# HG changeset patch
# User Claus Gittinger <cg@exept.de>
# Date 1412264178 -7200
# Node ID bfae9f81787a649c30b278f972c71ab27f42e61b
# Parent  5afe23725daf683b257bb811e8b5605e9f3a18e3
class: Random
changed: #randomSeed
sv's idea: feed hash instead of xoring the individual entropy sources

diff -r 5afe23725daf -r bfae9f81787a Random.st
--- a/Random.st	Thu Oct 02 17:19:47 2014 +0200
+++ b/Random.st	Thu Oct 02 17:36:18 2014 +0200
@@ -268,50 +268,41 @@
      The entropy returned should be reasonable enough for a good seed of a good rnd
      generator. However, keep in mind, that it only has a limited number of entropy bits
      (in the order of 32). 
-     But it shoud be much better than what is commonly used in older
+     But it should be much better than what is commonly used in older
      programs (current time) or even a constant."
 
-    |newSeed hash|
+    |hash|
+
+    hash := MD5Stream new.
 
     RandomSalt isNil ifTrue:[
         RandomSalt := 1.
     ] ifFalse:[
         RandomSalt := RandomSalt + 1.
     ].
-    newSeed := RandomSalt + (Time microsecondClockValue bitXor:OperatingSystem getProcessId).
-    newSeed := newSeed bitXor:(ObjectMemory addressOf:(Object new)).
-    newSeed := newSeed bitXor:(ObjectMemory oldSpaceUsed).
+    hash nextPut:RandomSalt.
+    hash nextPutAll:Time microsecondClockValue asLargeInteger digitBytes. 
+    hash nextPutAll:OperatingSystem getProcessId asLargeInteger digitBytes. 
+    hash nextPutAll:(ObjectMemory addressOf:(Object new)) asLargeInteger digitBytes. 
+    hash nextPutAll:(ObjectMemory oldSpaceUsed) asLargeInteger digitBytes. 
+    hash nextPutAll:(ObjectMemory newSpaceUsed) asLargeInteger digitBytes. 
     [
-        newSeed := newSeed bitXor:(OperatingSystem getCPUCycleCount).
+        hash nextPutAll:(OperatingSystem getCPUCycleCount) asLargeInteger digitBytes. 
     ] on:PrimitiveFailure do:[].
 
-    "/ any other easy sources of entropy?
-
-    "/ how likely is that? - paranoia
-    newSeed = 0 ifTrue:[ newSeed := Time microsecondClockValue ]. 
-
-    "/ The above gives us a 5-8 byte number, but some high bits are constant.
-    "/ (the constant high bits from the above do not provide any entropy)
-    "/ so the effective entropy is more in the order of 32 bits.
-    "/ if called shortly in a row, the returned values are only affected by
-    "/ the amount of memory allocated in between (and if there are any newspace reclamations),
-    "/ the real time in between and the number of cpu cycles between,
-    "/ plus the salt counter.
-    "/ Hashing should make this less likely to be predicted.
+    "/ any other cheap sources of entropy?
 
     "/ I think there is no problem in that MD5 is not a secure hash algo here - the idea is to shuffle the bits around a bit
     "/ (because the numbers above usually have many high bits in common)
     "/ and then condense the bits into a smaller number.
     "/ Any comment from a crypto guy here - I am willing to change this to some other hash, if that makes a problem
 
-    hash := MD5Stream hashValueOf:(newSeed asLargeInteger digitBytes).
-    "/ still the same number of entropy bits, bit no longer limited to an unknown number of low bits,
-    "/ bit arbitrarily spread among the hash bytes.
-    "/ Seeding rnd generators should Xor the returned 8 bytes to their max. seed size
-    ^ LargeInteger digitBytes:hash.
+    "/ Seeding rnd generators should take some bits from the returned number (i.e. their max. seed size)
+    ^ LargeInteger digitBytes:hash hashValue.
 
     "
      10 timesRepeat:[Transcript showCR:self randomSeed].
+     10 timesRepeat:[Transcript showCR:(self randomSeed bitAnd:16rFFFF)].
      self randomSeed bitAnd:16rFFFFFFFF
     "
 ! !
@@ -766,10 +757,10 @@
 !Random class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic2/Random.st,v 1.55 2014-10-02 14:50:55 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic2/Random.st,v 1.56 2014-10-02 15:36:18 cg Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic2/Random.st,v 1.55 2014-10-02 14:50:55 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic2/Random.st,v 1.56 2014-10-02 15:36:18 cg Exp $'
 ! !