Operations on Text File - Encrypt, Decrypt, Password Protected

Question

Dear Experts,
My requirement is to upload a text file  and do some operations on it and then encrypt the content in it ans save it on application server with password protected. Later i want to decrypt it.
Please help me for the following:
How to encyypt and decrypt the text file using standard encryption alogrithms like DES, MD5, RSA? Are there any standand function modules for both encryption and decryption which accepts a user defined public key?
How to download a password protected text file?
Thanks in advance.

Answer 1

CALL FUNCTION 'Z_CRYPT_FILE'
        EXPORTING
          SOURCE_PATH         = WS_PATH
          SOURCE_FILE         = WS_OLDFILE
          DESTINATION_PATH    = WS_NEW_PATH
          DESTINATION_FILE    = WS_NEWFILE
          SWITCH              = 'E'
          KEY                 = ZUSER_PW
          KEEP_SOURCE_FILE    = ' '
        EXCEPTIONS
          INVALID_SWITCH      = 1
          SOURCE_FILE_NOTFOUND = 2
          DIDNT_WORK          = 3.
FUNCTION MODULE Z_CRYPT_FILE 
DATA: CINPUT(300) TYPE C.
DATA: BEGIN OF LIST OCCURS 0,
        DATA(238) TYPE C,
        DELIMITER(04) TYPE C,
        FILE(12) TYPE C,
      END OF LIST.
DATA: SOURCE TYPE ZCHAR200.
DATA: DESTINATION TYPE ZCHAR200.
DATA: ZINDX TYPE I.
DATA: msg(100).
IF SWITCH = 'E'.
   IF FILETYPE = 'T'.
      OPEN DATASET SOURCE IN TEXT MODE FOR INPUT ENCODING DEFAULT
         message msg.
   ELSE.
      OPEN DATASET SOURCE IN BINARY MODE FOR INPUT message msg.
   ENDIF.
   IF SY-SUBRC <> 0.
      RAISE SOURCE_FILE_NOTFOUND.
   ENDIF.
   CLOSE DATASET SOURCE.
   CLEAR CINPUT.
   CONCATENATE '/usr/local/bin/gpg -sev -r'
    KEY
    '-o'
    DESTINATION
    SOURCE
   INTO CINPUT SEPARATED BY SPACE.
   CONCATENATE CINPUT '2>&1' INTO CINPUT SEPARATED BY ' '.
   CALL 'SYSTEM' ID 'COMMAND' FIELD CINPUT ID 'TAB' FIELD
                              LIST-SYS.
   IF FILETYPE = 'T'.  
      OPEN DATASET DESTINATION IN TEXT MODE FOR INPUT ENCODING DEFAULT
         message msg.
   ELSE.
      OPEN DATASET DESTINATION IN BINARY MODE FOR INPUT message msg.
   ENDIF.
   IF SY-SUBRC = 0.
      CLOSE DATASET DESTINATION.
      IF keep_source_file <> 'X'.
         CLEAR CINPUT.
         CONCATENATE 'rm' SOURCE INTO CINPUT
         SEPARATED BY SPACE.
         CALL 'SYSTEM' ID 'COMMAND' FIELD CINPUT ID 'TAB' FIELD
                        LIST-SYS.
      ENDIF.
   ELSE.
    write: 'Encryption error  on command: ',
       cinput.
    skip 1.
     loop at list.
        write: / LIST.
       endloop.
      RAISE DIDNT_WORK.
   ENDIF.
   IF FILETYPE = 'T'.  
      OPEN DATASET SOURCE IN TEXT MODE FOR INPUT ENCODING DEFAULT.
   ELSE.
      OPEN DATASET SOURCE IN BINARY MODE FOR INPUT.
   ENDIF.
   IF SY-SUBRC <> 0.
      RAISE SOURCE_FILE_NOTFOUND.
   ENDIF.
   CLOSE DATASET SOURCE.
   CLEAR CINPUT.
   CONCATENATE '/usr/local/bin/gpg -o'
    DESTINATION
    SOURCE
   INTO CINPUT SEPARATED BY SPACE.
   CONCATENATE CINPUT '2>&1' INTO CINPUT SEPARATED BY ' '.
   CALL 'SYSTEM' ID 'COMMAND' FIELD CINPUT ID 'TAB' FIELD
                              LIST-SYS.
  REFRESH LIST.
  CLEAR LIST.
   IF FILETYPE = 'T'. 
      OPEN DATASET DESTINATION IN TEXT MODE FOR INPUT ENCODING DEFAULT.
   ELSE.
      OPEN DATASET DESTINATION IN BINARY MODE FOR INPUT.
   ENDIF.
   IF SY-SUBRC = 0.
      CLOSE DATASET DESTINATION.
   ELSE.
*list output if error
      loop at list.
        write: / LIST.
       endloop.
      RAISE DIDNT_WORK.
   ENDIF.
ENDIF.