Move from xxtea to arc4

arc4 has known attacks, but you need a lot of data first.  More data
that we'll have tokens.

src/Makefile

@@ -5,7 +5,7 @@ all: build
 
 build: $(TARGETS)
 
-in.tokend: in.tokend.o xxtea.o common.o
+in.tokend: in.tokend.o arc4.o common.o
 pointscli: pointscli.o common.o
 
 puzzles.cgi: puzzles.cgi.o common.o

src/arc4.c

@@ -0,0 +1,54 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include "arc4.h"
+
+#define swap(a, b) do {int _swap=a; a=b, b=_swap;} while (0)
+
+void
+arc4_init(struct arc4_ctx *ctx, uint8_t const *key, size_t keylen)
+{
+  int i;
+  int j = 0;
+
+  for (i = 0; i < 256; i += 1) {
+    ctx->S[i] = i;
+  }
+
+  for (i = 0; i < 256; i += 1) {
+    j = (j + ctx->S[i] + key[i % keylen]) % 256;
+    swap(ctx->S[i], ctx->S[j]);
+  }
+  ctx->i = 0;
+  ctx->j = 0;
+}
+
+void
+arc4_crypt(struct arc4_ctx *ctx,
+           uint8_t *obuf, uint8_t const *ibuf, size_t buflen)
+{
+  int    i = ctx->i;
+  int    j = ctx->j;
+  size_t k;
+
+  for (k = 0; k < buflen; k += 1) {
+    uint8_t mask;
+
+    i = (i + 1) % 256;
+    j = (j + ctx->S[i]) % 256;
+    swap(ctx->S[i], ctx->S[j]);
+    mask = ctx->S[(ctx->S[i] + ctx->S[j]) % 256];
+    obuf[k] = ibuf[k] ^ mask;
+  }
+  ctx->i = i;
+  ctx->j = j;
+}
+
+void
+arc4_crypt_buffer(uint8_t const *key, size_t keylen,
+                  uint8_t *buf, size_t buflen)
+{
+  struct arc4_ctx ctx;
+
+  arc4_init(&ctx, key, keylen);
+  arc4_crypt(&ctx, buf, buf, buflen);
+}

src/arc4.h

@@ -0,0 +1,19 @@
+#ifndef __ARC4_H__
+#define __ARC4_H__
+
+#include <stdint.h>
+#include <stdlib.h>
+
+struct arc4_ctx {
+  uint8_t S[256];
+  uint8_t i;
+  uint8_t j;
+};
+
+void arc4_init(struct arc4_ctx *ctx, uint8_t const *key, size_t keylen);
+void arc4_crypt(struct arc4_ctx *ctx,
+                uint8_t *obuf, uint8_t const *ibuf, size_t buflen);
+void arc4_crypt_buffer(uint8_t const *key, size_t keylen,
+                       uint8_t *buf, size_t buflen);
+
+#endif

src/claim.cgi.c

@@ -64,7 +64,7 @@ main(int argc, char *argv[])
     category[i] = '\0';
 
     {
-      char line[TEAM_MAX + TOKEN_MAX + 1];
+      char line[200];
 
       my_snprintf(line, sizeof(line),
                   "%s %s", team, token);

src/in.tokend.c

@@ -10,7 +10,7 @@
 #include <string.h>
 #include <ctype.h>
 #include "common.h"
-#include "xxtea.h"
+#include "arc4.h"
 
 #define itokenlen 3
 
@@ -73,7 +73,8 @@ main(int argc, char *argv[])
   size_t  servicelen;
   char    token[80];
   size_t  tokenlen;
-  uint32_t key[4];
+  uint8_t key[256];
+  size_t  keylen;
 
   /* Seed the random number generator.  This ought to be unpredictable
      enough for a contest. */
@@ -83,7 +84,7 @@ main(int argc, char *argv[])
   {
     ssize_t len;
 
-    len = read(0, service, sizeof(service) - 1);
+    len = read(0, service, sizeof(service));
     for (servicelen = 0;
          (servicelen < len) && isalnum(service[servicelen]);
          servicelen += 1);
@@ -92,21 +93,22 @@ main(int argc, char *argv[])
   /* Read in that service's key. */
   {
     int fd;
-    size_t  len;
+    int ret;
 
-    fd = open(srv_path("token.keys/%s", service), O_RDONLY);
+    fd = open(srv_path("token.keys/%*s", servicelen, service), O_RDONLY);
     if (-1 == fd) {
       write(1, "!nosvc", 6);
       return 0;
     }
 
