The 27th International Obfuscated C Code Contest

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The results of the 27th International Obfuscated C Code Contest were announced earlier this month. The code is amazing. It runs. It’s horrifyingly cryptic.

Obfuscated C is exactly the kind of coding I try to avoid. The goal is to deliberately make the code difficult to read. The obfuscation can also present itself as visually symmetrical or formatted to create an image.

While I admire the degrees to which you can make C look complex or pretty, my goal is to teach. The code examples I use must be presented in a way that’s easy to understand. Still, obfuscating C is possible and enjoyed by dozens of programmers, hence the contest.

Different categories of obfuscated C are possible. For example, the one-line cryptic like this:

int main(int b,char**i){long long n=B,a=I^n,r=(a/b&a)>>4,y=atoi(*++i),_=(((a^n/b)*(y>>T)|y>>S)&r)|(a^r);printf("%.8s\n",(char*)&_);}

I’m also fond of users who freely format their code like this:

                                                      #\
                                define C(c           /**/)#c
                               /*size=3173*/#include<stdio.h>
                            /*crc=b7f9ecff.*/#include<stdlib.h>
                           /*Mile/Adele_von_Ascham*/#include<time.h>
                           typedef/**/int(I);I/*:3*/d,i,j,a,b,l,u[16],v
                           [18],w[36],x,y,z,k;char*P="\n\40(),",*p,*q,*t[18],m[4];
                          void/**/O(char*q){for(;*q;q++)*q>32?z=111-*q?z=(z+*q)%185,(k?
                          k--:(y=z%37,(x=z/37%7)?printf(*t,t[x],y?w[y-1]:95):y>14&&y<33?x
                          =y>15,printf(t[15+x],x?2<<y%16:l,x?(1<<y%16)-1:1):puts(t[y%28])))
                          ,0:z+82:0;}void/**/Q(I(p),I*q){for(x=0;x<p;x++){q[x]=x;}for(;--p
    >1;q[p]=y)y          =q[x=rand()%-~p],q[x]=q[p];}char/**/n[999]=C(Average?!nQVQd%R>Rd%
  R%          %RNIPRfi#VQ}R;TtuodtsRUd%RUd%RUOSetirwf!RnruterR{RTSniamRtniQ>h.oidts<edulc
 ni                   #V>rebmun<=NIPD-RhtiwRelipmocResaelPRrorre#QNIPRfednfi#V__ELIF__R_
Re               nifed#V~-VU0V;}V{R= R][ORrahcRdengisnuRtsnocRcitatsVesle#Vfidne#V53556
 .           .1RfoRegnarRehtRniRre   getniRnaRsiR]NIP[R erehwQQc.tuptuoR>Rtxt.tupniR
 <         R]NIP[R:egasuV_Redulcn i#VfednfiVfednuVenife dVfedfiVQc%Rs%#V);I/**/main(
  I(      f),char**e){if(f){for(i=    time(NULL),p=n,q=  n+998,x=18;x;p++){*p>32&&!(
         *--q=*p>80&&*p<87?P[*p-   81]:*     p)?t  [( --  x)]=q+1:q;}if(f-2||(d=atoi
        (e[1]))<1||65536<d){;O("   \"");             goto  O;}srand(i);Q(16,u);i=0;Q(
       36,w);for(;i<36; i++){w[i]   +=w           [i]<26 ? 97:39; }O(C(ouoo9oBotoo%]#
      ox^#oy_#ozoou#o{ a#o|b#o}c#                o~d#oo-e   #oo.  f#oo/g#oo0h#oo1i#oo
     2j#oo3k#oo4l#o   p));for(j                   =8;EOF   -(i=   getchar());l+=1){a=1+
    rand()%16;for(b  =0;b<a||i-                           main   (0,e);b++)x=d^d/4^d/8^d/
    32,d=  (d/  2|x<<15)&65535;                          b|=   !l<<17;Q(18,v);for(a=0;a<18;
    a++     ){if( (b&(1<<(i=v[a]      ))))*                 m=75+i,O(m),j=i<17&&j<i?i:j;}O(C(
    !)           ); }O(C(oqovoo97o    /n!));i=           0;for(;i<8;O(m))m[2]=35,*m=56+u[i],m[1
    ]=          75   +i++;O(C(oA!oro   oqoo9)          );k=112-j*7;O(C(6o.!Z!Z#5o-!Y!Y#4~!X!X#3}
     !W  !W     #2    |!V!V#1{!U!U#0z!            T!T#/y!S!S#.x!R!R#-w!Q!Q#ooAv!P!P#+o#!O!O#*t!N!
       N#      oo       >s!M!M#oo=r!L!L#oo<q!K!K#   &pIo@:;= oUm#oo98m##oo9=8m#oo9oUm###oo9;=8m#o
               o9   oUm##oo9=oUm#oo98m####          o09]    #o1:^#o2;_#o3<o  ou#o4=a#o5>b#o6?c#o
             7@d#o8A e#o    9B    f#o:Cg#o;          D     h#o<Ei #o=Fj#o>   Gk#o?Hl#oo9os#####
           ));d=0                                          ;}          O:    for(x=y=0;x<8;++
          x)y|=                                                               d&(1<<u[x])?
          1<<                                                               x:0;return
           /*                                                               :9    */
            y                                                                ;    }

Building these programs requires a few command line options to get things working, which I think of as cheating. For example, you can avoid using #include preprocessor directives in your code if you use the ‑include command line switch. Still, all this nonsense is for thrills.

I’ve tried to write obfuscated C, but haven’t written anything that delights to me to the degree of the cryptic or pretty code I’ve seen. From my desire to teach, I have an aversion to making things difficult to figure out. Therefore, I both appreciate obfuscated C but recognize that I’m unable to do it myself.

As I feel compelled, here’s my lame version of obfuscated C, though it’s pretty obvious what I’m doing:

2021_01_23-Lesson.c

int main() {puts("Hello, World!");return 0;}

All I did above is put the entire main() function on a single line. This is the entire code, by the way. To compile, you use the following command at the prompt:

clang -include stdio.h 0123.c

Again, I think specifying the -include switch is cheating, but it keeps the source code compact. My attempt at obfuscation merely takes advantage of C’s capability to ignore whitespace. Likewise, you can pad the whitespace, which is done in the second example shown earlier.

If it’s your goal to obfuscate your C code, great! Have fun. Enter the contest (use the link above). But please don’t deliberately or otherwise obfuscate your code. C can be cryptic, but it’s an appreciated art form to make it readable.

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