--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/asn1/der/integer/der_encode_integer.c	Wed Mar 08 13:23:58 2006 +0000
@@ -0,0 +1,128 @@
+/* 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 "tomcrypt.h"
+
+/**
+  @file der_encode_integer.c
+  ASN.1 DER, encode an integer, Tom St Denis
+*/
+
+
+#ifdef LTC_DER
+
+/* Exports a positive bignum as DER format (upto 2^32 bytes in size) */
+/**
+  Store a mp_int integer
+  @param num      The first mp_int to encode
+  @param out      [out] The destination for the DER encoded integers
+  @param outlen   [in/out] The max size and resulting size of the DER encoded integers
+  @return CRYPT_OK if successful
+*/
+int der_encode_integer(mp_int *num, unsigned char *out, unsigned long *outlen)
+{  
+   unsigned long tmplen, y;
+   int           err, leading_zero;
+
+   LTC_ARGCHK(num    != NULL);
+   LTC_ARGCHK(out    != NULL);
+   LTC_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;
+   }
+
+   if (mp_cmp_d(num, 0) != MP_LT) {
+      /* we only need a leading zero if the msb of the first byte is one */
+      if ((mp_count_bits(num) & 7) == 0 || 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;
+   } else {
+      leading_zero = 0;
+      y            = mp_count_bits(num);
+      y            = y + (8 - (y & 7));
+      y            = y >> 3;
+
+   }
+
+   /* now store initial data */
+   *out++ = 0x02;
+   if (y < 128) {
+      /* short form */
+      *out++ = (unsigned char)y;
+   } else if (y < 256) {
+      *out++ = 0x81;
+      *out++ = y;
+   } else if (y < 65536UL) {
+      *out++ = 0x82;
+      *out++ = (y>>8)&255;
+      *out++ = y;
+   } else if (y < 16777216UL) {
+      *out++ = 0x83;
+      *out++ = (y>>16)&255;
+      *out++ = (y>>8)&255;
+      *out++ = y;
+   } else {
+      return CRYPT_INVALID_ARG;
+   }
+
+   /* 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_cmp_d(num, 0) == MP_GT) {
+      /* now store the mpint */
+      if ((err = mp_to_unsigned_bin(num, out)) != MP_OKAY) {
+          return mpi_to_ltc_error(err);
+      }
+   } else if (mp_iszero(num) != MP_YES) {
+      mp_int tmp;
+      /* negative */
+      if (mp_init(&tmp) != MP_OKAY) {
+         return CRYPT_MEM;
+      }
+
+      /* 2^roundup and subtract */
+      y = mp_count_bits(num);
+      y = y + (8 - (y & 7));
+      if (mp_2expt(&tmp, y) != MP_OKAY || mp_add(&tmp, num, &tmp) != MP_OKAY) {
+         mp_clear(&tmp);
+         return CRYPT_MEM;
+      }
+
+      if ((err = mp_to_unsigned_bin(&tmp, out)) != MP_OKAY) {
+         mp_clear(&tmp);
+         return mpi_to_ltc_error(err);
+      }
+      mp_clear(&tmp);
+   }
+
+   /* we good */
+   *outlen = tmplen; 
+   return CRYPT_OK;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_encode_integer.c,v $ */
+/* $Revision: 1.1 $ */
+/* $Date: 2005/05/16 15:08:11 $ */