Add crack_caesar functionality

README.md

@@ -43,6 +43,12 @@ decrypt_caesar("Khoor, Zruog!", 3)
 
 Likewise, `decrypt_caesar` turns everything lower-case, but retains symbols.
 
+Automatically crack the same text:
+```julia
+crack_caesar("Khoor, Zruog!")
+# outputs ("hello, world!", 3)
+```
+
 ### Monoalphabetic cipher
 
 Encrypt the text "Hello, World!" with the same Caesar cipher, but

src/ClassicalCiphers.jl

@@ -9,7 +9,7 @@ include("vigenere.jl")
 include("solitaire.jl")
 
 export encrypt_monoalphabetic, decrypt_monoalphabetic,
-       encrypt_caesar, decrypt_caesar,
+       encrypt_caesar, decrypt_caesar, crack_caesar,
        encrypt_vigenere, decrypt_vigenere,
        encrypt_solitaire, decrypt_solitaire,
        string_fitness

src/caesar.jl

@@ -24,3 +24,16 @@ function decrypt_caesar(ciphertext, key::Integer)
   key = ((key-1) % 26) + 1
   lowercase(encrypt_caesar(ciphertext, 26-key))
 end
+
+"""
+Cracks the given ciphertext according to the Caesar cipher.
+Returns (plaintext, key::Integer), such that encrypt_caesar(plaintext, key)
+would return ciphertext.
+
+Converts the input to lowercase.
+"""
+function crack_caesar(ciphertext)
+  texts = [(decrypt_caesar(ciphertext,key), key) for key in 1:26]
+  texts = sort(texts, by=(x -> string_fitness(first(x))))
+  texts[end]
+end

test/caesar.jl

@@ -0,0 +1,8 @@
+using ClassicalCiphers
+using Base.Test
+
+@test encrypt_caesar("THIS CODE WAS INVENTED BY JULIUS CAESAR", 3) == "WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU"
+
+@test decrypt_caesar("WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU", 3) == "this code was invented by julius caesar"
+
+@test crack_caesar("WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU") == ("this code was invented by julius caesar", 3)

test/monoalphabetic.jl

@@ -9,7 +9,3 @@ using Base.Test
 @test decrypt_monoalphabetic("5@coD", Dict{Char, Char}('a' => '5', 'B' => '@', 'b' => 'o', 'D' => 'D')) == "aBcbD"
 
 @test decrypt_monoalphabetic("WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU", "DEFGHIJKLMNOPQRSTUVWXYZABC") == lowercase("THIS CODE WAS INVENTED BY JULIUS CAESAR")
-
-@test encrypt_caesar("THIS CODE WAS INVENTED BY JULIUS CAESAR", 3) == "WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU"
-
-@test decrypt_caesar("WKLV FRGH ZDV LQYHQWHG EB MXOLXV FDHVDU", 3) == lowercase("THIS CODE WAS INVENTED BY JULIUS CAESAR")

test/runtests.jl

@@ -1,6 +1,6 @@
 using ClassicalCiphers
 
-tests = ["vigenere", "monoalphabetic", "solitaire"]
+tests = ["vigenere", "monoalphabetic", "solitaire", "caesar"]
 
 println("Running tests:")
 
@@ -8,4 +8,4 @@ for t in tests
     test_fn = "$t.jl"
     println(" * $test_fn")
     include(test_fn)
-end
+end