--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/der_encode_integer.c	Sun Dec 19 11:34:45 2004 +0000
@@ -0,0 +1,93 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+
+#include "mycrypt.h"
+
+/* Exports a positive bignum as DER format (upto 2^32 bytes in size) */
+int der_encode_integer(mp_int *num, unsigned char *out, unsigned long *outlen)
+{  
+   unsigned long tmplen, x, y, z;
+   int           err, leading_zero;
+
+   _ARGCHK(num    != NULL);
+   _ARGCHK(out    != NULL);
+   _ARGCHK(outlen != NULL);
+
+   /* find out how big this will be */
+   if ((err = der_length_integer(num, &tmplen)) != CRYPT_OK) {
+      return err;
+   }
+
+   if (*outlen < tmplen) {
+      return CRYPT_BUFFER_OVERFLOW;
+   }
+
+   /* we only need a leading zero if the msb of the first byte is one */
+   if ((mp_count_bits(num) & 7) == 7 || mp_iszero(num) == MP_YES) {
+      leading_zero = 1;
+   } else {
+      leading_zero = 0;
+   }
+
+   /* get length of num in bytes (plus 1 since we force the msbyte to zero) */
+   y = mp_unsigned_bin_size(num) + leading_zero;
+
+   /* now store initial data */
+   *out++ = 0x02;
+   if (y < 128) {
+      /* short form */
+      *out++ = (unsigned char)y;
+   } else {
+      /* long form (relies on y != 0) */
+
+      /* get length of length... ;-) */
+      x = y;
+      z = 0;
+      while (x) {
+         ++z;
+         x >>= 8;
+      }
+      
+      /* store length of length */
+      *out++ = 0x80 | ((unsigned char)z);
+
+      /* now store length */
+      
+      /* first shift length up so msbyte != 0 */
+      x = y;
+      while ((x & 0xFF000000) == 0) {
+          x <<= 8;
+      }
+
+      /* now store length */
+      while (z--) {
+         *out++ = (unsigned char)((x >> 24) & 0xFF);
+         x <<= 8;
+      }
+   }
+
+   /* now store msbyte of zero if num is non-zero */
+   if (leading_zero) {
+      *out++ = 0x00;
+   }
+
+   /* if it's not zero store it as big endian */
+   if (mp_iszero(num) == MP_NO) {
+      /* now store the mpint */
+      if ((err = mp_to_unsigned_bin(num, out)) != MP_OKAY) {
+          return mpi_to_ltc_error(err);
+      }
+   }
+
+   /* we good */
+   *outlen = tmplen; 
+   return CRYPT_OK;
+}