Re: Encrypted Data to File -- MIDRANGE-L

Hi Carsten -

It's working! I must have been using a copy of the file that wasn't
VARLEN. So I've created a file with DDS fields that looks like this:

A FLDA 1024 CCSID(65534)
A VARLEN(32)
...

Is this an efficient way to hold the encrypted information? Are 32
byte fields long enough (I'm using TDES) to accommodate the following
unencrypted lengths - 9, 16, 20, 6? 24 doesn't seem to work.

My thought is to have a 'shadow' file that contains the encrypted
fields, and to blank out the corresponding fields in the 'master'
file. Another thought is to have one file with all encrypted fields,
regardless of 'master' file, with appropriate key information in the
encrypted file to pull out the associated fields. Any thoughts on
this?

I really appreciate the good code - thank you!

- Michael

On Thu, Apr 24, 2008 at 10:03 AM, Flensburg, Carsten
<Flensburg@xxxxxxxxxx> wrote:

Hi Michael,

Depending on the encryption algorithm and mode as well as the chosen
encryption block length, the 16 bytes credit card number might end up as
a 24 or 32 bytes cipher string. Given that you're using my service
program you're receiving a varying length cipher string value from the
encryption procedure, and if you assign that value directly to the file
VARLEN field and vice/versa to the decryption procedure, the correct
length actually should be preserved. Yet, as you point out, something
has to be different, because if you feed the cipher string directly back
everything works. Have you tried checking out the string lengths and
cipher strings in the debugger? If you want you can also send me your
code and I'll have a look.

Best regards,
Carsten

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Michael Ryan

Sent: 24. april 2008 15:30
To: Midrange Systems Technical Discussion

Subject: Re: Encrypted Data to File

Hi Carsten -

Thanks for the feedback. Your service program works quite well - thanks!

I'm trying this:

Encrypt:
Take a piece of encrypted data, say a 16 credit card number; Encrypt it
into a 1024 varying field; Store the 1024 byte varying field into a
physical file with the VARLEN field level keyword, or into an SQL table
as a VARCHAR;
Decryp:
Access the appropriate record in the database; Take the VARLEN or
VARCHAR field from the file/table; Decrypt into a 1024 varying field;
Extract the 16 bytes (known length based on the application).

Does this make sense?

Thanks!

On Thu, Apr 24, 2008 at 8:43 AM, Flensburg, Carsten
<Flensburg@xxxxxxxxxx> wrote:
> Hello Michael,
>
> You'd want to tag the physical file field with a CCSID(65535)
> keyword, to avoid possible conversion issues relating to treating the

> data as text - as opposed to the binary value a cipher string
represents.
>
> Judged by your description of the problem another more immediate
> concern would be how you preserve the actual length of the cipher
> string. You have to feed back the exact same string length to the
> decryption process as you received initially from the encryption
> process. So if you receive a cipher string with a length of 192
> bytes, store that value in a fixed field in your physical file having

> a length of f.x. 512 bytes, you'll need some way to ensury that
> you're only passing the actual 192 bytes cipher string back to the
> decryption process. Simply running a %Trim() against the file field
> is not a recommended method of obtaining the cipher string length, as

> there's a possibility that the encryption process returns the value
x'40' as the two rightmost nibbles.
>
> Best regards,
> Carsten
>
>
>
> -----Original Message-----
> From: midrange-l-bounces@xxxxxxxxxxxx
> [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Michael Ryan
> Sent: 24. april 2008 14:09
> To: Midrange Systems Technical Discussion
> Subject: Encrypted Data to File
>
> I've implemented Carsten Flensberg's service program to encrypt and
> decrypt data using the Cryptographic APIs. Works well. However, I'm
> having a problem writing to/reading from a physical file containing
> the encrypted data. I encrypt some data into a 1024A varying field,
> put the varying length field into a (smaller) fixed length field in
> the database, and then in a later process, read the encrypted data
> and attempt to decrypt it. I get a value back of blanks from the
> decryption, though I can see (in debug) that the encrypted data is
> there. If I don't move the encrypted data into the physical file
> field, I'm able to encrypt and decrypt. So it must be the physical
> file move that's causing the problem. Has anyone encountered this?
> What's the fix?
>
> Thanks!
> --
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