2 files changed, 38 insertions, 3 deletions
diff --git a/src/solvers/Challenge4.scala b/src/solvers/Challenge4.scala
new file mode 100644
index 0000000..f71f6c0
--- /dev/null
+++ b/src/solvers/Challenge4.scala
@@ -0,0 +1,29 @@
+package ixee.cryptopals.solvers
+
+import scala.io.Source
+import ixee.cryptopals.utils.ByteUtils._
+import ixee.cryptopals.utils.ConversionUtils._
+import ixee.cryptopals.utils.FunctionUtils._
+import ixee.cryptopals.utils._
+
+object Challenge4 {
+  def findSingleCharacterXor(strings: Seq[Seq[Byte]]): (String, Int) = {
+    strings
+      .map(XorDecrypt.findBestSingleByteKey)
+      .zip(strings)
+      .zipWithIndex
+      .map { pair => (pair._1._1, pair._1._2, pair._2) }
+      .filter(_._1 != 0)
+      .map { triplet => (XorDecrypt.decryptToAscii(triplet._2)(triplet._1), triplet._3) }
+      .map { pair => (pair._1, TextScorer.score(pair._1.asBytes), pair._2) }
+      .sortBy(_._2)
+      .map { triplet => (triplet._1, triplet._3) }
+      .head
+  }
+
+  def run(inputFile: String) = {
+    findSingleCharacterXor(
+      Source.fromFile(inputFile).getLines().toSeq.map(hexStr2Bytes(_))
+    )
+  }
+}
diff --git a/src/solvers/XorDecrypt.scala b/src/solvers/XorDecrypt.scala
index b7f7c43..6b82c34 100644
--- a/src/solvers/XorDecrypt.scala
+++ b/src/solvers/XorDecrypt.scala
@@ -2,18 +2,24 @@ package ixee.cryptopals.solvers
 
 import ixee.cryptopals.utils._
 import ixee.cryptopals.utils.ByteUtils._
+import ixee.cryptopals.utils.FunctionUtils._
 
 object XorDecrypt {
   implicit val freq = Frequencies.cornell40kSample
 
-  def tryBestDecrypt(ciphertext: Seq[Byte]) = {
-    val key = findBestSingleByteKey(ciphertext)
+  def decryptToAscii(ciphertext: Seq[Byte])(key: Byte): String = {
     new String((ciphertext xor Stream.continually(key)).toArray)
   }
 
+  def tryBestDecrypt(ciphertext: Seq[Byte]): String = {
+    (findBestSingleByteKey _ :| decryptToAscii(ciphertext) _)(ciphertext)
+  }
+
   def findBestSingleByteKey(ciphertext: Seq[Byte]): Byte =
     candidates(ciphertext)
-      .minBy(_._1)._2.toByte
+      .reduceOption( (a: (Double, Int), b: (Double, Int)) =>
+        if (a._1 < b._1) a else b
+      ).map(_._2.toByte).getOrElse(0.toByte)
 
   def candidates(ciphertext: Seq[Byte]) =
     (0 until 256)