DBCA obfuscated passwords

 I'm trying to write a silent dbca script but i don't want to keep the passwords in the file. I saw the obfuscatedPasswords flag but i can't find any documentation on it.

I tried to reuse the obfuscated passwords from a previous installation but i got an error "Invalid obfuscated passwords"

I obtained the obfuscated password for database accounts using  SELECT name,password FROM SYS.USER$ WHERE password is not null; 

I obtained the obfuscated password for ASM accounts by looking at the password file.

Maybe i just can't find the right document to explain usage of the obfuscated passwords option.