Quiz: Self-Sovereign Identity

Question 1

The SSI trust triangle has three actors. Which set is correct?

(A) Prover, Challenger, Oracle
(B) Government, Blockchain, User
(C) Bank, Customer, Regulator
(D) Issuer, Holder (stores

Answer: (D) The SSI trust triangle separates roles: the Issuer (e.g., university) signs a credential, the Holder (e.g., Alice) stores it in a digital wallet, and the Verifier (e.g., employer) checks it using the Issuer's public key via a blockchain registry for DID resolution.

Question 2

A Verifiable Credential (VC) is a digitally signed statement. According to the lecture, what makes it "verifiable"?

(A) The issuer's private key signs the claim
(B) It is protected by a password that only the holder knows
(C) It is stored on a public blockchain where anyone can read it
(D) A government official stamps it with a physical seal

Answer: (A) VCs follow the W3C Verifiable Credentials Data Model 2.0 (Candidate Recommendation, 2024; final Recommendation expected 2025). The credential contains the issuer's DID, the subject's DID, the claim, the issuance date, and a cryptographic proof (e.g., Ed25519 or BBS+ signature). Tampering with any field breaks the signature. Source: W3C VC Data Model 2.0 (CR, April 2026).

Question 3

A DID (Decentralized Identifier) looks like did:web:example.com:alice. How does it differ from a traditional identifier like an email address?

(A) DIDs are always shorter than email addresses
(B) There is no meaningful difference -- both serve the same purpose
(C) DIDs require a monthly subscription fee
(D) Traditional identifiers are assigned and controlled by a central

Answer: (D) Google controls alice@gmail.com and can disable it. Alice controls did:key:z6Mkf... and no one can revoke it. DIDs resolve to a DID Document containing public keys. You can have many DIDs (one per relationship), unlike a single SSN. Over 150 DID methods are registered today, though the market has consolidated around did:web, did:key, did:jwk, and did:ebsi (EU). Source: W3C DID 1.0 Recommendation (July 2022); DID Spec Registries (April 2026).

Question 4

In the SSI model, the verifier never contacts the issuer directly. Why is this important?

(A) Because issuers charge a fee for every verification request
(B) Because contacting the issuer is too slow for real-time verification
(C) Because issuers are not connected to the internet
(D) Because if the verifier called the issuer

Answer: (D) The holder controls the entire verification flow. The verifier checks the cryptographic signature against the issuer's public key (obtained from the blockchain registry), but never contacts the issuer directly. There is no "phone home" that would reveal where you use your credential.

Question 5

In the "bouncer analogy," you show your passport to enter a bar. The bouncer sees your name, date of birth, address, nationality, photo, passport number, and expiry date. With SSI, what would you share instead?

(A) Your full passport data encrypted with the bar's public key
(B) A derived credential stating only "Over 18: TRUE
(C) A verbal confirmation of your age with no cryptographic proof
(D) A scanned copy of your passport uploaded to the bar's database

Answer: (B) This is "selective disclosure" -- reveal only the minimum attributes needed. The bouncer verifies the government's signature and confirms "over 18." No name, no birthday, no address. The lecture calls this the core idea of SSI: share only what is needed, nothing more.

Question 6

Tomoko, a Japanese student at ETH Zurich, verified her identity six times for six different organizations (Japanese bank, Swiss residence, Swiss bank, ETH, insurance, mobile). Each stores a copy of her data. What is the SSI solution?

(A) Tomoko verifies once with the government, receives VCs in her digital wallet
(B) Each organization shares Tomoko's data with the others through a data-sharing agreement
(C) Tomoko uploads her passport to a central EU database that all organizations can access
(D) Tomoko creates six different identities, one for each organization

Answer: (A) SSI shifts from "verify once per organization" to "verify once, present many times." Each of the six copies in Tomoko's current system is a breach target. With SSI, the verifier checks a cryptographic proof but does not need to store her underlying data.

Question 7

Diego, a Brazilian freelancer, completed 7 separate KYC processes this year, each taking 3-4 weeks. One platform rejected his ID because Brazil uses a different date format. What is the total cost of this identity fragmentation?

(A) Zero -- KYC processes are free for users
(B) $100 in platform fees
(C) 7 days of lost productivity
(D) 141+ days in personal time

Answer: (D) Diego's 7 KYC processes took 141+ days total. The system trusts none of its own previous checks. SSI would let Diego verify once and reuse credentials across platforms, reducing per-customer onboarding cost from $65-115 to $0.02-0.15 (a 99.8% reduction).

Question 8

The lecture presents four crisis numbers for identity. Which of the following is NOT one of them?

(A) Data breaches expose 300 million records annually
(B) KYC compliance costs $60 billion per year globally
(C) 5 billion people have been victims of identity
(D) 850 million people lack official ID

Answer: (C) The four numbers are: 850 million without ID (World Bank ID4D), $60 billion/year in compliance costs (Thomson Reuters), 300 million records breached annually, and 24-day average bank onboarding time. "5 billion identity theft victims" is not cited.

Question 9

eIDAS 2.0 (Regulation (EU) 2024/1183) entered into force in May 2024 and requires every EU member state to provide citizens with a European Digital Identity Wallet (EUDI Wallet) by late 2026. Which feature makes it different from existing government ID systems?

(A) It is voluntary for member states to implement
(B) It replaces physical passports entirely
(C) It supports selective disclosure and prevents issuers from
(D) It stores all citizen data on a single centralised EU server

Answer: (C) eIDAS 2.0 mandates selective disclosure, unobservability (issuers cannot track where credentials are used), cross-border acceptance, and mandatory recognition by banks, telecoms, large online platforms, and public services. It targets ~450 million users -- the largest SSI deployment in history. The EU Digital Identity Wallet (EUDIW) Architecture and Reference Framework (ARF) v1.5+ defines the technical spec, with member states required to issue wallets by November 2026. Source: Regulation (EU) 2024/1183; European Commission ARF (April 2026).

