c++ - c encrypt decrypt not working as expected -


i trying implement encode , decode of string based on page

http://www.thecrazyprogrammer.com/2016/11/caesar-cipher-c-c-encryption-decryption.html

and here code,

string encryptstring(string message){      int i, key=95828205;     char ch;     for(i = 0; message[i] != '\0'; ++i){             ch = message[i];              if(ch >= 'a' && ch <= 'z'){                 ch = ch + key;                  if(ch > 'z'){                     ch = ch - 'z' + 'a' - 1;                 }                  message[i] = ch;             }             else if(ch >= 'a' && ch <= 'z'){                 ch = ch + key;                  if(ch > 'z'){                     ch = ch - 'z' + 'a' - 1;                 }                  message[i] = ch;             }         }       printf("encrypted message: %s", message);       return message; }  string  decryptstring(string message){       int i, key=95828205;      char ch;     for(i = 0; message[i] != '\0'; ++i){             ch = message[i];              if(ch >= 'a' && ch <= 'z'){                 ch = ch - key;                  if(ch < 'a'){                     ch = ch + 'z' - 'a' + 1;                 }                  message[i] = ch;             }             else if(ch >= 'a' && ch <= 'z'){                 ch = ch - key;                  if(ch < 'a'){                     ch = ch + 'z' - 'a' + 1;                 }                  message[i] = ch;             }         }       printf("decrypted message: %s", message);      return message; }

and called function like,

string msg="test.com",msg1,msg2; msg1 = encryptstring(msg); msg2 = decryptstring(msg1);

but getting random character while decrypt data

you have defined

key=95828205;

then add character array , store array

if(ch >= 'a' && ch <= 'z'){      ch = ch + key;      message[i] = ch;      ...

and means character has overflowed , there random number.

then if try check (in encrypt)

 if(ch >= 'a' && ch <= 'z'){       ch = ch - key;

there isn't high change value in interval.

to do

you should swap these lines (first real letter , compare it)

 ch = ch - key;  if(ch >= 'a' && ch <= 'z'){       ...

and use key wont cause char overflow (e.g. 5)

edit

test after changes

input

message: test key:     5

output encrypt

yjxy

output decrypt

test

Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more