diff --git a/tech/Bloom_filter.wiki b/tech/Bloom_filter.wiki
new file mode 100644
index 0000000..c181c58
--- /dev/null
+++ b/tech/Bloom_filter.wiki
@@ -0,0 +1,13 @@
+= Bloom filter =
+
+A bloom filter is a space efficient data structure that can test if an element
+is part of a set *false positives are possible*, however false negatives are
+not. Meaning it can return,
+
+* Possibly in the set
+* Definitly not in the set
+
+== Implementation ==
+
+* Simple [[hash_table]] set
+* 
diff --git a/tech/algorithms.wiki b/tech/algorithms.wiki
index 984221e..e44560d 100644
--- a/tech/algorithms.wiki
+++ b/tech/algorithms.wiki
@@ -21,9 +21,14 @@ Different ways to store and operate on data, with differing efficiency
 * [[splay_tree|Splay Tree]]
 * [[avl_tree|AVL Tree]]
 * [[kd_tree|KD Tree]]
-* [[Heap]] 
+* [[Heap]]
   - [[Fibonacci_heap]]
 
+== Probabilistic Data Structures ==
+
+* [[Bloom_filter]]
+
+
 == Common Algorithms ==
 
 === Graph and Tree ===
diff --git a/tech/digital_authentication.wiki b/tech/digital_authentication.wiki
index 8bc47b6..23c404b 100644
--- a/tech/digital_authentication.wiki
+++ b/tech/digital_authentication.wiki
@@ -33,5 +33,3 @@ Derived requirements from this,
 
 
 
-
-
diff --git a/tech/unix_password.wiki b/tech/unix_password.wiki
index 043391f..c790099 100644
--- a/tech/unix_password.wiki
+++ b/tech/unix_password.wiki
@@ -17,7 +17,13 @@
 == Improvements ==
 
 * Use MD5 hash
-* 48 bit salt
-* password length is unlimited
-* 128bit hash
-* Uses inner loop with 1000 iterations
+  * 48 bit salt
+  * password length is unlimited
+  * 128bit hash
+  * Uses inner loop with 1000 iterations
+* OpenBSD uses Blowfish based hash called Bcrypt
+  * Most secure unix hash/salt scheme
+  * uses 128bit salt to make 192bit hash value
+* Use a shadow password file
+  * separate file with hash; different file with ID
+