Obfuscation (software)

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In software development, obfuscation is the deliberate act of creating obfuscated code, i.e. source or machine code that is difficult for humans to understand.

Programmers may deliberately obfuscate code to conceal its purpose (security through obscurity) or its logic, in order to prevent tampering, deter reverse engineering, or as a puzzle or recreational challenge for someone reading the source code.

Programs known as obfuscators transform readable code into obfuscated code using various techniques.

Overview

The architecture and characteristics of some languages may make them easier to obfuscate than others.^[1]^[2] C,^[3] C++,^[4]^[5] and the Perl programming language^[6] are some examples of languages easy to obfuscate.

Recreational obfuscation

Writing and reading obfuscated source code can be a brain teaser for programmers. A number of programming contests reward the most creatively obfuscated code: the International Obfuscated C Code Contest, Obfuscated Perl Contest, and International Obfuscated Ruby Code Contest.

Types of obfuscations include simple keyword substitution, use or non-use of whitespace to create artistic effects, and self-generating or heavily compressed programs.

Short obfuscated Perl programs may be used in signatures of Perl programmers. These are JAPHs ("Just another Perl hacker").^[7]

Examples

This is a winning entry from the International Obfuscated C Code Contest^[8] written by Ian Phillipps in 1988^[9] and subsequently reverse engineered by Thomas Ball.^[10]

/*
  LEAST LIKELY TO COMPILE SUCCESSFULLY:
  Ian Phillipps, Cambridge Consultants Ltd., Cambridge, England
*/
 
#include <stdio.h>
main(t,_,a)
char
*
a;
{
	return!
 
0<t?
t<3?
 
main(-79,-13,a+
main(-87,1-_,
main(-86, 0, a+1 )
 
+a)):
 
1,
t<_?
main(t+1, _, a )
:3,
 
main ( -94, -27+t, a )
&&t == 2 ?_
<13 ?
 
main ( 2, _+1, "%s %d %d\n" )
 
:9:16:
t<0?
t<-72?
main( _, t,
"@n'+,#'/*{}w+/w#cdnr/+,{}r/*de}+,/*{*+,/w{%+,/w#q#n+,/#{l,+,/n{n+,/+#n+,/#;\
#q#n+,/+k#;*+,/'r :'d*'3,}{w+K w'K:'+}e#';dq#'l q#'+d'K#!/+k#;\
q#'r}eKK#}w'r}eKK{nl]'/#;#q#n'){)#}w'){){nl]'/+#n';d}rw' i;# ){nl]!/n{n#'; \
r{#w'r nc{nl]'/#{l,+'K {rw' iK{;[{nl]'/w#q#\
\
n'wk nw' iwk{KK{nl]!/w{%'l##w#' i; :{nl]'/*{q#'ld;r'}{nlwb!/*de}'c ;;\
{nl'-{}rw]'/+,}##'*}#nc,',#nw]'/+kd'+e}+;\
#'rdq#w! nr'/ ') }+}{rl#'{n' ')# }'+}##(!!/")
:
t<-50?
_==*a ?
putchar(31[a]):
 
main(-65,_,a+1)
:
main((*a == '/') + t, _, a + 1 )
:
 
0<t?
 
main ( 2, 2 , "%s")
:*a=='/'||
 
main(0,
 
main(-61,*a, "!ek;dc i@bK'(q)-[w]*%n+r3#l,{}:\nuwloca-O;m .vpbks,fxntdCeghiry")
 
,a+1);}

It is a C program that when compiled and run will generate the 12 verses of The 12 Days of Christmas. It contains all the strings required for the poem in an encoded form within the code.

A non-winning entry from the same year, the next example illustrates creative use of whitespace; it generates mazes of arbitrary length:^[11]

char*M,A,Z,E=40,J[40],T[40];main(C){for(*J=A=scanf(M="%d",&C);
--            E;             J[              E]             =T
[E   ]=  E)   printf("._");  for(;(A-=Z=!Z)  ||  (printf("\n|"
)    ,   A    =              39              ,C             --
)    ;   Z    ||    printf   (M   ))M[Z]=Z[A-(E   =A[J-Z])&&!C
&    A   ==             T[                                  A]
|6<<27<rand()||!C&!Z?J[T[E]=T[A]]=E,J[T[A]=A-Z]=A,"_.":" |"];}

Modern C compilers don't allow constant strings to be overwritten, which can be avoided by changing "*M" to "M[3]" and omitting "M=".

