Case Sensitive Password

Passwords have become case sensitive from Oracle 11g onwards.
In Earlier releases password was not case sensitive.
The case sensitive feature is default feature for Oracle 11g databases. Of course this feature can be enabled/disabled with an initialization parameter SEC_CASE_SENSITIVE_LOGON

SQL> SHOW PARAMETER SEC_CASE_SENSITIVE_LOGON

NAME                                 TYPE        VALUE
------------------------------------ ----------- ----------------------------
sec_case_sensitive_logon             boolean     TRUE

SQL> ALTER SYSTEM SET SEC_CASE_SENSITIVE_LOGON = FALSE;
System altered.

The case sensitive password functionality can be seen below.

SEC_CASE_SENSITIVE_LOGON initialization parameter is TRUE and creates a new user with a mixed case password.
CONN / AS SYSDBA
SQL> SHOW PARAMETER SEC_CASE_SENSITIVE_LOGON
NAME                                 TYPE        VALUE
------------------------------------ ----------- ----------------------------
sec_case_sensitive_logon             boolean     TRUE
SQL> CREATE USER testuser IDENTIFIED BY TestUser;
SQL> GRANT CONNECT TO testuser;

2. Trying to connect using different case passwords.

SQL> CONN testuser/TestUser
Connected.
SQL> CONN testuser/testuser
ERROR:
ORA-01017: invalid username/password; logon denied
Warning: You are no longer connected to ORACLE.
SQL>

3. Changing the parameter SEC_CASE_SENSITIVE_LOGON to FALSE and we can connect.

CONN / AS SYSDBA
ALTER SYSTEM SET SEC_CASE_SENSITIVE_LOGON = FALSE;
SQL> CONN testuser/TestUser
Connected.
SQL> CONN testuser/TESTUSER
Connected.
SQL>

An important point is that even when case sensitive passwords are not enabled, the original case of the password when it was created/modified is retained. Which means that the passwords case sensitivity can be used in subsequent settting of the parameter SEC_CASE_SENSITIVE_LOGON to TRUE