captcha.c

const int gifsize;
void captcha(unsigned char im[70*200], unsigned char l[6]);
void makegif(unsigned char im[70*200], unsigned char gif[gifsize]);

#include <unistd.h>
#include <stdint.h>
#include <fcntl.h>
#include <string.h>

static int8_t *lt[];
const int gifsize=17646;

void makegif(unsigned char im[70*200], unsigned char gif[gifsize]) {
 	// tag ; widthxheight ; GCT:0:0:7 ; bgcolor + aspect // GCT
 	// Image Separator // left x top // widthxheight // Flags
	// LZW code size
	memcpy(gif,"GIF89a" "\xc8\0\x46\0" "\x83" "\0\0"
		"\x00\x00\x00"
		"\x10\x10\x10"
		"\x20\x20\x20"
		"\x30\x30\x30"
		"\x40\x40\x40"
		"\x50\x50\x50"
		"\x60\x60\x60"
		"\x70\x70\x70"
		"\x80\x80\x80"
		"\x90\x90\x90"
		"\xa0\xa0\xa0"
		"\xb0\xb0\xb0"
		"\xc0\xc0\xc0"
		"\xd0\xd0\xd0"
		"\xe0\xe0\xe0"
		"\xff\xff\xff"
		"," "\0\0\0\0" "\xc8\0\x46\0" "\0" "\x04",13+48+10+1);

	int x,y;
	unsigned char *i=im;
	unsigned char *p=gif+13+48+10+1;
	for(y=0;y<70;y++) {
		*p++=250; // Data length 5*50=250
		for(x=0;x<50;x++)
		{
			unsigned char a=i[0]>>4,b=i[1]>>4,c=i[2]>>4,d=i[3]>>4;

			p[0]=16|(a<<5);			// bbb10000
			p[1]=(a>>3)|64|(b<<7);	// b10000xb
			p[2]=b>>1;			// 0000xbbb
			p[3]=1|(c<<1);		// 00xbbbb1
			p[4]=4|(d<<3);		// xbbbb100
			i+=4;
			p+=5;
		}
	}

 	// Data length // End of LZW (b10001) // Terminator // GIF End
	memcpy(gif+gifsize-4,"\x01" "\x11" "\x00" ";",4);
}

static const int8_t sw[200]={0, 4, 8, 12, 16, 20, 23, 27, 31, 35, 39, 43, 47, 50, 54, 58, 61, 65, 68, 71, 75, 78, 81, 84, 87, 90, 93, 96, 98, 101, 103, 105, 108, 110, 112, 114, 115, 117, 119, 120, 121, 122, 123, 124, 125, 126, 126, 127, 127, 127, 127, 127, 127, 127, 126, 126, 125, 124, 123, 122, 121, 120, 119, 117, 115, 114, 112, 110, 108, 105, 103, 101, 98, 96, 93, 90, 87, 84, 81, 78, 75, 71, 68, 65, 61, 58, 54, 50, 47, 43, 39, 35, 31, 27, 23, 20, 16, 12, 8, 4, 0, -4, -8, -12, -16, -20, -23, -27, -31, -35, -39, -43, -47, -50, -54, -58, -61, -65, -68, -71, -75, -78, -81, -84, -87, -90, -93, -96, -98, -101, -103, -105, -108, -110, -112, -114, -115, -117, -119, -120, -121, -122, -123, -124, -125, -126, -126, -127, -127, -127, -127, -127, -127, -127, -126, -126, -125, -124, -123, -122, -121, -120, -119, -117, -115, -114, -112, -110, -108, -105, -103, -101, -98, -96, -93, -90, -87, -84, -81, -78, -75, -71, -68, -65, -61, -58, -54, -50, -47, -43, -39, -35, -31, -27, -23, -20, -16, -12, -8, -4};


