From: mdw <mdw>
Date: Sat, 17 Jun 2000 11:27:52 +0000 (+0000)
Subject: Key size table interpretation.
X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/commitdiff_plain/7809fc3d2f3ee3aa0bca61f875492292d4db22a3

Key size table interpretation.
---

diff --git a/keysz.c b/keysz.c
new file mode 100644
index 0000000..7a2a794
--- /dev/null
+++ b/keysz.c
@@ -0,0 +1,91 @@
+/* -*-c-*-
+ *
+ * $Id: keysz.c,v 1.1 2000/06/17 11:27:52 mdw Exp $
+ *
+ * General block cipher utilities
+ *
+ * (c) 2000 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------* 
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ * 
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Revision history --------------------------------------------------* 
+ *
+ * $Log: keysz.c,v $
+ * Revision 1.1  2000/06/17 11:27:52  mdw
+ * Key size table interpretation.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <assert.h>
+
+#include "gcipher.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @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.
+ */
+
+size_t keysz(size_t sz, const octet *ksz)
+{
+  if (sz == 0)
+    return (ksz[1]);
+  else switch (ksz[0]) {
+    case KSZ_ANY:
+      return (sz);
+    case KSZ_RANGE:
+      if (ksz[4])
+	sz -= sz % ksz[4];
+      if (sz < ksz[2])
+	return (0);
+      if (ksz[3] && sz > ksz[3])
+	return (ksz[3]);
+      return (sz);
+    case KSZ_SET: {
+      unsigned q = 0;
+      for (ksz++; *ksz; ksz++) {
+	if (sz >= *ksz && q < *ksz)
+	  q = *ksz;
+      }
+      return (q);
+    }
+  }
+
+  assert(((void)"bad key size table", 0));
+  return (0);
+}
+
+/*----- That's all, folks -------------------------------------------------*/