[dba-SQLServer] Encryption & SQL Server 2005

Dear List,
 
This ought to be simple:
 
I have 90000+ records in a table called CallerAccount.  There's also an
identity primary key, CallerAccountID, and a foreign key CallerID which
links to the rest of the information about our caller.  
 
Not surprisingly, I need to search for records in the table pertaining
to one account.  This may actually span several calls, and several
callers, and many days, so there may be several entries with the same
account number.  
 
If I were searching cleartext account numbers, this would be a piece of
cake:  Select * from CallerAccount where AccountNumber = '1234567890'.
 
Sadly, I am not searching cleartext account numbers.  AccountNumber is a
sensitive piece of data around here, so it is necessary that it be
encrypted, hence the table also contains a field EAccountNumber,
containing the binary encrypted value for AccountNumber.
 
I could decrypt all the account numbers in the table, write them to a
new field and search that.  But since 90000+ records is only the very
beginning of this table, it seemed like it OUGHT to be more sensible to
encrypt the one account number that I know, using the same certificate
and key that I have used on the whole table, then search for the
matching encrypted value.  To make this easy, I wrote the encrypted
value out to another table.  Then, I thought, I could arrive at the
records I am interested in with a join like this:

	SELECT        CallerAccount.CallerID,
CallerAccount.EAccountNumber
	FROM            CallerAccount INNER JOIN
	                         tempAccount ON
CallerAccount.EAccountNumber = tempAccount.tempEAccountNumber

Apparently however, the same data encrypted with the same certificate
and the same key does not actually turn out to the same binary value
twice.  It's taken me all afternoon to arrive, kicking and screaming, at
this conclusion, but I suppose it makes sense.  So I'm at a standstill,
back at decrypting all the records in the table before searching.
 
Do any of you have any advice, workarounds, wisdom or comfort for me?
 
Thanks, 
  
  
Liz 
  
  
Liz Doering 
elizabeth.j.doering at wellsfargo.com
<mailto:elizabeth.j.doering at wellsfargo.com> 
612.667.2447 
  
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