Re: Reg: Calculate HMAC without Key

[Peter Dow <petercdow@xxxxxxxxx>]

Hi Suren,

From what I've read about HMAC SHA1, a key is required.  If you do not 
provide a key, some implementations generate a random key for you.  If 
you want to be able to verify the hash, you'll need to save that key.

This is based on reading
https://stackoverflow.com/questions/27165107/check-hmac-sha1-without-key-in-c-sharp
and
https://stackoverflow.com/questions/25492833/what-key-is-used-by-openssl-command-for-hmac-if-key-is-not-passed-in-as-argume

In the latter, which is pretty old, it says that OpenSSL at that time, 
did not require a key, but that according to a guy on the OpenSSL 
mailing list, that was expected to change. The person answering the 
question actually showed the OpenSSL source code that handles the key.

--
*Peter Dow* /
Dow Software Services, Inc.
909 793-9050
petercdow@xxxxxxxxx
pdow@xxxxxxxxxxxxxx /

On 5/31/2024 4:45 PM, Suren K wrote:
> Hi All,
>
> I am trying to calculate HMAC for text data using (QC3CALHM,
> Qc3CalculateHMAC) API without a key using the SHA1 algorithm.
>
> When I Pass the blank Key I get the error as "CPF9DF5 The key context is
> not found or was previously destroyed."
>
> When I pass Null Key I get the error as "CPF9DF4 The key context token does
> not reference a valid key context."
>
> Is it possible to calculate HMAC without a key or is the key mandatory for
> calculating HMAC?
>
> Any help will be very much appreciated.
>
> Code I used for the reference
>
> /copy QSYSINC/QRPGLESRC,QC3CCI
>
> //‚API Error Datastructure
> dcl-ds ApiError qualified inz;
>      BytesProvided  int(10:0) inz(%size(ApiError));
>      BytesAvailable int(10:0);
>      MessageId      char(7);
>      Reserved       char(1);
>      MessageData    char(3000);
> end-ds;
>
> dcl-pr Pr_CalculateHMAC extpgm('QC3CALHM');
>      InputData   char(500) options(*varsize);
>      InputLength int(10) const;
>      Format      char(8) const;
>      AlgDsc      char(20) options(*varsize);
>      AlgFmt      char(8) const;
>      KeyDsc      char(20) options(*varsize);
>      KeyFmt      char(8) const;
>      Crypt       char(1) const;
>      Cryptdev    char(10) const;
>      HMAC        char(64) options(*varsize);
>      CalHashErrC likeds(ApiError) options(*nopass: *varsize);
> end-pr;
>
> //‚Prototype for EBCDIC to ASCII
> dcl-pr QDCXLATE extpgm('QDCXLATE');
>      len    packed(5:0) const;
>      data   char(32702) options(*varsize);
>      table  char(10) const;
> end-pr;
>
> data = 'abcd';
> //‚Convert the EBCDIC to ASCII
> len = %len(%trimr(data));
> QDCXLATE(len: data: 'QTCPASC');
> QC3HA = 2;
> KeyDsc = *allx'00';
>
> //‚Generate HMAC
> Pr_CalculateHMAC(data:%len(%trim(data)):'DATA0100':QC3D0500:
>                   'ALGD0500':KeyDsc:'KEYD0100':'0':' ':hmac:
>                   ApiError);
>
> Regards,
> Suren