-    len = read(fd, &key, 16);
-    close(fd);
-
-    if (16 != len) {
-      write(1, "!shortkey", 9);
+    ret = read(fd, &key, sizeof(key));
+    if (-1 == ret) {
+      write(1, "!read", 5);
       return 0;
     }
+    keylen = (size_t)ret;
+
+    close(fd);
   }
 
   /* Create the token. */
@@ -158,19 +160,14 @@ main(int argc, char *argv[])
     }
   }
 
-  /* Encrypt the token.  Note that now tokenlen is in uint32_ts, not
-     chars!  Also remember that token must be big enough to hold a
-     multiple of 4 chars, since tea will go ahead and jumble them up for
-     you.  If the compiler aligns words this shouldn't be a problem. */
+  /* Encrypt the token. */
   {
-    tokenlen = (tokenlen + (tokenlen % sizeof(uint32_t))) / sizeof(uint32_t);
-
-    tea_encode(key, (uint32_t *)token, tokenlen);
+    arc4_crypt_buffer(key, keylen, (uint8_t *)token, tokenlen);
   }
 
   /* Send it back.  If there's an error here, it's okay.  Better to have
      unclaimed tokens than unclaimable ones. */
-  write(1, token, tokenlen * sizeof(uint32_t));
+  write(1, token, tokenlen);
 
   return 0;
 }

src/puzzler.cgi.c

@@ -68,7 +68,7 @@ main(int argc, char *argv[])
   }
 
   {
-    char line[TEAM_MAX + CAT_MAX + sizeof(points_str) + 2];
+    char line[200];
 
     my_snprintf(line, sizeof(line),
                "%s %s %ld", team, category, points);

src/puzzles.cgi.c

@@ -19,11 +19,12 @@ longcmp(long *a, long *b)
 #define PUZZLES_MAX 100
 
 /** Keeps track of the most points yet awarded in each category */
+int    ncats = 0;
 struct {
   char cat[CAT_MAX];
   long points;
 } points_by_cat[PUZZLES_MAX];
-int ncats = 0;
+
 
 size_t
 read_until_char(FILE *f, char *buf, size_t buflen, char delim)
@@ -70,8 +71,6 @@ main(int argc, char *argv[])
       read_until_char(f, points_str, sizeof(points_str), '\n');
       points = atol(points_str);
 
-      printf("%s %ld\n", cat, points);
-
       for (i = 0; i < ncats; i += 1) {
         if (0 == strcmp(cat, points_by_cat[i].cat)) break;
       }

src/xxtea.c

@@ -1,51 +0,0 @@
-#include <stdint.h>
-#include <stddef.h>
-
-#define DELTA 0x9e3779b9
-#define MX ((z>>5^y<<2) + (y>>3^z<<4)) ^ ((sum^y) + (k[(p&3)^e] ^ z));
-
-void
-btea(uint32_t *v, int n, uint32_t const k[4])
-{
-  uint32_t y, z, sum;
-  unsigned p, rounds, e;
-
-  if (n > 1) {          /* Coding Part */
-    rounds = 6 + 52/n;
-    sum = 0;
-    z = v[n-1];
-    do {
-      sum += DELTA;
-      e = (sum >> 2) & 3;
-      for (p=0; p<n-1; p++)
-        y = v[p+1], z = v[p] += MX;
-      y = v[0];
-      z = v[n-1] += MX;
-    } while (--rounds);
-  } else if (n < -1) {  /* Decoding Part */
-    n = -n;
-    rounds = 6 + 52/n;
-    sum = rounds*DELTA;
-    y = v[0];
-    do {
-      e = (sum >> 2) & 3;
-      for (p=n-1; p>0; p--)
-        z = v[p-1], y = v[p] -= MX;
-      z = v[n-1];
-      y = v[0] -= MX;
-    } while ((sum -= DELTA) != 0);
-  }
-}
-
-void
-tea_encode(uint32_t const key[4], uint32_t *buf, size_t buflen)
-{
-  btea(buf, buflen, key);
-}
-
-void
-tea_decode(uint32_t const key[4], uint32_t *buf, size_t buflen)
-{
-  btea(buf, -buflen, key);
-}
-

src/xxtea.h

@@ -1,2 +0,0 @@
-void tea_encode(uint32_t const key[4], uint32_t *buf, size_t buflen);
-void tea_decode(uint32_t const key[4], uint32_t *buf, size_t buflen);