--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/pk/asn1/der/der_decode_integer.c	Fri May 06 13:23:02 2005 +0000
@@ -0,0 +1,98 @@
+/* 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_decode_integer.c
+  ASN.1 DER, decode an integer, Tom St Denis
+*/
+
+
+#ifdef LTC_DER
+
+/* decodes a DER INTEGER in [in].  You have to tell this function
+ * how many bytes are available [inlen].  It will then attempt to 
+ * read the INTEGER.  If all goes well it stores the number of bytes
+ * read in [inlen] and the number in [num].
+ */
+/**
+  Read a mp_int integer
+  @param in       The DER encoded data
+  @param inlen    [in] Size of the in data, [out] number of bytes read
+  @param num      The first mp_int to decode
+  @return CRYPT_OK if successful
+*/
+int der_decode_integer(const unsigned char *in, unsigned long *inlen, mp_int *num)
+{
+   unsigned long tmplen, y, z;
+
+   LTC_ARGCHK(num    != NULL);
+   LTC_ARGCHK(in     != NULL);
+   LTC_ARGCHK(inlen  != NULL);
+
+   /* save copy of max output size */
+   tmplen = *inlen;
+   *inlen = 0;
+
+   /* min DER INTEGER is 0x02 01 00 == 0 */
+   if (tmplen < (1 + 1 + 1)) {
+      return CRYPT_INVALID_PACKET;
+   }
+
+   /* ok expect 0x02 when we AND with 0011 1111 [3F] */
+   if ((*in++ & 0x3F) != 0x02) {
+      return CRYPT_INVALID_PACKET;
+   }
+   ++(*inlen);
+
+   /* now decode the len stuff */
+   z = *in++;
+   ++(*inlen);
+
+   if ((z & 0x80) == 0x00) {
+      /* short form */
+
+      /* will it overflow? */
+      if (*inlen + z > tmplen) {
+         return CRYPT_INVALID_PACKET;
+      }
+     
+      /* no so read it */
+      (*inlen) += z;
+      return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, z));
+   } else {
+      /* long form */
+      z &= 0x7F;
+      
+      /* will number of length bytes overflow? (or > 4) */
+      if (((*inlen + z) > tmplen) || (z > 4)) {
+         return CRYPT_INVALID_PACKET;
+      }
+
+      /* now read it in */
+      y = 0;
+      while (z--) {
+         y = ((unsigned long)(*in++)) | (y << 8);
+         ++(*inlen);
+      }
+
+      /* now will reading y bytes overrun? */
+      if ((*inlen + y) > tmplen) {
+         return CRYPT_INVALID_PACKET;
+      }
+
+      /* no so read it */
+      (*inlen) += y;
+      return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, y));
+   }
+}
+
+#endif