i was thinked about problem of Cyrpto.

At first glance, it looks like a simple classic password problem, but there are a lot of difficulties to think about the way the two encryption schemes are mixed.


The process is as follows.
First, create a substitution table for 26 alphabets.

Second, we select two key values for the shift cipher.

For example, the substitution table looks like this, and the key value of shift cipher is (3,7).

    Original..  : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
    Substitution: N E O B F M D Q V P U A W R I K Y J C S Z L G T X H 

Plain Text : "APPLE"

first, The letter corresponding to 'A' is N.

    cipher : APPLE --> NPPLE

second, Shift key 3 shifts the shift table to the right, and then maps the table.

    Original..  : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
    shift table : T X H N E O B F M D Q V P U A W R I K Y J C S Z L G 

    cipher : APPLE --> NPPLE --> NWPLE


third, Shift key 7 shifts the shift table to the right, and then maps the table.

    Original..  : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
    shift table : Y J C S Z L G T X H N E O B F M D Q V P U A W R I K  

    cipher : APPLE --> NPPLE --> NWPLE --> NWMLE


forth, Shift key 3 shifts the shift table to the right, and then maps the table.

    Original..  : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
    shift table : R I K Y J C S Z L G T X H N E O B F M D Q V P U A W  

    cipher : APPLE --> NPPLE --> NWPLE --> NWMLE --> NWMXE

forth, Shift key 7 shifts the shift table to the right, and then maps the table.

    Original..  : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
    shift table : D Q V P U A W R I K Y J C S Z L G T X H N E O B F M 

    cipher : APPLE --> NPPLE --> NWPLE --> NWMLE --> NWMXE --> NWMXU

    

The resulting encrypted string is : 'APPLE' result cipher is 'NWMXU'.

I tried to use the matrix, and I tried to perform the frequency analysis after the offset calculation for 26 ^ 2 cases (676) because I thought that the shift range exceeded the rotation range of 26 is meaningless in the shift operation anyway.

However, it has never been solved easily. I would appreciate it if you could give me some advice.