HMAC implementation

[Former Member]

I would like to ask, if somebody already implemented HMAC algorithm with ABAP.

(http://tools.ietf.org/html/rfc2104#section-3). I need to calculate the HMAC-SHA1 hash code for authentification purposes.

thanks,

martin

[Former Member]

My solution of HMAC implementation:

FUNCTION Z_CALCULATE_HMAC .
*"----------------------------------------------------------------------
*"*"Local Interface:
*"  IMPORTING
*"     REFERENCE(IV_HASH_ALG) TYPE  HASHALG 
*"     REFERENCE(IV_MESSAGE) TYPE  XSTRING
*"     REFERENCE(IV_KEY) TYPE  XSTRING
*"  EXPORTING
*"     REFERENCE(EV_HASH) TYPE  HASH160
*"----------------------------------------------------------------------

* H(K XOR opad, H(K XOR ipad, text))
* B = 64 bytes

  DATA: ipad_x TYPE xstring,
        opad_x TYPE xstring,
        key_x  TYPE xstring,
        x1     TYPE x,
        x2     TYPE x,
        x3     TYPE x,
        length_key     TYPE i,
        chars_appended TYPE i,
        xor1           TYPE xstring,
        xor2           TYPE xstring,
        ev_hash_x      TYPE hash160x.

* -- index 0. - ipad, opad
* ipad = the byte 0x36 repeated B times
* opad = the byte 0x5C repeated B times.
  x1 = '36'.
  x2 = '5C'.
  x3 = '00'.
  DO 64 TIMES.
    CONCATENATE ipad_x x1  INTO ipad_x IN BYTE MODE.
    CONCATENATE opad_x x2  INTO opad_x IN BYTE MODE.
  ENDDO.

* -- index 1. - extend key to 64 bytes
* append zeros to the end of K to create a B byte string
* (e.g., if K is of length 20 bytes and B=64, then K will be appended with 44 zero bytes 0x00)
* KEY is already sended in HEX format
  key_x = iv_key.
  length_key = XSTRLEN( key_x ).

  chars_appended = 64 - length_key.
  IF chars_appended > 0 .
    DO chars_appended TIMES.
      CONCATENATE  key_x x3 INTO key_x IN BYTE MODE.
    ENDDO.
  ENDIF.

* -- index 2. - first calculation = Key XOR ipad
* XOR (bitwise exclusive-OR) the B byte string computed in step (1) with ipad
  xor1 = key_x BIT-XOR ipad_x.

* -- index 3.
* append the stream of data 'text' to the B byte string resulting from step (2)
* message is sended already in HEX format
*  iv_message_x = iv_message.
  CONCATENATE xor1 iv_message INTO xor1 IN BYTE MODE.

* -- index 4.
* apply H to the stream generated in step (3)
  CALL FUNCTION 'CALCULATE_HASH_FOR_RAW'
    EXPORTING
      alg  = iv_hash_alg
      data = xor1
*      length = 20
    IMPORTING
      hashx = ev_hash_x.

* -- index 5.
* XOR (bitwise exclusive-OR) the B byte string computed in step (1) with opad
  xor2 = key_x BIT-XOR opad_x.

* -- index 6.
* append the H result from step (4) to the B byte string resulting from step (5)
*  iv_message_x = ev_hash_x.
  CONCATENATE xor2 ev_hash_x INTO xor2 IN BYTE MODE.

* -- index 7.
* apply H to the stream generated in step (6) and output the result
  CALL FUNCTION 'CALCULATE_HASH_FOR_RAW'
    EXPORTING
      alg  = iv_hash_alg
      data = xor2
    IMPORTING
      hash = ev_hash.

ENDFUNCTION.

Usage:

CALL FUNCTION 'Z_TFM_CALCULATE_HMAC'
  EXPORTING
    iv_hash_alg       = 'SHA1'
    iv_message        = '4D415254494E' "MARTIN
    iv_key            = '42524154'      "BRAT
 IMPORTING
   EV_HASH           = LV_HASH          .

regards,

martin

[Former Member]

Hi Martin,

I am trying to use your function module but it's not giving the result that the vendor is expecting. We have a similiar requirement of generating trusted key based on shared secret key and user id parameter. The sample trusted key 4c076e4be0de707193002f8ec723909c generated from shared key 'secret' and parameter 'user_IDJSMITH' is not the same that i m getting from ur FM. Can you please advice.

Regards...

Vinay

[Former Member]

I solved it already.

[WolfgangJanzen]

The ABAP function modules CALCULATE_HMAC_FOR_CHAR and CALCULATE_HMAC_FOR_RAW are part of the standard shipment (SAP_BASIS) as of NetWeaver 7.1 - it was also downported to NetWeaver 7.0 Enhancement Pack 1 (see [SAP Note 1133249|https://service.sap.com/sap/support/notes/1133249]). Downports to older releases are not planned.

Best regards,

Wolfgang