X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/c61ee18cea55601bfe24e88dbb3a4ddf43fd6844..b2776fdf2a98ea586bbdad50eca4ed95e967b0d7:/keysz.h

diff --git a/keysz.h b/keysz.h
index 5a49740..97ed144 100644
--- a/keysz.h
+++ b/keysz.h
@@ -85,6 +85,63 @@ extern size_t keysz(size_t /*sz*/, const octet */*ksz*/);
 #define KSZ_ASSERT(pre, sz)						\
   assert(((void)"Bad key size for " #pre, KSZ_CHECK(pre, sz)))
 
+/*----- Key size conversions ----------------------------------------------*/
+
+/* --- @keysz_fromdl@, @_fromschnorr@, @_fromif@, @_fromec@ --- *
+ *
+ * Arguments:	@double nbits@ = key size
+ *
+ * Returns:	Equivalent symmetric key size.
+ *
+ * Use:		Converts key lengths of various kinds of reference problems
+ *		to (roughly) equivalent symmetric key sizes.
+ *
+ *		  * Given the bit length of %$p$%, @keysz_fromdl@ returns a
+ *		    key size representing the difficulty of computing
+ *		    discrete logarithms in %$\gf{p}$%, for %$p$% prime or a
+ *		    small power of a prime.
+ *
+ *		  * Given the bit length of %$r$%, @keysz_fromschnorr@
+ *		    returns a key size representing the difficulty of
+ *		    computing discrete logarithms in a subgroup of %$\gf{q}$%
+ *		    of order %$r$%.
+ *
+ *		  * Given the bit length of %$n$%, @keysz_fromif@ returns a
+ *		    key size representing the difficulty of factoring a
+ *		    `hard' number %$n = p q$%, where %$p$% and %$q$% are
+ *		    primes of (near enough) the same length.
+ *
+ *		  * Given the bit length of %$r$%, @keysz_fromec@ returns a
+ *		    key size representing the difficulty of computing
+ *		    discrete logarithms in a subgroup of order-%$r$% of an
+ *		    elliptic curve over a finite field.
+ *
+ *		These functions take and return @double@ rather than an
+ *		integer type in order to preserve precision between
+ *		conversions.
+ */
+
+extern double keysz_fromdl(double /*nbits*/);
+extern double keysz_fromschnorr(double /*nbits*/);
+extern double keysz_fromif(double /*nbits*/);
+extern double keysz_fromec(double /*nbits*/);
+
+/* --- @keysz_todl@, @_toschnorr@, @_toif@, @_toec@ --- *
+ *
+ * Arguments:	@unsigned long nbits@ = symmetric key size
+ *
+ * Returns:	Equivalent key size.
+ *
+ * Use:		Converts symmetric key sizes to (roughly) equivalent key
+ *		sizes for various kinds of reference problems.  These are the
+ *		approximate inverses of the functions above.
+ */
+
+extern double keysz_todl(double /*nbits*/);
+extern double keysz_toschnorr(double /*nbits*/);
+extern double keysz_toif(double /*nbits*/);
+extern double keysz_toec(double /*nbits*/);
+
 /*----- That's all, folks -------------------------------------------------*/
 
 #ifdef __cplusplus