DB user verify Function Implementation

   CREATE OR REPLACE FUNCTION "SYS"."DBUSER_VERIFY_FUNCTION"
(username varchar2,
   password varchar2,
   old_password varchar2)
   RETURN boolean IS
   n boolean;
   m integer;
   differ integer;
   isdigit boolean;
   ischar  boolean;
   digitarray varchar2(20);
   chararray varchar2(52);
   specchararray varchar2(4);

BEGIN
  digitarray:= '0123456789';
  chararray:= 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  specchararray:= '_#';

--Check if the password is the same as the username
IF password = username THEN
   raise_application_error(-20001, 'Password matches username');
END IF;

--Check for the minimum length of the password
IF length(password) < 8 THEN
   raise_application_error(-20002, 'Password length less than 8');
END IF;

--Check if the password is too simple
IF NLS_LOWER(password) IN ('hellotune', 'password', 'abcd1234', 'developer',
   'computer', 'india', 'newsland', 'wasington')
   THEN raise_application_error(-20003, 'Password too simple');
END IF;

--Check if password contains at least one letter and one digit
--1. Check for digit
isdigit:=FALSE;
m := length(password);
FOR i IN 1..10 LOOP
  FOR j IN 1..m LOOP
    IF substr(password,j,1) = substr(digitarray,i,1) THEN
      isdigit:=TRUE;
       GOTO findchar;
    END IF;
  END LOOP;
END LOOP;
IF isdigit = FALSE THEN
  raise_application_error(-20004, 'Password should contain at least one \
  digit and one character and one special character');
END IF;
--2. Check for character
<>
ischar:=FALSE;
FOR i IN 1..length(chararray) LOOP
  FOR j IN 1..m LOOP
    IF substr(password,j,1) = substr(chararray,i,1) THEN
      ischar:=TRUE;
       GOTO findspecchar;
      END IF;
    END LOOP;
END LOOP;
IF ischar = FALSE THEN
  raise_application_error(-20004,'Password should contain at least one \
    digit and one character and one special character');
END IF;
--3. Check for special character
<>
ischar:=FALSE;
FOR i IN 1..length(specchararray) LOOP
  FOR j IN 1..m LOOP
    IF substr(password,j,1) = substr(specchararray,i,1) THEN
      ischar:=TRUE;
       GOTO endsearch;
      END IF;
    END LOOP;
END LOOP;
IF ischar = FALSE THEN
  raise_application_error(-20004,'Password should contain at least one \
    digit and one character and one special character');
END IF;

<>
--Check if the password differs from the previous password by at least 3 letters

IF old_password = '' THEN
raise_application_error(-20005, 'Old password is null');
END IF;
--Everything is fine return TRUE;
differ:= length(old_password) - length(password);
IF abs(differ) < 3 THEN
  IF length(password) < length(old_password) THEN
    m := length(password);
  ELSE
    m := length(old_password);
  END IF;
  differ :=abs(differ);
  FOR i IN 1..m LOOP
    IF substr(password,i,1) != substr(old_password,i,1) THEN
       differ := differ + 1;
    END IF;
  END LOOP;
  IF differ < 3 THEN
    raise_application_error(-20006, 'Password should differ by at least \
    3 characters');
  END IF;
END IF;
--Everything is fine return TRUE;
RETURN (TRUE);
END;