CS251P - Lab 1 Questions
To complete the lab, please answer the questions below.
How long did your timed hashcash take to create mined2.txt, in seconds?
If you saw "1m27.683s" as the output of time, enter 87.683 as your answer.
For each additional bit of Proof Of Work (POW) security that you create, how much longer do you have to work on average?
A minute longer
Twice as long
Four times as long
Half as long
Ten minutes longer
Which of the following hash functions is the function Bitcoin uses for its POW block header hashing?
In Bitcoin, what cryptographic technology do you use to prove that you own bitcoins in order to spend them?
Cryptographic (digital) signatures
Proof Of Work (POW)
What does Bitcoin use Hashcash-style proof of work for?
Ensuring that only the users who previously received bitcoins can spend those bitcoins.
Securing the Bitcoin Core releases.
Encrypting peer-to-peer network communications in the Bitcoin protocol
Calculating a Bitcoin address from a public key
Making transaction validation compute- and capital-intensive enough to disincentivize manipulation
Given the above Poisson distribution regarding Bitcoin block generation, which of the following statements are true:
About 10% of blocks are expected to be generated within just 1 minute.
About 10% of blocks are expected to take longer than 22 minutes.
More than 50% of blocks are expected to be generated within 10 minutes.
Because the curve flattens near the top, some Bitcoin blocks may take significantly longer than 30 minutes to generated.
It’s expected that a new block will be generated within seconds of the previous block fairly often.
As of September 2015, new blocks on the Bitcoin block chain had 67 bits of proof of work. If creating a hash demonstrating 25 bits of proof of work security takes on average 77 seconds on a typical CPU without a hardware mining chip, how long would it take on average for it to generate a hash with 67 bits of security using a typical CPU? (Python is installed on the 21 Bitcoin Computer if you want to invoke its REPL to perform a calculation; otherwise, feel free to use a calculator installed on your laptop.)
600 seconds (10 minutes—the Hashcash/Bitcoin maximum)
248,351,037,212,708 seconds (about 7 million years)
43,401,138 seconds (about 502 days)
338,649,581,355,008 seconds (about 10 million years)
3,103,319,709 seconds (almost 100 years)
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