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Character higher than "s" cannot be encrypted?

I made simple encryption and decryption methods by following this video: http://www.youtube.com/watch?v=8AID7DKhSoM&feature=g-hist however when it is implemented in my program, any character above "s" is encrypted to "? " and then decrypts to 3. This does not seem to happen in the textbook, although some of his characters increase by large numbers. So why is this happening? Btw here is an important part of my program:

public class crypt { public String encrypt(String pass){ String cryppass_string=""; int l= pass.length(); char ch; for (int i=0; i<l; i++){ ch= pass.charAt(i); ch+= 12; cryppass_string+= ch; } return cryppass_string; } public String decrypt (String cryppass_string){ String pass_string= ""; int l= cryppass_string.length(); char ch; for (int i=0; i<l; i++){ ch= cryppass_string.charAt(i); ch-= 12; pass_string += ch; } return pass_string; } }

Here is an example: a password ("astu") must be encrypted to be entered, this is done:

  char[] newpass= newPassField.getPassword(); char[] repass= rePassField.getPassword(); if(Arrays.equals( newpass , repass )) { if(number==1) { Login_info.McIntosh_custom_pwd= fileob.string_to_char(cryptob.encrypt(fileob.char_to_string(newpass))); fileob.evr_tofile(); }

In another class, McIntoshcrypted is declared as:

 McIntosh_custom_pwd= fileob.string_to_char(cryptob.decrypt(FileData[0]));

fileob is an object of class Files

cryptob is an object of the crypt class

 public class Files { File f= new File("Eng Dept.txt"); public Formatter x; public void openfile(){ try{ x= new Formatter ("Eng Dept.txt"); } catch (Exception error){ System.out.println("error"); } } public void writing(String towrite){ try{ String filename= "Eng Dept.txt"; String newLine = System.getProperty("line.separator"); FileWriter fw = new FileWriter(filename,true); fw.write(towrite); fw.write(newLine); fw.close(); } catch (Exception eror){ System.out.println("error"); } } public String reading_string(int linenum){ String readline= ""; String filename= "Eng Dept.txt"; int lineno; try{ FileReader fr= new FileReader(filename); BufferedReader br= new BufferedReader(fr); for (lineno=1; lineno<= 1000; lineno++){ if(lineno== linenum){ readline= br.readLine(); } else br.readLine(); } br.close(); } catch (Exception eror){ System.out.println("error"); } return readline; } public String char_to_string(char[] toconv){ int l= toconv.length; String converted= ""; for (int i=0; i<l; i++) { converted+= toconv[i]; } return converted; } public char[] string_to_char(String toconv){ int l= toconv.length(); char[] converted = new char[l]; for (int i= 0; i<l; i++) { converted[i]=toconv.charAt(i); } return converted; } public void evr_tofile() { f.delete(); openfile(); writing(char_to_string(Login_info.McIntosh_custom_pwd)); }

In the txt file "as ??" and result

 System.out.print(Login_info.McIntosh_custom_pwd);

- "as33". I hope I explained it correctly ...

edit: proven solution

 public String encrypt(String pass){ String cryppass_string=""; int l= pass.length(); int x=0; char ch; for (int i=0; i<l; i++){ ch= pass.charAt(i); x= ((ch - 32) + 12) % 126 + 32; ch = (char)x; cryppass_string+= ch; } return cryppass_string; } public String decrypt (String cryppass_string){ String pass_string= ""; int l= cryppass_string.length(); int x=0; char ch; for (int i=0; i<l; i++){ ch= cryppass_string.charAt(i); x= ch-32; ch= (char)x; if (ch < 0) x= ch+126; ch= (char)x; x= ch-12+32; ch= (char)x; pass_string += ch; } return pass_string; }
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1 answer

I assume that you output the values ​​to a text file (web page?) Using an operation that converts non-printable characters to ? then the decryption problem arises when you read it back. If you want to do this something like this, you will need to limit encryption to output only printed characters. One way to do this is to use modular arithmetic to ensure that your encrypted character is within the print set (ASCII 32 - ASCII 126). The code you have will be correctly converted if you read / write binary files, but do not output it as ASCII text.

Encrypt

 ch = (char)((ch - 32) + 12) % 126 + 32; // extended expression to show rebasing/modulus

Decrypt

 ch = ch - 32; if (ch < 0) ch = ch + 126; ch = ch - 12 + 32;
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