init

html/tasks/chapter_5/task12_encryption/script.js

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+var encForm = document.getElementById("encrypt");
+var emess = document.getElementById("emess");
+var eciph = document.getElementById("enum");
+var etext = document.getElementById("etext");
+encForm.onsubmit=function(evt){
+    evt.preventDefault();
+    etext.innerHTML = encrypt(emess.value, parseInt(eciph.value));
+}
+
+var decForm = document.getElementById("decrypt");
+var dmess = document.getElementById("dmess");
+var dciph = document.getElementById("dnum");
+var dtext = document.getElementById("dtext");
+decForm.onsubmit=function(evt){
+    evt.preventDefault();
+    dtext.innerHTML = decrypt(dmess.value, parseInt(dciph.value));
+}
+
+function mod(x,n){
+    return ((x%n)+n)%n;
+}
+
+
+function encrypt(mess,number){
+    messArray=mess.split('');
+    result=[];
+
+    for (i in messArray){
+        x=messArray[i].charCodeAt(0);
+
+        if (x>64 && x<91){
+            x-=64;
+            x+=number;
+            x=mod(x,26);
+            x+=64;
+        } else if (x>96 && x<123){
+            x-=96;
+            x+=number;
+            x=mod(x,26);
+            x+=96;
+        }
+        result.push(String.fromCharCode(x));
+    }
+    result = result.join("");
+    return result;
+
+}
+
+function decrypt(mess,number){
+    messArray=mess.split('');
+    result=[];
+
+    for (i in messArray){
+        x=messArray[i].charCodeAt(0);
+
+        if (x>64 && x<91){
+            x-=64;
+            x-=number;
+            x=mod(x,26);
+            x+=64;
+        } else if (x>96 && x<123){
+            x-=96;
+            x-=number;
+            x=mod(x,26);
+            x+=96;
+        }
+        result.push(String.fromCharCode(x));
+    }
+    result = result.join("");
+    return result;
+}