Add challenge 4

6 files changed, 65 insertions, 21 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)
diff --git a/src/utils/ByteUtils.scala b/src/utils/ByteUtils.scala
index ffc2e20..2c51917 100644
--- a/src/utils/ByteUtils.scala
+++ b/src/utils/ByteUtils.scala
@@ -1,6 +1,6 @@
 package ixee.cryptopals.utils
 
-import ConversionUtils.tup
+import FunctionUtils.tup
 
 object ByteUtils {
   trait SizedNumeric[T] {
diff --git a/src/utils/ConversionUtils.scala b/src/utils/ConversionUtils.scala
index 09f3aab..f8935f2 100644
--- a/src/utils/ConversionUtils.scala
+++ b/src/utils/ConversionUtils.scala
@@ -1,6 +1,7 @@
 package ixee.cryptopals.utils
 
 import ByteUtils._
+import FunctionUtils._
 
 object ConversionUtils {
   def hexStr2Bytes(s: String): Seq[Byte] =
@@ -61,9 +62,6 @@ object ConversionUtils {
     def asBytes = s.toSeq.map(_.toByte)
   }
 
-  // Because doing (_ f _).tupled confuses the inferencer...
-  def tup[A, B, C](f: (A, B) => C): ((A, B)) => C = f.tupled
-
   // TODO: tailrec this, get rid of for
   def toByteSeq[T : SizedNumeric : BitOps](x: T): Seq[Byte] = {
     val buf = new Array[Byte](x.byteSize)
diff --git a/src/utils/FrequencyMap.scala b/src/utils/FrequencyMap.scala
index 0bea25c..fffdabe 100644
--- a/src/utils/FrequencyMap.scala
+++ b/src/utils/FrequencyMap.scala
@@ -1,6 +1,6 @@
 package ixee.cryptopals.utils
 
-import ConversionUtils.tup
+import FunctionUtils.tup
 
 class FrequencyMap(mapargs: Map[Char, Double]) {
   sealed trait DiffResult
@@ -14,7 +14,7 @@ class FrequencyMap(mapargs: Map[Char, Double]) {
     if (c.isLower)
       mappings.get(c)
     else                                    // TODO remove the bias here
-      mappings.get(c.toLower).map(_ * 0.002) // bias HARD against uppercase spam. should make this a per-map setting.
+      mappings.get(c.toLower).map(_ * 0.0002) // bias HARD against uppercase spam. should make this a per-map setting.
 
   def diff(other: FrequencyMap): Double = {
     // pseudoscience here
@@ -36,29 +36,30 @@ class FrequencyMap(mapargs: Map[Char, Double]) {
 
   // TODO: don't hardcode these..
   def diffAt(c: Char, charFreq: Double) =
-    c match {
-      case ' ' => 0
-      case '{' | '}' | '`' | '|' =>
+    Math.pow(c match {
+      case ' ' =>
+        squared(0.10 - charFreq)
+      case '{' | '}' | '`' | '|' | '^' =>
         squared(0.000001 - charFreq) // { } | and ` are very unlikely irl
       case '[' | ']' =>
-        squared(0.000002 - charFreq) // [ ] are more likely
-      case '"' | '\''=>
+        squared(0.0000015 - charFreq) // [ ] are more likely
+      case '"' | '\'' =>
         squared(0.00001 - charFreq) // " or ' are 100% unlikely 90% of the time
       case '~' | '+' | '=' | '<' | '>' | '/' | '\\' =>
-        squared(0.000004 - charFreq) // math is weird kids
+        squared(0.00000175 - charFreq) // math is weird kids
       case ';' | ':' | '-' | '*' | '(' | '&' | ')' | '_' =>
-        squared(0.000009 - charFreq) // getting into more common punctuation
+        squared(0.000003 - charFreq) // getting into more common punctuation
       case '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' =>
-        squared(0.00001 - charFreq) // numbers are KINDA uncommon
+        squared(0.000002 - charFreq) // numbers are KINDA uncommon
       case '$' | '%' | '#' | '@' | '!' =>
-        squared(0.00003 - charFreq) // more punctuation...
+        squared(0.00002 - charFreq) // more punctuation...
       case '.' | ',' =>
         squared(0.00007 - charFreq) // and the last of the punctuations
       case '\n' | '\r' =>
-        squared(0.0000002 - charFreq) // explicit \r \n is rare in freeform text.
+        squared(0.000001 - charFreq) // explicit \r \n is rare in freeform text.
       case _ =>
-        this.at(c).map(_ - charFreq).map(squared).getOrElse(0.0)
-    }
+        this.at(c).map(_ - charFreq).map(squared).getOrElse(0.4)
+    }, 0.5)
 
   def squared(x: Double) = x * x
 
diff --git a/src/utils/FunctionUtils.scala b/src/utils/FunctionUtils.scala
new file mode 100644
index 0000000..84c141b
--- /dev/null
+++ b/src/utils/FunctionUtils.scala
@@ -0,0 +1,10 @@
+package ixee.cryptopals.utils
+
+object FunctionUtils {
+  // Because doing (_ f _).tupled confuses the inferencer...
+  def tup[A, B, C](f: (A, B) => C): ((A, B)) => C = f.tupled
+
+  implicit class Compositor[A, B](f: A => B) {
+    def :|[C](g: B => C): A => C = f.andThen(g)
+  }
+}