Re: FieldProc Error - column has returned invalid data on a Zoned Numeric column

Nathan

Field proc programs don't yet allow the use of any SQL. They also don't
yet support calling a program or command that directly or indirectly runs
SQL statements. Example: you can't call IBM's API to create a key store
file, from inside a field procedure program, because that API runs SQL in
its plumbing.

I've gotten all that encryption field procedure stuff to work well, but i
was a PITA getting it all to work. I utilized code from at least a handful
of sample programs.

- AES 256-bit encryption
- DEKs (data encryption keys) stored in key store files.
- Using KEKs (key encrypting keys) to encrypt the DEKs (data encryption
keys), also stored in key store files.
- Using master keys to encrypt the key store files.
- Using tokens with the encryption APIs so the keys can't be retrieved
even under debug.

If you're trying to take a zoned decimal number, encrypt it, and store it
in the database, you need to store the result in:

- A CHAR or VARCHAR column with the FOR BIT DATA attribute applied,
which uses CCSID 65535.
- A BINARY column
- A VARBINARY column
- A BLOB column
- Or the DDS file defined equivalent of one of the above.

The encrypted data is a binary string that requires one of those data types
to store the results. Encrypted data doesn't conform to the set of hex
values that are allowable for storage in a zoned or packed decimal column,

Get the IBM Redbook "IBM System i Security: Protecting i5/OS Data with
Encryption". In the July 2008 version of that book, see chapter 7
"Database Considerations", section 7.2, pages 78 and 79 in particular, talk
about storage requirements of the encrypted data.

Another great PDF book is "Protecting IBM i data with encryption" by Kent
Milligan and Beth Hagemeister (March 2014). Read pages 31 through 33 for
storage requirements.

When you apply the field procedure to a column (ALTER TABLE ALTER COLUMN),
it calls the field procedure to encrypt that column for ALL rows of the
table.
When you drop a field procedure from a column (ALTER TABLE ALTER COLUMN),
it calls the field procedure to decrypt that column for ALL rows of the
table.

I imagine a field procedure could be used for a non-encryption purpose,
although I've not tried that (no use case comes to mind at the moment).
Assuming that is allowed, a field procedure that returns zoned decimal data
for storage in a zoned decimal column is fine to do, but not with encrypted
data.

HTH,

Mike

On Mon, Mar 23, 2020 at 4:48 PM Vernon Hamberg <vhamberg@xxxxxxxxxxxxxxx>
wrote:

Nathan

Is the numeric column in question a key of the file? Are you using
native record-level access? If either, then RPG might give you problems.
I thought it was only with keyed columns, but maybe not.

You might try using SQL to process the file.

Vern

On 3/23/2020 3:26 PM, Nathan Hughes wrote:

First I want to apologize for my ignorance in RPGLE...we typically don't

use this programming language, but have to for FieldProc purposes. I've
researched this issue for a couple weeks now, and cannot find a resolution.
I'm currently trying to write a field procedure program. I have taken the
IBM RPGLE example (https://www.ibm.com/support/knowledg...yfpexample.htm<
https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_73/sqlp/rbafyfpexample.htm>),
and started to modify it to work for us.

Here is the table that was created for testing purposes:
********** Beginning of data *************************************
A R REC
A ECNUM 16S 0 COLHDG('NUMBER')
A ALIAS(EC_NUMBER)
A ECALPHA 32A COLHDG('ALPHA')
A ALIAS(EC_ALPHA)
************* End of data ****************************************
The program from the link above allows for several SQL types, clob,

varchar, char, blob, etc., but I needed to add zoned numeric. To begin, I
studied and stepped through the program to see what it was doing, and
thought I had a good understanding of how it worked. I then started adding
what appeared as necessary for the SQL_TYP_ZONED (488).

When I send the 'ALTER TABLE' command and set the FieldProc program on a

column, the first call is to Register(function code: 8), the next is
Encode(function code: 0) to encode the values in said column.

I set a breakpoint at the end of the program, and evaluated the

parameters when setting the FieldProc on a VARCHAR and ZONED NUMERIC
columns, and besides being different data types all appears correct, but
the ZONED NUMERIC column abruptly stops with the error below after the
register call.

Message ID . . . . . . : SQL0685
Date sent . . . . . . : 03/18/20 Time sent . . . . . . : 16:17:04

Message . . . . : Field procedure on column ECNUM has returned invalid

data.

Cause . . . . . : Field procedure on column ECNUM has returned invalid

data.

Recovery . . . : Change the field procedure to return valid data.

Thank you in advance for any help you can give on this.

Thanks,
Nathan Hughes
Software Developer

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