how can i view source of encrypted stored procedure

to view a stored procedure's code you can use this statement

exec sp_helptext someSP

if you declare a stored procedure like this:

create proc pMySp
(
@testParameter nvarchar(50)
)
with encryption
as
select @testParameter



when you use 'exec sp_helptext pMySp' you will get a message that 'pMySp' is encrypted

no how can i view source of encrypted sp?