add entropy check for entered passphrases

configure.ac

@@ -360,6 +360,8 @@ AS_IF([test "x$enable_optimize" != "xno"], [
 
 CXXFLAGS="$CFLAGS"
 
+# FIXME: check for libm
+LIBS="$LIBS -lm"
 
 # conditionals for bindings and stuff
 

include/pcp/key.h

@@ -28,6 +28,10 @@
 #include <stdio.h>
 #include <time.h>
 
+#include <math.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
 #include "defines.h"
 #include "platform.h"
 #include "mem.h"
@@ -309,6 +313,8 @@ void pcp_dumppubkey(pcp_pubkey_t *k);
 */
 void pcpkey_setowner(pcp_key_t *key, char *owner, char *mail);
 
+double pcp_getentropy(char *source);
+
 #endif /*  _HAVE_PCP_KEYPAIR_H */
 
 /**@}*/

libpcp/key.c

@@ -543,3 +543,38 @@ void pcp_dumppubkey(pcp_pubkey_t *k) {
 
   printf("     type: 0x%02X\n", k->type);
 }
+
+
+/*
+  via 
+  http://rosettacode.org/wiki/Entropy#C
+*/
+double pcp_getentropy(char *source) {
+  int len;
+  int *hist;
+  double H;
+  int wherechar[256];
+  int i,histlen;
+  
+  histlen = 0;
+  H = 0;
+  len = (int)strlen(source);
+  hist = (int*)calloc(len, sizeof(int));
+
+  for(i=0; i<256; i++)
+    wherechar[i] =- 1;
+  
+  for(i=0; i<len; i++){
+    if(wherechar[(int)source[i]] == -1) {
+      wherechar[(int)source[i]] = histlen;
+      histlen++;
+    }
+    hist[wherechar[(int)source[i]]]++;
+  }
+
+  for(i=0; i<histlen; i++) {
+    H -= (double)hist[i] / len * log2((double)hist[i] / len);
+  }
+  
+  return H;
+}

src/keymgmt.c

@@ -82,12 +82,16 @@ void pcp_keygen(char *passwd) {
 		 "Enter the passphrase again", 1, NULL);
   }
   else {
-    passphrase = ucmalloc(strlen(passwd)+1);
-    memcpy(passphrase, passwd, strlen(passwd)+1);
+    passphrase = passwd;
   }
 
-  if(strnlen(passphrase, 1024) > 0)
+  if(strnlen(passphrase, 1024) > 0) {
+    double ent = pcp_getentropy(passphrase);
+    if(ent < 3) {
+      fprintf(stderr, "WARNING: you are using a weak passphrase (entropy: %lf)\n", ent);
+    }
     key = pcpkey_encrypt(ptx, k, passphrase);
+  }
   else {
     char *yes = pcp_getstdin("WARNING: secret key will be stored unencrypted. Are you sure [yes|NO]?");
     if(strncmp(yes, "yes", 1024) == 0)
@@ -108,6 +112,11 @@ void pcp_keygen(char *passwd) {
     }
   }
 
+  if(passwd == NULL) {
+    /* if passwd is set, it'll be free'd in main() */
+    sfree(passphrase);
+  }
+  
  errkg1:
   free(mail);
   free(owner);