The following example by Óscar Toledo Gutiérrez, Best of Show entry in the 19th IOCCC, implements a 8080 emulator complete with terminal and disk controller, capable of booting CP/M-80 and running CP/M applications,^[12]

#include <stdio.h>
           #define n(o,p,e)=y=(z=a(e)%16 p x%16 p o,a(e)p x p o),h(
                                #define s 6[o]
             #define p z=l[d(9)]|l[d(9)+1]<<8,1<(9[o]+=2)||++8[o]
                                #define Q a(7)
           #define w 254>(9[o]-=2)||--8[o],l[d(9)]=z,l[1+d(9)]=z>>8
                               #define O )):((
                  #define b (y&1?~s:s)>>"\6\0\2\7"[y/2]&1?0:(
                               #define S )?(z-=
                    #define a(f)*((7&f)-6?&o[f&7]:&l[d(5)])
                               #define C S 5 S 3
                       #define D(E)x/8!=16+E&198+E*8!=x?
                             #define B(C)fclose((C))
                       #define q (c+=2,0[c-2]|1[c-2]<<8)
                          #define m x=64&x?*c++:a(x),
                         #define A(F)=fopen((F),"rb+")
                    unsigned char o[10],l[78114],*c=l,*k=l
                          #define d(e)o[e]+256*o[e-1]
#define h(l)s=l>>8&1|128&y|!(y&255)*64|16&z|2,y^=y>>4,y^=y<<2,y^=~y>>1,s|=y&4
+64506; e,V,v,u,x,y,z,Z; main(r,U)char**U;{
 
     { { { } } }       { { { } } }       { { { } } }       { { { } } }
    { { {   } } }     { { {   } } }     { { {   } } }     { { {   } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
    { { {   } } }    { { {     } } }    { { {   } } }    { { {     } } }
      { { ; } }      { { {     } } }      { { ; } }      { { {     } } }
    { { {   } } }    { { {     } } }    { { {   } } }    { { {     } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
   { { {     } } }   { { {     } } }   { { {     } } }   { { {     } } }
    { { {   } } }     { { {   } } }     { { {   } } }     { { {   } } }
     { { { } } }       { { { } } }       { { { } } }       { { { } } }
 
                                   for(v A((u A((e A((r-2?0:(V A(1[U])),"C")
),system("stty raw -echo min 0"),fread(l,78114,1,e),B(e),"B")),"A")); 118-(x
=*c++); (y=x/8%8,z=(x&199)-4 S 1 S 1 S 186 S 2 S 2 S 3 S 0,r=(y>5)*2+y,z=(x&
207)-1 S 2 S 6 S 2 S 182 S 4)?D(0)D(1)D(2)D(3)D(4)D(5)D(6)D(7)(z=x-2 C C C C
C C C C+129 S 6 S 4 S 6 S 8 S 8 S 6 S 2 S 2 S 12)?x/64-1?((0 O a(y)=a(x) O 9
[o]=a(5),8[o]=a(4) O 237==*c++?((int (*)())(2-*c++?fwrite:fread))(l+*k+1[k]*
256,128,1,(fseek(y=5[k]-1?u:v,((3[k]|4[k]<<8)<<7|2[k])<<7,Q=0),y)):0 O y=a(5
),z=a(4),a(5)=a(3),a(4)=a(2),a(3)=y,a(2)=z O c=l+d(5) O y=l[x=d(9)],z=l[++x]
,x[l]=a(4),l[--x]=a(5),a(5)=y,a(4)=z O 2-*c?Z||read(0,&Z,1),1&*c++?Q=Z,Z=0:(
Q=!!Z):(c++,Q=r=V?fgetc(V):-1,s=s&~1|r<0) O++c,write(1,&7[o],1) O z=c+2-l,w,
c=l+q O p,c=l+z O c=l+q O s^=1 O Q=q[l] O s|=1 O q[l]=Q O Q=~Q O a(5)=l[x=q]
,a(4)=l[++x] O s|=s&16|9<Q%16?Q+=6,16:0,z=s|=1&s|Q>159?Q+=96,1:0,y=Q,h(s<<8)
O l[x=q]=a(5),l[++x]=a(4) O x=Q%2,Q=Q/2+s%2*128,s=s&~1|x O Q=l[d(3)]O x=Q  /
128,Q=Q*2+s%2,s=s&~1|x O l[d(3)]=Q O s=s&~1|1&Q,Q=Q/2|Q<<7 O Q=l[d(1)]O s=~1
&s|Q>>7,Q=Q*2|Q>>7 O l[d(1)]=Q O m y n(0,-,7)y) O m z=0,y=Q|=x,h(y) O m z=0,
y=Q^=x,h(y) O m z=Q*2|2*x,y=Q&=x,h(y) O m Q n(s%2,-,7)y) O m Q n(0,-,7)y)  O
m Q n(s%2,+,7)y) O m Q n(0,+,7)y) O z=r-8?d(r+1):s|Q<<8,w O p,r-8?o[r+1]=z,r
[o]=z>>8:(s=~40&z|2,Q=z>>8) O r[o]--||--o[r-1]O a(5)=z=a(5)+r[o],a(4)=z=a(4)
+o[r-1]+z/256,s=~1&s|z>>8 O ++o[r+1]||r[o]++O o[r+1]=*c++,r[o]=*c++O z=c-l,w
,c=y*8+l O x=q,b z=c-l,w,c=l+x) O x=q,b c=l+x) O b p,c=l+z) O a(y)=*c++O r=y
,x=0,a(r)n(1,-,y)s<<8) O r=y,x=0,a(r)n(1,+,y)s<<8))));
system("stty cooked echo"); B((B((V?B(V):0,u)),v)); }

