git.distorted.org.uk Git - u/mdw/catacomb/blob - utils/ecptdecompress.c

   1 #include <stdio.h>
   2 #include <string.h>
   3 #include <stdlib.h>
   4
   5 #include <mLib/alloc.h>
   6 #include <mLib/hex.h>
   7 #include <mLib/dstr.h>
   8
   9 #include "ec.h"
  10 #include "mp.h"
  11 #include "rand.h"
  12
  13 static void puthex(const char *name, mp *x, size_t n)
  14 {
  15   dstr d = DSTR_INIT;
  16   hex_ctx hc;
  17   char *p;
  18
  19   if (!n) n = mp_octets(x);
  20   p = xmalloc(n);
  21   hex_init(&hc);
  22   hc.indent = "";
  23   hc.maxline = 0;
  24   mp_storeb(x, p, n);
  25   hex_encode(&hc, p, n, &d);
  26   hex_encode(&hc, 0, 0, &d);
  27   printf("  %s 0x", name);
  28   dstr_write(&d, stdout);
  29   putchar('\n');
  30   dstr_destroy(&d);
  31   xfree(p);
  32 }
  33
  34 int main(int argc, char *argv[])
  35 {
  36   ec_curve *c;
  37   ec_info ei;
  38   ec pt = EC_INIT;
  39   qd_parse qd;
  40   hex_ctx hc;
  41   dstr d = DSTR_INIT;
  42   size_t n;
  43   octet *p;
  44   mp *x, *y = 0, *yy = 0;
  45   const char *err;
  46
  47   qd.p = argv[1];
  48   qd.e = 0;
  49   if ((c = ec_curveparse(&qd)) == 0 || !qd_eofp(&qd)) {
  50     fprintf(stderr, "bad curve: %s\n", qd.e);
  51     exit(1);
  52   }
  53   n = c->f->noctets;
  54
  55   ei.c = c;
  56   ei.r = mp_readstring(MP_NEW, argv[2], 0, 0);
  57   ei.h = mp_readstring(MP_NEW, argv[3], 0, 0);
  58
  59   EC_CREATE(&ei.g);
  60   hex_init(&hc);
  61   hex_decode(&hc, argv[4], strlen(argv[4]), &d);
  62   hex_decode(&hc, 0, 0, &d);
  63   p = (octet *)d.buf;
  64   if (p[0] == 0) {
  65     EC_SETINF(&ei.g);
  66   } else {
  67     if (d.len < n + 1) {
  68       fprintf(stderr, "missing x\n");
  69       exit(1);
  70     }
  71     x = mp_loadb(MP_NEW, p + 1, n);
  72     if (p[0] & 0x04) {
  73       if (d.len < 2 * n + 1) {
  74         fprintf(stderr, "missing y\n");
  75         exit(1);
  76       }
  77       y = mp_loadb(MP_NEW, p + n + 1, n);
  78     }
  79     if (p[0] & 0x02) {
  80       if (!EC_FIND(c, &pt, x)) {
  81         fprintf(stderr, "no matching y\n");
  82         exit(1);
  83       }
  84       yy = MP_COPY(pt.y);
  85       ec_destroy(&pt);
  86       switch (F_TYPE(c->f)) {
  87         case FTY_PRIME:
  88           if (!MP_ISODD(yy) != !(p[0] & 1))
  89             yy = mp_sub(yy, c->f->m, yy);
  90           break;
  91         case FTY_BINARY:
  92           if (MP_ISZERO(x))
  93             yy = F_SQRT(c->f, MP_NEW, c->b);
  94           else {
  95             mp *xx = F_SQR(c->f, MP_NEW, x);
  96             mp *b = F_MUL(c->f, MP_NEW, xx, c->a);
  97             mp *xxx = F_MUL(c->f, MP_NEW, xx, x);
  98             b = F_ADD(c->f, b, b, xxx);
  99             b = F_ADD(c->f, b, b, c->b);
 100             xx = F_INV(c->f, xx, xx);
 101             b = F_MUL(c->f, b, b, xx);
 102             mp_drop(xxx);
 103             mp_drop(xx);
 104             yy = F_QUADSOLVE(c->f, MP_NEW, b);
 105             if (!MP_ISODD(yy) != !(p[0] & 1))
 106               yy = mp_add(yy, yy, MP_ONE);
 107             yy = F_MUL(c->f, yy, yy, x);
 108           }
 109           break;
 110         default:
 111           abort();
 112       }
 113     }
 114     if (y && yy && !MP_EQ(y, yy)) {
 115       fprintf(stderr, "inconsistent answers\n");
 116       exit(1);
 117     }
 118     ei.g.x = x;
 119     ei.g.y = mp_copy(y ? y : yy);
 120     mp_drop(y); mp_drop(yy);
 121   }
 122
 123   if ((err = ec_checkinfo(&ei, &rand_global)) != 0) {
 124     fprintf(stderr, "bad curve: %s\n", err);
 125     exit(0);
 126   }
 127   puthex("p", ei.c->f->m, 0);
 128   puthex("a", ei.c->a, c->f->noctets);
 129   puthex("b", ei.c->b, c->f->noctets);
 130   puthex("r", ei.r, c->f->noctets);
 131   printf("  h "); mp_writefile(ei.h, stdout, 10); putchar('\n');
 132   puthex("gx", ei.g.x, c->f->noctets);
 133   puthex("gy", ei.g.y, c->f->noctets);
 134   ec_freeinfo(&ei);
 135   dstr_destroy(&d);
 136   return (0);
 137 }