X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=libtomcrypt%2Fsrc%2Fpk%2Fasn1%2Fder%2Finteger%2Fder_length_integer.c;fp=libtomcrypt%2Fsrc%2Fpk%2Fasn1%2Fder%2Finteger%2Fder_length_integer.c;h=753ef0e09fde7e8325e8bdc2209e451fab0430d7;hb=66bc25938679f1d6a1d1200f329093d82a5e99b4;hp=0000000000000000000000000000000000000000;hpb=a52ee0733f420ca20224049260d6fc5cf7d8f621;p=zpackage

diff --git a/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c b/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c
new file mode 100644
index 0000000..753ef0e
--- /dev/null
+++ b/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c
@@ -0,0 +1,79 @@
+/* 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.
+ */
+#include "tomcrypt.h"
+
+/**
+  @file der_length_integer.c
+  ASN.1 DER, get length of encoding, Tom St Denis
+*/
+
+
+#ifdef LTC_DER
+/**
+  Gets length of DER encoding of num
+  @param num    The int to get the size of
+  @param outlen [out] The length of the DER encoding for the given integer
+  @return CRYPT_OK if successful
+*/
+int der_length_integer(void *num, unsigned long *outlen)
+{
+   unsigned long z, len;
+   int           leading_zero;
+
+   LTC_ARGCHK(num     != NULL);
+   LTC_ARGCHK(outlen  != NULL);
+
+   if (mp_cmp_d(num, 0) != LTC_MP_LT) {
+      /* positive */
+
+      /* 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) == LTC_MP_YES) {
+         leading_zero = 1;
+      } else {
+         leading_zero = 0;
+      }
+
+      /* size for bignum */
+      z = len = leading_zero + mp_unsigned_bin_size(num);
+   } else {
+      /* it's negative */
+      /* find power of 2 that is a multiple of eight and greater than count bits */
+      z = mp_count_bits(num);
+      z = z + (8 - (z & 7));
+      if (((mp_cnt_lsb(num)+1)==mp_count_bits(num)) && ((mp_count_bits(num)&7)==0)) --z;
+      len = z = z >> 3;
+   }
+
+   /* now we need a length */
+   if (z < 128) {
+      /* short form */
+      ++len;
+   } else {
+      /* long form (relies on z != 0), assumes length bytes < 128 */
+      ++len;
+
+      while (z) {
+         ++len;
+         z >>= 8;
+      }
+   }
+
+   /* we need a 0x02 to indicate it's INTEGER */
+   ++len;
+
+   /* return length */
+   *outlen = len;
+   return CRYPT_OK;
+}
+
+#endif
+
+/* ref:         $Format:%D$ */
+/* git commit:  $Format:%H$ */
+/* commit time: $Format:%ai$ */