Kosaki (2015-07-15)

Vigenere cipher.

Kosaki implements the Vigenere cipher.  Use uppercase keys to encrypt:

   perl KEY plaintext.txt > ciphertext.txt

Use lowercase keys to decrypt:

   perl key ciphertext.txt > plaintext.txt

Mixed case is OK, just use opposite case for decryption:

   perl KeY plaintext.txt | perl kEy > same.txt

Note that non-alpha characters are passed from input to output as is,
which may leave hints about what the original encrypted text was.
Marika will remove unrelated characters for you:

   perl marika | perl - input.txt > stripped.txt

Lost your key?  Chitoge will break the key for you:

   perl chitoge | perl - ciphertext.txt > keys.txt

Chitoge will output an uppercase and a lowercase key, both are
equivalent.  Depending on whether encryption was done with uppercase
or lowercase keys, one of the output will be more recognizable than
the other.  Chitoge doesn't always succeed, certain criteria about the
input must be met:

   - Original text is English.
   - Key length is at most 64 characters.
   - Ciphertext is at least ~100 times longer than encryption key length.

Consult this page for expected success rates:

Template based on Onodera Kosaki from Nisekoi.

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