JWT With RSA256 Encryption ABAP Stack

FI3 — Tue, 02 Apr 2024 12:31:30 GMT

Hello.

I'm trying to create a JWT like on the website https://jwt.io/.

The signature section uses the SHA256withRSA / RSA256 algorithm with the private key provided.

How to make SHA256withRSA / RSA256 encryption with abap stack.

I have tried using Class cl_abap_hmac=>calculate_hmac_for_char and cl_abap_message_digest=>calculate_hash_for_char but it doesn't work.

Has anyone an idea how to achieve this?

Re: JWT With RSA256 Encryption ABAP Stack

caner_genis — Thu, 04 Apr 2024 07:27:21 GMT

Hello FI3,

Could you please check this code?

PRIVATE SECTION. TYPES: BEGIN OF ty_jwt_header, alg TYPE string, typ TYPE string, END OF ty_jwt_header . TYPES: BEGIN OF ty_jwt_payload, secret TYPE string, " private key iat TYPE i, "Issued At exp TYPE i, "Expiration Time END OF ty_jwt_payload .

METHOD generate_jwttoken. TRY. DATA(ls_header) = VALUE ty_jwt_header( alg = me->t_params[ name = c_alg ]-value "HS256 typ = me->t_params[ name = c_typ ]-value ). "JWT DATA(lv_json_header) = /ui2/cl_json=>serialize( data = ls_header compress = abap_on pretty_name = /ui2/cl_json=>pretty_mode-low_case ). DATA(lv_b64_header) = cl_http_utility=>if_http_utility~encode_base64( lv_json_header ). DATA(lv_currentts) = zcl_bc_util=>generate_timestamp( iv_tzone = 'TURKEY' ). DATA(lv_plus5min) = lv_currentts + 300. DATA(ls_payload) = VALUE ty_jwt_payload( secret = me->t_params[ name = c_private ]-value iat = lv_currentts exp = lv_plus5min ). DATA(lv_json_payload) = /ui2/cl_json=>serialize( data = ls_payload compress = abap_on pretty_name = /ui2/cl_json=>pretty_mode-low_case ). DATA(lv_b64_payload) = cl_http_utility=>if_http_utility~encode_base64( lv_json_payload ). DATA(lv_xpublic) = zcl_bc_util=>conv_string_to_xstring( CONV string( me->t_params[ name = c_public ]-value ) ). DATA(lv_data) = lv_b64_header && '.' && lv_b64_payload. cl_abap_hmac=>calculate_hmac_for_char( EXPORTING if_algorithm = CONV string( me->t_params[ name = c_algorithm ]-value ) "SHA256 if_key = lv_xpublic if_data = lv_data IMPORTING ef_hmacb64string = DATA(lv_b64_hmac) ). DATA(lv_off) = strlen( lv_b64_hmac ) - 1. lv_b64_hmac = lv_b64_hmac(lv_off). REPLACE ALL OCCURRENCES OF: '/' IN lv_b64_hmac WITH '_', '+' IN lv_b64_hmac WITH '-'. me->v_token = lv_data && '.' && lv_b64_hmac. CATCH cx_abap_message_digest INTO DATA(lx_hmac). " Exception Class for Message Digest RAISE EXCEPTION TYPE zcx_kw EXPORTING textid = lx_hmac->if_t100_message~t100key. * CATCH zcx_bc_util INTO DATA(lx_bc). " * RAISE EXCEPTION TYPE zcx_kw * EXPORTING * textid = lx_bc->if_t100_message~t100key. ENDTRY. ENDMETHOD.

METHOD generate_timestamp. * IMPORTING !iv_tzone TYPE tznzone DEFAULT 'UTC' * RETURNING VALUE(rv_secs) TYPE tzntstmpl * RAISING zcx_bc_util. DATA ts1 TYPE c LENGTH 20. GET TIME STAMP FIELD DATA(ts). CONVERT TIME STAMP ts TIME ZONE iv_tzone INTO DATE DATA(dt) TIME DATA(tm). ts1 = dt && tm. DATA(ts2) = CONV tzntstmpl( '19700101000000' ). TRY. " Time Interval in Seconds rv_secs = CONV int4( cl_abap_tstmp=>subtract( EXPORTING tstmp1 = CONV tzntstmpl( ts1 ) tstmp2 = ts2 ) ). CATCH cx_parameter_invalid_range INTO DATA(lx_range). " Parameter with invalid value range "DATA(ls_t100) = set_message_from_obj( lx_range ). CATCH cx_parameter_invalid_type INTO DATA(lx_type). " Parameter with Invalid Type "ls_t100 = set_message_from_obj( lx_type ). ENDTRY. CHECK ls_t100 IS NOT INITIAL. * RAISE EXCEPTION TYPE zcx_bc_util * EXPORTING * textid = ls_t100. ENDMETHOD.

METHOD conv_string_to_xstring. DATA: ls_t100 TYPE scx_t100key. CALL FUNCTION 'SCMS_STRING_TO_XSTRING' EXPORTING text = iv_str mimetype = 'charset=utf-8' encoding = '4110' IMPORTING buffer = rv_xstr EXCEPTIONS failed = 1 OTHERS = 2. CHECK sy-subrc <> 0. * ls_t100 = set_messagge_from_sy( ). * RAISE EXCEPTION TYPE zcx_bc_util * EXPORTING * textid = ls_t100. ENDMETHOD.

Good luck.

Caner.

Re: JWT With RSA256 Encryption ABAP Stack

FI3 — Thu, 04 Apr 2024 09:34:36 GMT

Hello Caner.

Thankyou for the code. really appreciate it.

But for the requierement, i need to encrypt the signature with RS256 Algorithm instead of SHA256.

if we try at jwt.io we can choose RS256 in the dropdown list.

the output will be different beetween RS256 and SHA256.

i tried with cl_abap_hmac=>calculate_hmac_for_char with exporting if_algoritm = 'RSA256' then error occured.

is the RS256 algorithm not supported in SAP ?

Regrads.
FI3

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