#define MAX(x,y) ((x>y)?(x):(y))

static int letter(int n, int pos, unsigned char im[70*200], unsigned char swr[200], uint8_t s1, uint8_t s2) {
	int8_t *p=lt[n];
	unsigned char *r=im+200*16+pos;
	unsigned char *i=r;
	int sk1=s1+pos;
	int sk2=s2+pos;
	int mpos=pos;
	int row=0;
	for(;*p!=-101;p++) {
		if(*p<0) {
			if(*p==-100) { r+=200; i=r; sk1=s1+pos; row++; continue; }
			i+=-*p;
			continue;
		}

		if(sk1>=200) sk1=sk1%200;
		int skew=sw[sk1]/16;
		sk1+=(swr[pos+i-r]&0x1)+1;

		if(sk2>=200) sk2=sk2%200;
		int skewh=sw[sk2]/70;
		sk2+=(swr[row]&0x1);

		unsigned char *x=i+skew*200+skewh;
		mpos=MAX(mpos,pos+i-r);
		
		if((x-im)<70*200) *x=(*p)<<4;
		i++;
	}
	return mpos;
}

#define NDOTS 100

uint32_t dr[NDOTS];

static void line(unsigned char im[70*200], unsigned char swr[200], uint8_t s1) {
	int x;
	int sk1=s1;
	for(x=0;x<199;x++) {
		if(sk1>=200) sk1=sk1%200;
		int skew=sw[sk1]/16;
		sk1+=swr[x]&0x3+1;
		unsigned char *i= im+(200*(45+skew)+x);
		i[0]=0; i[1]=0; i[200]=0; i[201]=0;
	}
}

static void dots(unsigned char im[70*200]) {
	int n;
	for(n=0;n<NDOTS;n++) {
		uint32_t v=dr[n];
		unsigned char *i=im+v%(200*67);
		
		i[0]=0xff;
		i[1]=0xff;
		i[2]=0xff;
		i[200]=0xff;
		i[201]=0xff;
		i[202]=0xff;
	}
}
static void blur(unsigned char im[70*200]) {
	unsigned char *i=im;
	int x,y;
	for(y=0;y<68;y++) {
               for(x=0;x<198;x++) {
			unsigned int c11=*i,c12=i[1],c21=i[200],c22=i[201];
			*i++=((c11+c12+c21+c22)/4);
               }
	}
}

static void filter(unsigned char im[70*200]) {
	unsigned char om[70*200];
	unsigned char *i=im;
	unsigned char *o=om;

	memset(om,0xff,sizeof(om));

	int x,y;
	for(y=0;y<70;y++) {
		for(x=4;x<200-4;x++) {
			if(i[0]>0xf0 && i[1]<0xf0) { o[0]=0; o[1]=0; }
			else if(i[0]<0xf0 && i[1]>0xf0) { o[0]=0; o[1]=0; }

			i++;
			o++;
		}
	}

	memmove(im,om,sizeof(om));
}

static const char *letters="abcdafahijklmnopqrstuvwxyz";

void captcha(unsigned char im[70*200], unsigned char l[6]) {
	unsigned char swr[200];
	uint8_t s1,s2;

	int f=open("/dev/urandom",O_RDONLY);
	read(f,l,5); read(f,swr,200); read(f,dr,sizeof(dr)); read(f,&s1,1); read(f,&s2,1);
	close(f);

	memset(im,0xff,200*70); s1=s1&0x7f; s2=s2&0x3f; l[0]%=25; l[1]%=25; l[2]%=25; l[3]%=25; l[4]%=25; l[5]=0;
	int p=30; p=letter(l[0],p,im,swr,s1,s2); p=letter(l[1],p,im,swr,s1,s2); p=letter(l[2],p,im,swr,s1,s2); p=letter(l[3],p,im,swr,s1,s2); letter(l[4],p,im,swr,s1,s2);
	dots(im); blur(im); filter(im); line(im,swr,s1); 
	l[0]=letters[l[0]]; l[1]=letters[l[1]]; l[2]=letters[l[2]]; l[3]=letters[l[3]]; l[4]=letters[l[4]];
}

#ifdef CAPTCHA

int main() {
	char l[6];
	unsigned char im[70*200];
	unsigned char gif[gifsize];

	captcha(im,l);
	makegif(im,gif);

	write(1,gif,gifsize);
	write(2,l,5);

	return 0;
}

#endif

#include "f.h"