From 39707fda6289740729bef8cb214a2bf3f555b86e Mon Sep 17 00:00:00 2001
From: Joey Hess <joeyh@joeyh.name>
Date: Sun, 7 Aug 2016 16:25:12 -0400
Subject: finish AES decryption puzzle implementation

---
 Cost.hs | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

(limited to 'Cost.hs')

diff --git a/Cost.hs b/Cost.hs
index c31c4f8..38b6e28 100644
--- a/Cost.hs
+++ b/Cost.hs
@@ -88,7 +88,7 @@ bruteForceLinearSearch :: Cost step -> CostCalc BruteForceOp t
 bruteForceLinearSearch stepcost e = 
 	castCost stepcost `raiseCostPower` reduceEntropy e 1
 
--- | Things that can be brute-forced expose a CostCalc.
+-- | Things that can be brute-forced track their CostCalc.
 class Bruteforceable t a where
 	getBruteCostCalc :: t -> CostCalc BruteForceOp a
 
@@ -96,22 +96,32 @@ class Bruteforceable t a where
 estimateBruteforceOf :: Bruteforceable t a => t -> Entropy a -> Cost BruteForceOp
 estimateBruteforceOf t e = getBruteCostCalc t e
 
--- | Estimate of cost of brute force attack using AWS Spot instances,
--- in US dollars.
---
+data DataCenterPrice = DataCenterPrice
+	{ instanceCpuCores :: Integer
+	, instanceCostPerHour :: Cents
+	}
+
 -- August 2016 spot pricing: 36 CPU core c4.8xlarge at 33c/hour
+spotAWS :: DataCenterPrice
+spotAWS = DataCenterPrice
+	{ instanceCpuCores = 36
+	, instanceCostPerHour = Cents 33
+	}
+
+-- | Estimate of cost of brute force attack using a datacenter.
 --
--- Note that less GPU time is available on these instances;
--- there are not 36 GPU cores. But for simplicity we assume there are
--- that many GPU cores. So, this underestimates the price to brute
--- force such operations.
-estimateAWSSpotAttack :: Cost BruteForceOp -> Dollars
-estimateAWSSpotAttack opcost = centsToDollars $ costcents
+-- Note that this assumes that CPU cores and GPU cores are of equal number,
+-- which is unlikely to be the case; typically there will be many more
+-- cores than GPUs. So, this underestimates the price to brute force
+-- operations which run faster on GPUs.
+estimateAttack :: DataCenterPrice -> Cost BruteForceOp -> Dollars
+estimateAttack dc opcost = centsToDollars $ costcents
   where
 	(Seconds cpuseconds) = fst (totalCost opcost)
 	cpuyears = cpuseconds `div` (60*60*24*365)
-	cpucores = 36
-	costpercpuyear = Cents (33*24*365 `div` cpucores)
+	costpercpuyear = Cents $
+		fromIntegral (instanceCostPerHour dc) * 24 * 365
+			`div` instanceCpuCores dc
 	costcents = Cents cpuyears * costpercpuyear
 
 newtype Cents = Cents Integer
-- 
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