I want to decrypt the password which is encrypted by oracle 10g.
The encrypted password like
'S:987DFSSDF9879SDFD80FSS0D8DFH8F0H77S;234SDFSF987FSDF34E'
You cannot decrypt it. It is not encrypted as such, it is a one-way hash.
You'll need to login as a privileged user and set the password for that user to something new.