An example of a JAPH:

@P=split//,".URRUU\c8R";@d=split//,"\nrekcah xinU / lreP rehtona tsuJ";sub p{
@p{"r$p","u$p"}=(P,P);pipe"r$p","u$p";++$p;($q*=2)+=$f=!fork;map{$P=$P[$f^ord
($p{$_})&6];$p{$_}=/ ^$P/ix?$P:close$_}keys%p}p;p;p;p;p;map{$p{$_}=~/^[P.]/&&
close$_}%p;wait until$?;map{/^r/&&<$_>}%p;$_=$d[$q];sleep rand(2)if/\S/;print

This slowly displays the text "Just another Perl / Unix hacker", multiple characters at a time, with delays. An explanation can be found here.^[13]

Some Python examples can be found in the official Python programming FAQ.

Disadvantages of obfuscation

At best, obfuscation merely makes it time-consuming, but not impossible, to reverse engineer a program.^[14] In Java it also limits the use of the Reflection application programming interface on the obfuscated code.^[15] Some anti-virus software, such as AVG, will also alert their users when they land on a site with code obfuscated, as one of the purposes of obfuscation can be to hide malicious code. However, some developers may employ code obfuscation for the purpose of reducing file size or increasing security. The average user may not expect their antivirus software to provide alerts about an otherwise harmless piece of code, especially from trusted corporations, so such a feature may actually serve as a deterrent.

Obfuscating software

A variety of tools exists to perform or assist with code obfuscation. These include experimental research tools created by academics, hobbyist tools, commercial products written by professionals, and open-source software. ABCME is an obfuscation tool that assimilates assembly code to benign software codes.^[16] There also exist deobfuscation tools that attempt to perform the reverse transformation.

Although the majority of commercial obfuscation solutions work by transforming either program source code,^[17]^[18] or platform-independent bytecode as used by Java^[19] and .NET,^[20] there are also some that work with C and C++ - languages that are typically compiled to native code, or work directly on compiled binaries.

