basic password entropy calculation

1 files changed, 15 insertions, 1 deletions

diff --git a/Cost.hs b/Cost.hs
index de5a82d..3c7c21d 100644
--- a/Cost.hs
+++ b/Cost.hs
@@ -2,9 +2,13 @@
 
 module Cost where
 
+import Types
+import Entropy
 import Utility.HumanTime
 import Data.Monoid
 
+import qualified Data.ByteString.UTF8 as B
+
 -- | An estimated cost to perform an operation.
 data Cost op 
 	= CPUCost Seconds
@@ -61,7 +65,7 @@ type CostCalc op t = Entropy t -> Cost op
 
 -- | Number of bits of entropy
 newtype Entropy t = Entropy Int
-	deriving (Num)
+	deriving (Num, Show)
 
 -- | Entropy can never go negative when subtracting bits from it.
 reduceEntropy :: Entropy t -> Int -> Entropy t
@@ -70,6 +74,16 @@ reduceEntropy (Entropy a) b = Entropy (max 0 (a - b))
 -- | Things that can have entropy
 data UnknownPassword
 
+-- | Naive calculation of the entropy of a password.
+-- Does not take common passowrds and password generation patterns into
+-- account, so this is an overestimation of how hard a password
+-- is to crack.
+passwordEntropy :: Password -> Entropy UnknownPassword
+passwordEntropy (Password p) = Entropy $ floor $
+	entropy s * fromIntegral (length s)
+  where
+	s = B.toString p
+
 -- | CostCalc for a brute force linear search through an entropy space
 -- in which each step entails paying a cost.
 --