SP3 - Blind and ring signatures

Why is the bill identifier (r_i) included in the message to sign?

• To prevent double spending.

• To identify the user.

• To identify the bank.

• To avoid the user gets a signed bill with incorrect (higher) amount.

Why are multiple bills (m_i) needed to create a single bill?

• To prevent double spending.

• To identify the user.

• To avoid information leakage.

• To avoid the user gets a signed bill with incorrect (higher) amount.

Why are the random values (k_i) used?

• To disguise (blind) the message.

• To prevent double spending.

• To sign the message.

• To ensure the amount in the bill is correct.

Upon receiving k_i (forall i except x), what does the bank check?

• The amount of all the open bills are correct.

• There is no double spending.

• The identifiers for the bills are correct.

• The k_i values are indeed random.

What is the probability of deceiving the bank? (i.e. getting a signed bill with higher amount)

• 1/n

• 1/2*m

• m/n

• (1/2)^m

A user spends the same bill twice and gets as challenges from the vendors [0, 1, 1, 0] and [1, 1, 0, 1]. Is her identity revealed?

• Yes

• No

What is the probability of Alice's identity NOT being revealed when double spending a bill with m = 5?

• (1/2)^5

• 1/5

• 1-1/5

• 1/2

Given a ring signature made with r users (|U| = r), what is the probability of identifing the actual signer?

• 1/r

• 1/s

• s*1/2

• (1/2)^r

Given a ring signature made with r users (|U| = r), how many times is f(x_i) computed?

• r-1

• r

• 1/r

• s

Why is a "ring" created when computing a ring signature?

• v=z

• f_i(x_i) = y_i

• k=h(m)

• E_k is nested