X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=cipher%2Fvigenere.py;fp=cipher%2Fvigenere.py;h=f1cfe996c5bc1eb6e4c3fcb6bf1ac708f40a509b;hb=1c711fcaa683414ec34bea0ea29269483f498343;hp=362322d8c28dcefeb38a73281da234b5309d5158;hpb=3ee00aa6e241bad0efe7ec600c26bdbfda2a2c00;p=cipher-tools.git

diff --git a/cipher/vigenere.py b/cipher/vigenere.py
index 362322d..f1cfe99 100644
--- a/cipher/vigenere.py
+++ b/cipher/vigenere.py
@@ -44,6 +44,16 @@ beaufort_variant_encipher=vigenere_decipher
 beaufort_variant_decipher=vigenere_encipher
 
 
+def index_of_coincidence_scan(text, max_key_length=20):
+    """Finds the index of coincidence of the text, using different chunk sizes."""
+    stext = sanitise(text)
+    iocs = {}
+    for i in range(1, max_key_length + 1):
+        splits = every_nth(stext, i)
+        mean_ioc = sum(index_of_coincidence(s) for s in splits) / i
+        iocs[i] = mean_ioc
+    return iocs
+
 def vigenere_keyword_break_mp(message, wordlist=keywords, fitness=Pletters,
                               chunksize=500):
     """Breaks a vigenere cipher using a dictionary and frequency analysis.