I need to come up with an Android app using Android studio that that encrypts messages using a simple substitution cipher.

Entry Text: message to be encoded.

This input should be a non$-$empty string and must contain at least one letter or number.

This input should be provided to the app through an EditText widget, initially blank.

Case $1$: first encryption parameter.

This input should be an integer coprime to $62$ between $0$ and $62$: $1,3,5,7,9,11,13,15,...61$

This input should be provided to the app through an EditText widget, initially set to $\text{'}1\text{'}.$

Statement$2$: second encryption parameter.

This input should be an integer $>=1$ and

This input should be provided to the app through an EditText widget, initially set to $\text{'}1\text{'}.$

Example:

Text Encrypted, the text resulting from applying the following cipher:

Each character in the alphabet is assigned a numeric value between $0$ and $61$ based on its position in the alphabet $($i$.$e$.,"0"=0,"1"=1,...,"9"=9,"$A$"=10,"$B$"=11,...,"$Z$"=35,"$a$"=36,"$b$"=37,...,"$z$"=61).$ Note that the alphabet contains letters and numbers.

For each character in the alphabet, where the numeric value is x$,$ the encoded value of the letter is defined as E$($x$)=($ax $+$ b$)\%62$ where a and b are the values of Arg Input $1$ and Arg Input $2$ respectively, as in an Affine Cipher.

The encoded character for the input character is calculated by taking the encoded number, which is a value between $0$ and $61,$ and translating it back into a character $($again$,$ where $"0"=0,"1"=1,...,"9"=9,"$A$"=10,"$B$"=11,...,"$Z$"=35,"$a$"=36,"$b$"=37,...,"$z$"=61).$

All non$-$alphanumeric characters must remain unchanged.

The output should be shown using a non$-$editable TextView that is initially blank and $($re$)$computed when the "Encrypt Entry Text" button is pressed. If any input is invalid when the button is pressed, the output should then be set to $""($i$.$e$.,$ the empty string$),$ and all applicable error messages should be generated $($see below$).$

The sample is included below