Add Affine functionality - encrypt, decrypt, crack

README.md

@@ -50,6 +50,37 @@ crack_caesar("Khoor, Zruog!")
 # outputs ("hello, world!", 3)
 ```
 
+### Affine cipher
+
+Encrypt the text "Hello, World!" with the function `x -> 3x+4`:
+
+```julia
+encrypt_affine("Hello, World!", 3, 4)
+# outputs
+```
+
+Notice that `encrypt_affine` turns everything upper-case, but retains symbols.
+The multiplier is the second argument, and the additive constant is the third.
+
+The multiplier must be coprime to 26, or an error is thrown.
+
+Decrypt the same text:
+
+```julia
+decrypt_affine("ZQLLU, SUDLN!", 3, 4)
+# outputs "hello, world!"
+```
+
+Crack the same text:
+
+```julia
+crack_affine("ZQLLU, SUDLN!")
+# outputs ((3, 4), "hello, world!")
+```
+
+You can provide `mult=` or `add=` options to `crack_affine`, if they are known,
+to help it out.
+
 ### Monoalphabetic cipher
 
 Encrypt the text "Hello, World!" with the same Caesar cipher, but

REQUIRE

@@ -1 +1,2 @@
 julia 0.4
+Iterators

src/ClassicalCiphers.jl

@@ -8,9 +8,11 @@ include("caesar.jl")
 include("vigenere.jl")
 include("solitaire.jl")
 include("portas.jl")
+include("affine.jl")
 
 export encrypt_monoalphabetic, decrypt_monoalphabetic, crack_monoalphabetic,
        encrypt_caesar, decrypt_caesar, crack_caesar,
+       encrypt_affine, decrypt_affine, crack_affine,
        encrypt_vigenere, decrypt_vigenere, crack_vigenere,
        encrypt_portas, decrypt_portas,
        encrypt_solitaire, decrypt_solitaire,

src/affine.jl

@@ -0,0 +1,65 @@
+using Iterators
+
+"""
+Encrypts the given plaintext according to the Affine cipher.
+The key is given as a pair of integers: first the multiplier, then
+the additive constant.
+
+The multiplier must be coprime to 26. If it is not, an error is thrown.
+
+Converts the input to uppercase, but retains symbols.
+
+Optional argument: offset=0, which specifies what number 'a' should be
+considered as.
+"""
+function encrypt_affine(plaintext, mult::Integer, add::Integer; offset=0)
+	if mult % 2 == 0 || mult % 13 == 0
+		error("Multiplier must be coprime to 26.")
+	end
+
+	keystr = join([Char(((mult*i + add) % 26) + 97 - offset) for i in offset:25+offset], "")
+    encrypt_monoalphabetic(plaintext, keystr)
+end
+
+"""
+Decrypts the given ciphertext according to the Affine cipher.
+The key is given as a pair of integers: first the multiplier, then
+the additive constant.
+
+The multiplier must be coprime to 26. If it is not, an error is thrown.
+
+Converts the input to lowercase, but retains symbols.
+
+Optional argument: offset=0, which specifies what number 'a' should be
+considered as.
+"""
+function decrypt_affine(ciphertext, mult::Integer, add::Integer; offset=0)
+	if mult % 2 == 0 || mult % 13 == 0
+		error("Multiplier must be coprime to 26.")
+	end
+
+	keystr = join([Char(((mult*i + add) % 26) + 97 - offset) for i in offset:25+offset], "")
+	decrypt_monoalphabetic(ciphertext, keystr)
+end
+
+"""
+Cracks the given ciphertext according to the Affine cipher.
+Returns ((multiplier, additive constant), decrypted string).
+
+Converts the input to lowercase, but retains symbols.
+
+Optional arguments: mult=0, which specifies the multiplier if known;
+add=-1, which specifies the additive constant if known.
+"""
+function crack_affine(ciphertext; mult=0, add=-1)
+	mults = mult != 0 ? [mult] : [i for i in filter(x -> (x % 2 != 0 && x % 13 != 0), 1:25)]
+	adds = add != -1 ? [add] : (0:25)
+
+	possible_keys = product(mults, adds)
+
+	decrypts = [(i, decrypt_affine(ciphertext, i[1], i[2])) for i in possible_keys]
+
+	sort!(decrypts, by=(x -> string_fitness(x[2])))
+
+	decrypts[end]
+end

test/affine.jl

@@ -0,0 +1,22 @@
+using ClassicalCiphers
+using Base.Test
+
+# docs examples
+
+@test encrypt_affine("Hello, World!", 3, 4) == "ZQLLU, SUDLN!"
+@test decrypt_affine("ZQLLU, SUDLN!", 3, 4) == "hello, world!" 
+@test crack_affine("zqllu, sudln!") == ((3, 4), "hello, world!")
+
+# Wikipedia examples
+
+@test encrypt_affine("affine cipher", 5, 8) == "IHHWVC SWFRCP"
+@test decrypt_affine("IHHWVC SWFRCP", 5, 8) == "affine cipher"
+
+# Practical Cryptography
+
+@test encrypt_affine("defend the east wall of the castle", 5, 7) == uppercase("wbgbuw yqb bhty nhkk zg yqb rhtykb")
+@test decrypt_affine("wbgbuwyqbbhtynhkkzgyqbrhtykb", 5, 7) == "defendtheeastwallofthecastle"
+@test crack_affine("wbgbuwyqbbhtynhkkzgyqbrhtykb") == ((5, 7), "defendtheeastwallofthecastle")
+
+@test crack_affine("wbgbuwyqbbhtynhkkzgyqbrhtykb", mult=5) == ((5, 7), "defendtheeastwallofthecastle")
+@test crack_affine("wbgbuwyqbbhtynhkkzgyqbrhtykb", add=7) == ((5, 7), "defendtheeastwallofthecastle")

test/runtests.jl

@@ -1,6 +1,6 @@
 using ClassicalCiphers
 
-tests = ["vigenere", "monoalphabetic", "solitaire", "caesar", "portas"]
+tests = ["vigenere", "monoalphabetic", "solitaire", "caesar", "portas", "affine"]
 
 println("Running tests:")