add check for that the word size is 2-potent

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/src/libkeccak/spec.h b/src/libkeccak/spec.h
index c72c04d..bc5f6c3 100644
--- a/src/libkeccak/spec.h
+++ b/src/libkeccak/spec.h
@@ -20,6 +20,9 @@
 #define LIBKECCAK_SPEC_H  1
 
 
+#include <limits.h>
+
+
 /**
  * Message suffix for SHA3 hashing
  */
@@ -62,7 +65,7 @@
 #define LIBKECCAK_SPEC_ERROR_OUTPUT_NONPOSITIVE  5
 
 /**
- * Invalid `libkeccak_spec_t` values:  `.bitrate + `.capacity`
+ * Invalid `libkeccak_spec_t` values: `.bitrate + `.capacity`
  * is greater 1600 which is the largest supported state size
  */
 #define LIBKECCAK_SPEC_ERROR_STATE_TOO_LARGE  6
@@ -73,6 +76,12 @@
  */
 #define LIBKECCAK_SPEC_ERROR_STATE_MOD_25  7
 
+/**
+ * Invalid `libkeccak_spec_t` values: `.bitrate + `.capacity`
+ * is a not a 2-potent multiple of 25
+ */
+#define LIBKECCAK_SPEC_ERROR_WORD_NON_2_POTENT  8
+
 
 
 /**
@@ -150,7 +159,7 @@ void libkeccak_spec_rawshake(libkeccak_spec_t* restrict spec, long x, long d)
 static inline __attribute__((nonnull, nothrow, unused, warn_unused_result, pure))
 int libkeccak_spec_check(const libkeccak_spec_t* restrict spec)
 {
-  long state_size = spec->capacity + spec->bitrate;
+  long state_size = spec->capacity + spec->bitrate, n_state_size;
   if (spec->bitrate <= 0)   return LIBKECCAK_SPEC_ERROR_BITRATE_NONPOSITIVE;
   if (spec->bitrate % 8)    return LIBKECCAK_SPEC_ERROR_BITRATE_MOD_8;
   if (spec->capacity <= 0)  return LIBKECCAK_SPEC_ERROR_CAPACITY_NONPOSITIVE;
@@ -158,6 +167,14 @@ int libkeccak_spec_check(const libkeccak_spec_t* restrict spec)
   if (spec->output <= 0)    return LIBKECCAK_SPEC_ERROR_OUTPUT_NONPOSITIVE;
   if (state_size > 1600)    return LIBKECCAK_SPEC_ERROR_STATE_TOO_LARGE;
   if (state_size % 25)      return LIBKECCAK_SPEC_ERROR_STATE_MOD_25;
+  state_size /= 25;
+  
+  /* This is a portable implementation of `(x & -x) != x` which assumes
+   * two's complement, which of course is always satisfied by GCC, but anyway... */
+  n_state_size = ((~state_size) ^ (LONG_MIN & ~LONG_MAX)) + 1;
+  if ((state_size & n_state_size) != state_size)
+    return LIBKECCAK_SPEC_ERROR_WORD_NON_2_POTENT;
+  
   return 0;
 }