From: mdw <mdw>
Date: Sat, 17 Jun 2000 10:56:00 +0000 (+0000)
Subject: New key size interface.
X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/commitdiff_plain/b7e9df9cae301938fde97061ef73a3ea37a6ad40

New key size interface.
---

diff --git a/gcipher.h b/gcipher.h
index 4831913..b8c34bf 100644
--- a/gcipher.h
+++ b/gcipher.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: gcipher.h,v 1.1 1999/12/10 23:16:01 mdw Exp $
+ * $Id: gcipher.h,v 1.2 2000/06/17 10:56:00 mdw Exp $
  *
  * Generic symmetric cipher interface
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: gcipher.h,v $
+ * Revision 1.2  2000/06/17 10:56:00  mdw
+ * New key size interface.
+ *
  * Revision 1.1  1999/12/10 23:16:01  mdw
  * Generic interface.
  *
@@ -46,20 +49,16 @@
 
 #include <stddef.h>
 
-/*----- Generic symmetric cipher interface --------------------------------*/
+#include <mLib/bits.h>
 
-typedef struct gccipher_base {
-  const char *name;			/* Cipher name */
-  size_t keysz;				/* Preferred key size in bytes */
-  size_t blksz;				/* Block size or zero if none */
-} gccipher_base;
+/*----- Generic symmetric cipher interface --------------------------------*/
 
 typedef struct gcipher {
   const struct gcipher_ops *ops;	/* Pointer to cipher operations */
 } gcipher;
 
 typedef struct gcipher_ops {
-  const struct gccipher_base *b;	/* Pointer to basic information */
+  const struct gccipher *c;		/* Pointer to cipher class */
   void (*encrypt)(gcipher */*c*/, const void */*s*/,
 		  void */*t*/, size_t /*sz*/);
   void (*decrypt)(gcipher */*c*/, const void */*s*/,
@@ -70,10 +69,57 @@ typedef struct gcipher_ops {
 } gcipher_ops;
 
 typedef struct gccipher {
-  gccipher_base b;
+  const char *name;			/* Cipher name */
+  const octet *keysz;			/* Preferred key size table */
+  size_t blksz;				/* Block size or zero if none */
   gcipher *(*init)(const void */*k*/, size_t /*sz*/);
 } gccipher;
 
+/*----- Key size management -----------------------------------------------*/
+
+/* --- Key size type constants --- *
+ *
+ * A key size limitation is an array of bytes.  The first byte describes the
+ * kind of limitation on the key size %$k$%; the rest are argument bytes
+ * %$a_i$%, for %$i \ge 0$%.  In all cases, %$a_0$% is the `recommended' key
+ * size.
+ *
+ *   * @KSZ_ANY@ means there is no restriction.
+ *
+ *   * @KSZ_RANGE@ requires that %$k \ge a_1$%, %$k \equiv 0 \pmod{a_3}$%,
+ *     and, if %$a_2 \ne 0$%, %$k \le a_2$%.
+ *
+ *   * @KSZ_SET@ requires that %$k \in {\,a_i\,}$%.
+ */
+
+enum {
+  KSZ_ANY,				/* Allows any key at all */
+  KSZ_RANGE,				/* Allows keys within a range */
+  KSZ_SET				/* Allows specific sizes of keys */
+};
+
+/* --- @keysz@ --- *
+ *
+ * Arguments:	@size_t sz@ = a proposed key size, or zero
+ *		@const octet *ksz@ = pointer to key size table
+ *
+ * Returns:	See below.
+ *
+ * Use:		Returns a sensible key size.  If @sz@ is nonzero, it is
+ *		interpreted as an amount (in bytes) of key material which the
+ *		caller has available, and the return value is either the
+ *		largest allowable key size less than or equal to the caller's
+ *		size, or zero if there is no valid key length small enough.
+ *		If @sz@ is zero, the function returns a `recommended' key
+ *		size.
+ */
+
+extern size_t keysz(size_t /*sz*/, const octet */*ksz*/);
+
+#define KSZ_CHECK(pre, sz) (keysz((sz), pre##_keysz) == (sz))
+#define KSZ_ASSERT(pre, sz)						\
+  assert(((void)"Bad key size for " #pre, KSZ_CHECK(pre, sz)))
+
 /*----- That's all, folks -------------------------------------------------*/
 
 #ifdef __cplusplus