Grokking Bitcoin

Appendix B. Answers to exercises

Chapter 2

2.1

256 bits.

2.2

32 bytes.

2.3

A cryptographic hash function.

2.4

061a is 6*256 + (16 + 10) = 1,536 + 26 = 1,562 in decimal form. The binary form of 06 is 0000 0110, and the binary form of 1a is 0001 1010, so the full binary representation is 0000 0110 0001 1010.

2.5

No. If it was possible, the function wouldn’t be second-pre-image-resistant.

2.6

Properties 2 and 4 are lacking.

2.7

Second-pre-image resistance is stopping the attacker. The attacker needs to find an input that gives the same hash as a certain other input: the cat picture.

2.8

The money supply increase rate will decrease over time because the reward to Lisa halves every 4 years. This means ...