ABAP Meets #Blockchain

Yesterday I was reading about Blockchain, its architecture and other technical detail. I being from ABAP background thought of coding a basic blockchain in ABAP.  Please note that intent here is to build a basic blockchain so that its understanding can be increased. Implementation of the blockchain may differ based on the requirements but basic concept remains the same.

The other features such as power of distributed data management and sync, validation of blocks etc. is out of scope of this blog.

Blockchain Basics

As the name suggests Blockchain is basically chain or collection of blocks. Typically a block comprises of a header which has different fields, a hash (cryptic value) of previous block and Transactions Data in hashed form (we will dig into this in our next blog). The first block in the blockchain is known as genesis block. N number of transactions together make a block. These all block are distributed over the network as local copy on each connected node.

Once the maximum number of transactions in a block is reached, the three parts of the block which are header, data(detail of transactions) & previous block hash are  combined and hashed(encrypted ) with a key known as proof of work or nonce.  The correct key or proof of work is determined based on the difficulty level.  For example we say a generated hash is valid only and only if it contains 5 leading zero’s. So this leading 5 zero’s is known as the difficulty level.

The process of determining the right key consumes the major time and is known as mining. Depending on which currency it is, rewards are given accordingly to the one who finds a valid Proof of Work.  The moment someone finds a valid proof of work all the connected nodes are informed and if 50% of the nodes agreed then this new hash is added as a new block to the chain.

What we are planning to build

• A basic prototype of Blockchain, where a report will take input as difficulty level and number of blocks to be generated and then output will be hash and nonce for value for each hash. In the current blog our focus is to highlight how it works. In next blog we will focus on how the transactions are arranged in a block:)

ABAP Implementation of basic Blockchain

• Created a basic report with below mentioned selection screen parameter

PARAMETERS: diffle  TYPE char5,
            noblock TYPE i.

TYPES:BEGIN OF block,
        index     TYPE string,
        data      TYPE string,
        phash     TYPE string,
        timestamp TYPE string,
        chash     TYPE string,
        nonce     TYPE string,
      END OF block,
      ttyblock TYPE STANDARD TABLE OF block.
DATA:blockdata TYPE ttyblock.

• A Type for basic blockchain structure

• Genesis block
  • First step is to add genesis block, we are using SHA1 algorithm for encryption.

  DATA:blockdataline LIKE LINE OF blockdata,
       timestamp     TYPE timestampl,
       combineddata  TYPE string,
       gethash       TYPE REF TO cl_abap_message_digest.
  blockdataline-index = 0.
  blockdataline-data = 'My first Genesis block'.
  blockdataline-phash = '000000'.
  GET TIME STAMP FIELD timestamp.
  blockdataline-timestamp = timestamp.
  blockdataline-nonce  = 0.
  CONCATENATE blockdataline-index blockdataline-data blockdataline-phash blockdataline-timestamp blockdataline-nonce INTO combineddata.
  CALL METHOD cl_abap_message_digest=>calculate_hash_for_char
    EXPORTING
      if_algorithm  = 'SHA1'
      if_data       = combineddata
    IMPORTING
      ef_hashstring = blockdataline-chash.
  APPEND blockdataline TO blockdata.

• Determine Next Block Hash
  • An iterative loop to repeat number of blocked needed – 1 since genesis block is already added.
  • Inside block loop have another loop to concatenate current and previous hash data along with Nonce value and generate a hash. Validate the hash as per difficulty if valid exit and append the block

DATA:blockdataline LIKE LINE OF blockdata,
       prevblockdata LIKE LINE OF blockdata,
       nonce         TYPE i VALUE 1,
       noncestring   TYPE string,
       timestamp     TYPE timestampl,
       combineddata  TYPE string,
       flag          TYPE c,
       difflength    TYPE i.
  noblock = noblock - 1.
  difflength = strlen( diffle ).
**  // Do block-1 times as genesis block added previously
  DO noblock TIMES.
    blockdataline-index = sy-tabix.
    CONCATENATE 'Current Block ' blockdataline-index INTO blockdataline-data SEPARATED BY '-'.
    READ TABLE blockdata INTO prevblockdata INDEX blockdataline-index.
    IF sy-subrc EQ 0.
      blockdataline-phash = prevblockdata-chash.
    ENDIF.
    GET TIME STAMP FIELD timestamp.
    blockdataline-timestamp = timestamp.
*   Calculate valid hash
    WHILE flag EQ ''.
*     Nonce is the Proof of work
      noncestring = nonce.
      CONCATENATE blockdataline-index blockdataline-data blockdataline-phash blockdataline-timestamp noncestring INTO combineddata.
      CALL METHOD cl_abap_message_digest=>calculate_hash_for_char
        EXPORTING
          if_algorithm  = 'SHA1'
          if_data       = combineddata
        IMPORTING
          ef_hashstring = blockdataline-chash.
*     Valid hashfound
      IF blockdataline-chash(difflength) = diffle.
        flag = 'X'.
        blockdataline-nonce  = nonce.
        APPEND blockdataline TO blockdata.
        nonce = 1.
        CLEAR:blockdataline.
      ENDIF.
      nonce = nonce + 1.
    ENDWHILE.
    CLEAR flag.
  ENDDO.

• Output Display

What is expected next?

• Deep dive into Block transactions arrangement – Merkel tree
• Implementing Blockchain using BOPF – This will be more like learning BOPF by implementing a blockchain using it
• Adding flavor of CDS to Blockchains with annotations:)
• Finally if time permits a HCP UI5 app to display and run this chain rather than traditional report

Feel free to provide your feedback,open to all ears:). Lets share and learn.