,0,0,0,0,0,0,0); print "Enter passphrase: "; $phrase=<STDIN>; chomp $phrase; @letters = split //,$phrase; foreach $CHAR (@letters) { #Use phrase to create random seed $newbits=ord($CHAR); $modulo = $newbits % 10; if ($updown == 0) { if ($key < 0){$key*=-1;} $key=$key*($modulo+1); $key+=$newbits; if ($key>4294967294){$updown=1;} } if ($updown == 1) { $key=$key/($modulo+1)-($key%($modulo+1)/($modulo+1)); $key-=$newbits; if ($key<0){$updown=0;} } } srand $key; while(<STDIN>) { chomp; @inputchars = split //; foreach $CHAR (@inputchars){ $charnum=ord($CHAR); $oldt=$charnum; for (0..8) { #Translate the input char into binary $t = $charnum % (2**$_); if($t==$oldt) { $binarr[8-$_]=0; }else {$binarr[8-$_]=1;} $oldt=$t; } while ($i<8) { #Assemble the key bit vector. $randout=rand(8)%8; if ($arrdone[$randout]==0) { $shifter[$i]=$randout; $arrdone[$randout]=1; $i++; } } for(0..7) { #Assemble the scrambled bit vector. if ($binarr[$_]==1) { $outchar[$shifter[$_]] = 1; } else {$outchar[$shifter[$_]] =0;} } for(0..7) { #Rejoin the new bits to an ord if ($outchar[$_]==1) { $sum+=2**(7-$_); } } $och= chr($sum); #Print the char. print $och; $i=0; #Reset variables $sum=0; for(0..7){ $outchar[$_]=0; $arrdone[$_]=0; $shifter[$_]=0; } } } |
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