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POHow to properly deobfusacte a Perl script?
 

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  1. POHow to properly deobfusacte a Perl script?
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    <p>I'm trying to deobfuscate the following Perl code (<a href="http://www.cafepress.co.uk/+just_another_genome_hacker_white_t,5065189">source</a>):</p> <pre><code>#!/usr/bin/perl (my$d=q[AA GTCAGTTCCT CGCTATGTA ACACACACCA TTTGTGAGT ATGTAACATA CTCGCTGGC TATGTCAGAC AGATTGATC GATCGATAGA ATGATAGATC GAACGAGTGA TAGATAGAGT GATAGATAGA GAGAGA GATAGAACGA TC GATAGAGAGA TAGATAGACA G ATCGAGAGAC AGATA GAACGACAGA TAGATAGAT TGAGTGATAG ACTGAGAGAT AGATAGATTG ATAGATAGAT AGATAGATAG ACTGATAGAT AGAGTGATAG ATAGAATGAG AGATAGACAG ACAGACAGAT AGATAGACAG AGAGACAGAT TGATAGATAG ATAGATAGAT TGATAGATAG AATGATAGAT AGATTGAGTG ACAGATCGAT AGAACCTTTCT CAGTAACAGT CTTTCTCGC TGGCTTGCTT TCTAA CAACCTTACT G ACTGCCTTTC TGAGATAGAT CGA TAGATAGATA GACAGAC AGATAGATAG ATAGAATGAC AGACAGAGAG ACAGAATGAT CGAGAGACAG ATAGATAGAT AGAATGATAG ACAGATAGAC AGATAGATAG ACAGACAGAT AGACAGACTG ATAGATAGAT AGATAGATAG AATGACAGAT CGATTGAATG ACAGATAGAT CGACAGATAG ATAGACAGAT AGAGTGATAG ATTGATCGAC TGATTGATAG ACTGATTGAT AGACAGATAG AGTGACAGAT CGACAGA TAGATAGATA GATA GATAGATAG ATAGACAGA G AGATAGATAG ACA GTCGCAAGTTC GCTCACA ])=~s/\s+//g;%a=map{chr $_=&gt;$i++}65,84,67, 71;$p=join$;,keys%a;while($d=~/([$p]{4})/g ){next if$j++%96&gt;=16;$c=0;for$d(0..3){$c+= $a{substr($1,$d,1)}*(4**$d)}$perl.=chr $c} eval $perl; </code></pre> <p>When run, it prints out <code>Just another genome hacker.</code> </p> <p>After running the code trough <code>Deparse</code> and <code>perltidy</code> (<code>perl -MO=Deparse jagh.pl | perltidy</code>) the code looks like this:</p> <pre><code>( my $d = "AA...GCTCACA\n" # snipped double helix part ) =~ s/\s+//g; (%a) = map( { chr $_, $i++; } 65, 84, 67, 71 ); $p = join( $;, keys %a ); while ( $d =~ /([$p]{4})/g ) { next if $j++ % 96 &gt;= 16; $c = 0; foreach $d ( 0 .. 3 ) { $c += $a{ substr $1, $d, 1 } * 4**$d; } $perl .= chr $c; } </code></pre> <p>Here's what I've been able to decipher on my own.</p> <pre><code>( my $d = "AA...GCTCACA\n" # snipped double helix part ) =~ s/\s+//g; </code></pre> <p>removes all whitespace in <code>$d</code> (the double helix).</p> <pre><code>(%a) = map( { chr $_, $i++; } 65, 84, 67, 71 ); </code></pre> <p>makes a hash with as keys <code>A</code>, <code>T</code>, <code>C</code> and <code>G</code> and as values <code>0</code>, <code>1</code>, <code>2</code> and <code>3</code>. I normally code in Python, so this translates to a dictionary <code>{'A': 0, 'B': 1, 'C': 2, 'D': 3}</code> in Python.</p> <pre><code>$p = join( $;, keys %a ); </code></pre> <p>joins the keys of the hash with <code>$;</code> the <a href="http://perldoc.perl.org/perlvar.html">subscript separator for multidimensional array emulation</a>. The documentation says that the default is "\034", the same as SUBSEP in awk, but when I do:</p> <pre><code>my @ascii = unpack("C*", $p); print @ascii[1]; </code></pre> <p>I get the value <code>28</code>? Also, it is not clear to me how this emulates a multidimensional array. Is <code>$p</code> now something like <code>[['A'], ['T'], ['C'], ['G']]</code> in Python?</p> <pre><code> while ( $d =~ /([$p]{4})/g ) { </code></pre> <p>As long as <code>$d</code> matches <code>([$p]{4})</code>, execute the code in the while block. but since I don't completely understand what structure <code>$p</code> is, i also have a hard time understanding what happens here.</p> <pre><code>next if $j++ % 96 &gt;= 16; </code></pre> <p>Continue if the the <code>$j</code> modulo 96 is greater or equal to 16. <code>$j</code> increments with each pass of the while loop (?).</p> <pre><code>$c = 0; foreach $d ( 0 .. 3 ) { $c += $a{ substr $1, $d, 1 } * 4**$d; } </code></pre> <p>For <code>$d</code> in the range from <code>0</code> to <code>3</code> extract some substring, but at this point I'm completely lost. The last few lines concatenate everything and evaluates the result.</p>
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    1. COAwesome question.
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      1. POHow to properly deobfusacte a Perl script?
      1. USRayfleck
    2. COYou should always be careful about code that `eval`s obfuscated strings. I've seen a devious question here on stackoverflow which ended with an eval of a string that turned out to be `"rm -rf /"`.
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    3. COReminds me of [Acme::EyeDrops](http://p3rl.org/Acme::EyeDrops).
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      1. POHow to properly deobfusacte a Perl script?
      1. USDavid Mertens
 

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