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Obfuscation (software)

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.

Contents

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]:&am p;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& amp;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 CC 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)  Om 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.

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.[13] In Java it also limits the use of the Reflection application programming interface on the obfuscated code.[14] 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. This however, can be a quick deterrent to most people, who do not expect a professional site to be flagged up by their anti-virus software.[clarification needed]

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.[15] 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,[16][17] or platform-independent bytecode as used by Java[18] and .NET,[19][20] there are also some that work with C and C++[21][22] - languages that are typically compiled to native code, or work directly on compiled binaries.

A comparison of obfuscation software can be found here

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.[23]

See also

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Notes

  1. ^ Obfuscation: Cloaking your Code from Prying Eyes
  2. ^ Jeff Atwood, May 15 2005
  3. ^ Obfuscation
  4. ^ C++ Tutorials - Obfuscated Code - A Simple Introduction | DreamInCode.net
  5. ^ C Tutorials - Obfuscated Code in C
  6. ^ Pe(a)rls in line noise
  7. ^ http://rochester.pm.org/talks/japh_di scussion.txt
  8. ^ [The International Obfuscated C Code Contest]
  9. ^ "International Obfuscated C Code Winners 1988 - Least likely to compile successfully"
  10. ^ "Reverse Engineering the Twelve Days of Christmas" by Thomas Ball
  11. ^ Don Libes, Obfuscated C and Other Mysteries, John Wiley & Sons, 1993, pp 425. ISBN 0-471-57805-3
  12. ^ Óscar Toledo Gutiérrez: Intel 8080 emulator. 19th IOCCC. Best of Show.
  13. ^ "Can We Obfuscate Programs?" by Boaz Barak
  14. ^ Can I always use the Reflection API if the code is going to be obfuscated?
  15. ^ Seyyedhamzeh, Javad, ABCME: A Novel Metamorphic Engine, 17th National Computer Conference, Sharif University, tehran, Iran, 2012
  16. ^ Open Directory - Computers: Programming: Languages: JavaScript: Tools: Obfuscators
  17. ^ Open Directory - Computers: Programming: Languages: PHP: Development Tools: Obfuscation and Encryption
  18. ^ Open Directory - Computers: Programming: Languages: Java: Development Tools: Obfuscators
  19. ^ Open Directory - Computers: Programming: Component Frameworks: .NET: Tools: Obfuscators
  20. ^ GuardIT for .NET
  21. ^ Cloakware Application Security
  22. ^ Morpher - Compiler Driven Obfuscation
  23. ^ http://lwn.net/Articles/431651/

References

External links

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