Obfuscation and copyleft licenses

There has been debate on whether it is illegal to skirt copyleft software licenses by releasing source code in obfuscated form, such as in cases in which the author is less willing to make the source code available. The general consensus was that while unethical, it was not considered a violation. The issue was clarified for the GNU General Public License when it was altered to require that the "preferred" version of the source code be made available.^[21]

Notes

↑ Binstock, Andrew (2003-03-06). "Obfuscation: Cloaking your Code from Prying Eyes". Web.archive.org. Retrieved 2013-11-25.
↑ Atwood, Jeff (2005-05-15). "Jeff Atwood, May 15 2005". Codinghorror.com. Retrieved 2013-11-25.
↑ "Obfuscation". Kenter.demon.nl. Retrieved 2013-11-25.
↑ "C++ Tutorials - Obfuscated Code - A Simple Introduction". DreamInCode.net. Retrieved 2013-11-25.
↑ "C Tutorials - Obfuscated Code in C". Sites.google.com. 2011-07-07. Retrieved 2013-11-25.
↑ As of 2013-11-25 18:22 GMT. "Pe(a)rls in line noise". Perlmonks.org. Retrieved 2013-11-25.
↑ http://rochester.pm.org/talks/japh_discussion.txt
↑ [The International Obfuscated C Code Contest]
↑ ""International Obfuscated C Code Winners 1988 - Least likely to compile successfully"". Ioccc.org. Retrieved 2013-11-25.
↑ ""Reverse Engineering the Twelve Days of Christmas" by Thomas Ball". Research.microsoft.com. Retrieved 2013-11-25.
↑ Don Libes, Obfuscated C and Other Mysteries, John Wiley & Sons, 1993, pp 425. ISBN 0-471-57805-3
↑ Óscar Toledo Gutiérrez: Intel 8080 emulator. 19th IOCCC. Best of Show.
↑ "Obfuscated Perl Program". Perl.plover.com. Retrieved 2013-11-25.
↑ ""Can We Obfuscate Programs?" by Boaz Barak". Math.ias.edu. Retrieved 2013-11-25.
↑ "Can I always use the Reflection API if the code is going to be obfuscated?". Stackoverflow.com. 2011-04-17. Retrieved 2013-11-25.
↑ Seyyedhamzeh, Javad, ABCME: A Novel Metamorphic Engine, 17th National Computer Conference, Sharif University, tehran, Iran, 2012
↑ "Open Directory - Computers: Programming: Languages: JavaScript: Tools: Obfuscators". Dmoz.org. 2013-08-03. Retrieved 2013-11-25.
↑ "Open Directory - Computers: Programming: Languages: PHP: Development Tools: Obfuscation and Encryption". Dmoz.org. 2013-09-19. Retrieved 2013-11-25.
↑ "Open Directory - Computers: Programming: Languages: Java: Development Tools: Obfuscators". Dmoz.org. 2013-04-09. Retrieved 2013-11-25.
↑ "Open Directory - Computers: Programming: Component Frameworks: .NET: Tools: Obfuscators". Dmoz.org. 2007-01-02. Retrieved 2013-11-25.
↑ "Reasoning behind the "preferred form" language in the GPL". Lwn.net. Retrieved 2013-11-25.

References

Seyyedhamzeh, Javad, ABCME: A Novel Metamorphic Engine, 17th National Computer Conference, Sharif University of Technology, Tehran, Iran, 2012.
B. Barak, O. Goldreich, R. Impagliazzo, S. Rudich, A. Sahai, S. Vadhan and K. Yang. "On the (Im)possibility of Obfuscating Programs". 21st Annual International Cryptology Conference, Santa Barbara, California, USA. Springer Verlag LNCS Volume 2139, 2001.
Mateas, Michael; Nick Montfort. "A Box, Darkly: Obfuscation, Weird Languages, and Code Aesthetics". Proceedings of the 6th Digital Arts and Culture Conference, IT University of Copenhagen, 1–3 December 2005. pp. 144–153. Cite uses deprecated parameters (help)

External links

The International Obfuscated C Code Contest
Protecting Java Code Via Code Obfuscation, ACM Crossroads, Spring 1998 issue
Protect Your Java Code - Through Obfuscators And Beyond, April 2009
Dotfuscator in Visual Studio on MSDN resource page — Visual Studio 2008 documentation for built-in .NET obfuscation
Obfuscation tools for .NET, on MSDN — Obfuscation resources for .NET, on the Microsoft Developer Center.
Can we obfuscate programs?
Yury Lifshits. Lecture Notes on Program Obfuscation (Spring'2005)
Java obfuscators on the Open Directory Project
Analysis of the 12 days program
Analysis of the obfuscated maze generating program
Obfuscated Perl program with explanation
Making C compiler generate obfuscated code
Analysis of javascript code obfuscation
Pseudo cycles insertion example
c2:BlackBoxComputation

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