Proof of Work Checkpoint

Reason about compact-target shifts, precision loss, header bytes, and inclusive nonce search.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. Using the course unsigned decoder, what target does 0x021234ab represent?

Select one answer.

0x1234 0x1234ab 0x1234ab00 0x12

2. What is the canonical compact encoding of the positive target 0x8000?

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0x02800000 0x03008000 0x02008000 0x03800000

3. Encode then decode target 0x123456ff. Why is the result 0x12345600?

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The hash function changed it Every target must be divisible by 256 The compact representation keeps only the leading mantissa precision The exponent is a signed byte

4. Bits=0x207fffff is serialized into which four header bytes?

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20 7f ff ff ff 7f ff 20 20 ff ff 7f ff ff 7f 20

5. Which input belongs in the second SHA-256 call of HashHeader?

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The first digest's 64-character hexadecimal text The original header followed by the first digest The first digest's 32 raw bytes Only the nonce bytes

6. Mine scans from zero through maxNonce=6 inclusive. All candidates fail. How many hashes of candidate headers are tested? Enter one decimal integer.

7. An implementation tests n<=maxNonce in a uint32 loop. What prevents a failed search from cycling at maxNonce=2^32-1?

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Stop after testing the endpoint, before incrementing Use < so the endpoint is never tested Reset n to zero on overflow and continue Change the target after every failure

8. A toy hash integer equals its decoded target. Which statement fits this exercise?

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Reject equality and claim full Bitcoin compatibility Accept equality; unsigned mantissa and big-endian raw digest are course-specific conventions Accept only if the nonce is zero Reject because the target must be prime

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