Crypto Foundations Checkpoint

Trace the representation, diagnose a boundary failure, and reconstruct a changed case.

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

1. An attacker flips ciphertext bits and the receiver acts on the altered plaintext without detecting it. Which missing guarantee is demonstrated? Select one.

Select one answer.

Availability during network partitions Forward secrecy after key deletion Protection against traffic volume analysis Integrity/authentication against modification

2. A uniform three-bit draw ranges from 0 to 7. Under r mod 3, how many draws map to residue 0?

3. To remove that three-bit modulo-3 bias, which accepted set gives equal residue counts? Select one.

Select one answer.

Accept all draws and hash the result once Accept 0 through 5 and retry 6 or 7 Accept 0 through 6 and retry 7 Reject only draw 0

4. Two ciphertext bytes reuse a pad: c1=0x12, c2=0x34. Known p1=0x56. Give p2 in hex.

5. A deterministic generator has uniform-looking outputs, but its state can be recovered from several outputs. Can it supply secret keys? Select one.

Select one answer.

Yes; uniform histograms prove cryptographic security No; statistical distribution does not establish prediction resistance Yes; determinism prevents attackers from guessing Only if keys are encoded in hexadecimal

6. Increasing ideal hash output from 64 to 80 bits multiplies generic collision work by approximately what power of two? Give the exponent.

7. Seed 1 produces XorShift output 0x47e4ce4b896cdd1d. Which state is saved for the next call? Select one.

Select one answer.

The multiplied output Zero The pre-multiplication XOR/shift value 0x2000001 The original seed 1

8. A birthday estimate exceeds maxInt. What does the exercise return? Select one.

Select one answer.

A wrapped negative int maxInt as an explicit saturation sentinel Zero, meaning collisions are impossible The low bits of the estimate

9. Two messages reuse a pad, but neither plaintext is known. What is directly recovered by XORing their ciphertexts? Select one.

Select one answer.

Both full plaintexts separately The secret pad alone Nothing at all The XOR relation between the two plaintexts

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