--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c	Wed Mar 08 13:23:58 2006 +0000
@@ -0,0 +1,110 @@
+/* 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
+
+/**
+  Read a mp_int integer
+  @param in       The DER encoded data
+  @param inlen    Size of DER encoded data
+  @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 x, y, z;
+   int           err;
+
+   LTC_ARGCHK(num    != NULL);
+   LTC_ARGCHK(in     != NULL);
+
+   /* min DER INTEGER is 0x02 01 00 == 0 */
+   if (inlen < (1 + 1 + 1)) {
+      return CRYPT_INVALID_PACKET;
+   }
+
+   /* ok expect 0x02 when we AND with 0001 1111 [1F] */
+   x = 0;
+   if ((in[x++] & 0x1F) != 0x02) {
+      return CRYPT_INVALID_PACKET;
+   }
+
+   /* now decode the len stuff */
+   z = in[x++];
+
+   if ((z & 0x80) == 0x00) {
+      /* short form */
+
+      /* will it overflow? */
+      if (x + z > inlen) {
+         return CRYPT_INVALID_PACKET;
+      }
+     
+      /* no so read it */
+      if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, z))) != CRYPT_OK) {
+         return err;
+      }
+   } else {
+      /* long form */
+      z &= 0x7F;
+      
+      /* will number of length bytes overflow? (or > 4) */
+      if (((x + z) > inlen) || (z > 4) || (z == 0)) {
+         return CRYPT_INVALID_PACKET;
+      }
+
+      /* now read it in */
+      y = 0;
+      while (z--) {
+         y = ((unsigned long)(in[x++])) | (y << 8);
+      }
+
+      /* now will reading y bytes overrun? */
+      if ((x + y) > inlen) {
+         return CRYPT_INVALID_PACKET;
+      }
+
+      /* no so read it */
+      if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, y))) != CRYPT_OK) {
+         return err;
+      }
+   }
+
+   /* see if it's negative */
+   if (in[x] & 0x80) {
+      mp_int tmp;
+      if (mp_init(&tmp) != MP_OKAY) {
+         return CRYPT_MEM;
+      }
+
+      if (mp_2expt(&tmp, mp_count_bits(num)) != MP_OKAY || mp_sub(num, &tmp, num) != MP_OKAY) {
+         mp_clear(&tmp);
+         return CRYPT_MEM;
+      }
+      mp_clear(&tmp);
+   } 
+
+   return CRYPT_OK;
+
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c,v $ */
+/* $Revision: 1.2 $ */
+/* $Date: 2005/06/01 00:06:05 $ */