1.  Introduction

1.1 Bitcoin Mining

Bitcoin is a cryptocurrency. In the Bitcoin system Bitcoins are mined through proof-of-work mechanism. Bitcoin miners are given technical puzzles to solve. There is only one puzzle at any time with a given difficulty level, which is set by the system administrator. New puzzles are created after the current one is solved.

The first miner who solves the puzzle is awarded a specified number of bitcoins. The winner creates and sign a new block with digital signature technology and broadcast to other Bitcoin users. The signed block is linked to the previous signed blocks. These blocks form a chain of blocks (called blockchain) as shown in the following figure. The new signed blocks are verified by others and could become mature after being confirmed by a given number of miners, which is measured by length of blocks linked to the new blocks.

1.2 Technical puzzle

The puzzle set in the proof-of-work is to find a specific integer number (called nonce), which together with a few other numbers (such as hash value of the previous block, the transactions to be included to the new block)

are hashed with SHA-256 algorithm and the hashed value satisfies a given condition.

The puzzle can be formulated as follows:

where preHashis the hash value of the previous block, Tx is transaction of bitcoins. levelHard is a given number, usually controlled by requiring a consecutive number of most significant bits (MSB) being zeros, for example the first 30 MSBs being zero. The more MSB zeros required on levelHard, the more difficult to solve the puzzle (finding the nonce satisfying the condition). Below gives a binary number with the 15 MSB being zeros and 5 least significant bits (LSB).

(MSB) 00000000000000011100000101111110011010101100000 (LSB)

1.3 Signing and verifying a new block

The first miner solving the puzzle will create a new block, which includes a block header (storing the digital signature of this new block, which will include the hash value of the block body) and a block body. The block body includes the hash value of the previous block, the found nonce and transactions included in this block. The digital signature is created by encrypting the hash value of this new block with private key. The block is linked to the last block of the existing blockchain and broadcast. The new block will then be verified by others using the winning miner’s public key and checking the hash values of this and previous blocks.

2.  Specification

2.4 Task4: Verify the message authentication.  [4 marks]

o The message authentication is to be verified by decrypting the digital signature with public key {n,e} generated in Task 1 and comparing the hash value obtained from the decryption of the digital signature to that of the signed message.

o The process of verifying the message authentication needs to output yes or no depending on the verification outcome.

o Hint: you can utilize the Example 3 in the provided sample program to complete this task.

3.  Sample Program

We provide a sample python program miningBitcoin_sample.py, which includes most of the needed RSA encryption and digital signature functions to complete the above tasks. It can be run from integrated development environments (IDLE). It can also be run from the command line like this:

python mingingBitcoin_sample.py

You should modify the sample python program and add codes to complete the tasks, especially for Task2 on the proof-of-work part. A Google Colab notebook for the sample program is sharedhere.

Your own program should be called something like cs_bitcoin_registrationnumber.py (see naming instructions later). Your program must run from the command line like this:

python cs_bitcoin_registrationnumber.py

The outputs of your program are required to be displayed, following the specified format for marking purposes.

4.  How to submit

Submit one python .py file to Faser called:

cs_bitcoin_registrationnumber.py

For example, if your registration number is 1234567, your filename will be:

cs_bitcoin_1234567.py

Note that the filename is a .py file. The file name is all lower case.

5. Marking Scheme

You will be asked by the Dr He or teaching assistants at NWU to demonstrate your work and answer questions to ensure it is your own work. Your marks for this assignment will be dependent on the complement and output results of your program, and your answers to the questions asked by the teachers. If you are asked to but you don’t demonstrate your work, no mark will be given to your assignment work.

Apart from demonstration of your work to the teaching staff members, it is mandatory for you to submit your program file to Faser on time. Otherwise, you may not get any mark for your work on the assignment.

Your submitted program may be checked and tested by Dr He. If there are problems found from the testing, your marks received from your demonstration may be deducted.

Plagiarism

You should work individually on this project. Anything you submit is assumed to be entirely your own work. The usual Essex policy on plagiarism applies:http://www.essex.ac.uk/plagiarism/.