Question 10

The lecture compares traditional KYC costs ($65-115 per customer) with SSI-based KYC ($0.02-0.15). Where does the cost go in SSI -- is identity verification now free?

(A) The blockchain miners absorb the cost through transaction fees
(B) Yes -- SSI eliminates all identity verification costs completely
(C) No -- the issuer bears the one-time cost of creating
(D) The verifier pays the issuer a per-check fee

Answer: (C) The lecture is explicit: "SSI does not eliminate verification cost -- it shifts it to the issuance stage and amortizes it across many verifications." A university pays once to issue a diploma credential; hundreds of employers verify it at near-zero marginal cost.

Question 11

Government-led SSI rollouts in April 2026 include the EU (eIDAS 2.0 / EUDI Wallet), Switzerland (Swiss e-ID 2.0 / SwiyuID, adopted by Parliament in 2024 after the 2021 referendum rejected a private-consortium model), and India (Aadhaar). What is the main risk of the government-led approach?

(A) Government-led systems are always more expensive than crypto-native alternatives
(B) Governments may not resist the temptation to use the identity infrastructure
(C) Government-led systems cannot scale beyond a single country
(D) Government-led systems do not use cryptography

Answer: (B) The privacy-surveillance trade-off is the central tension in government-led digital identity. Switzerland is a revealing case: voters rejected the 2021 e-ID Act by 64.4% because credential issuance would have been outsourced to a private consortium (SwissSign). Parliament then adopted a state-issued, SSI-based design in 2024 (W3C VCs and DIDs, selective disclosure); the SwiyuID wallet beta is rolling out 2026-2027. SSI's cryptography prevents issuer tracking, but implementation details -- logging, backdoors, aggregated metadata -- can violate the promise. Source: Swiss Federal Office of Justice (April 2026).

Question 12

The lecture lists six DID methods (did:web, did:key, did:ion, did:ethr, did:cheqd, did:sov). What is the trade-off between blockchain-anchored DIDs (did:ion on Bitcoin) and web-based DIDs (did:web)?

(A) Web DIDs are more censorship-resistant than blockchain DIDs
(B) Blockchain DIDs are free; web DIDs cost money
(C) Blockchain-anchored DIDs are censorship-resistant but cost
(D) There is no trade-off -- both are identical in functionality

Answer: (C) did:ion anchors to Bitcoin and is censorship-resistant but Microsoft wound down its hosted ION node in 2024 and the method is now community-maintained. did:web uses DNS (free, fast) but depends on web servers that can go offline. Caveat: several early blockchain-anchored methods have eroded -- the Sovrin Foundation collapsed financially in 2022-2023 (did:sov usage migrated to did:indy or was abandoned); uPort/Serto pivoted away from SSI in 2022; Microsoft Entra Verified ID has seen low enterprise traction. The market in 2026 is converging on did:web, did:key, did:jwk, and did:ebsi (EU). Source: W3C DID Spec Registries (April 2026); Sovrin Foundation wind-down notices (2022-23).

Question 13

In the Zero-Knowledge Proof (ZKP) age verification example, your wallet computes a proof that your date of birth is before a certain date. What does the verifier learn?

(A) Your full date of birth, but not your name
(B) Only "over 18: TRUE"
(C) Your name and age, but not your address
(D) Nothing -- the verifier cannot determine your age

Answer: (B) The wallet takes the credential (DOB = 15/03/2003) and today's date, computes a statement "DOB is before 01/04/2008" (age >= 18), and produces a cryptographic proof of a few hundred bytes. The verifier checks the proof against the government's public key. Result: "over 18 = TRUE." Nothing else.

Question 14

The "color-blind friend" analogy explains ZKP intuition. Your friend holds two balls (red and green) and thinks they are identical. You want to prove they are different without revealing which is which. After 20 rounds of correct guesses, what is the probability you were just lucky?

(A) Approximately 0.0001%
(B) 0% -- certainty is guaranteed after 2 rounds
(C) 10%
(D) 50%

Answer: (A) Each round has a 50% chance of guessing correctly. After 20 rounds, the probability = (1/2)^20 = approximately 0.0001%. The friend is convinced the balls are different, yet still does not know which is red. In SSI, cryptographic ZKPs (BBS+ signatures, zk-SNARKs) achieve this without interactive rounds.

Question 15

Amira is a 28-year-old Syrian refugee in Germany with no documents. She has a computer science degree but no proof. She cannot open a bank account, rent an apartment, or get a SIM card. The lecture calls this a "circular dependency." What does that mean?

(A) To get identity documents, you need identity documents
(B) The German government is running a circular economy pilot program
(C) Amira can solve the problem by visiting government offices in a circular route
(D) Amira needs to apply for documents in a specific circular order

Answer: (A) An estimated ~850 million people lack any officially recognised ID (World Bank ID4D initiative). SSI aims to break the circular dependency by letting credentials be issued by any trusted party (NGO, employer, community leader) and verified without requiring a prior government-issued document. The 2024 Global Findex (published 2025) separately shows ~1.0-1.2 billion adults remain unbanked, with lack of ID a top barrier. Source: World Bank ID4D Global Dataset; Global Findex 2024.

Question 16

SSI stores credentials in a digital wallet on your smartphone. What is the key management challenge this creates?

(A) Smartphones are too slow to perform cryptographic operations
(B) ISPs can intercept wallet data during credential presentations
(C) Digital wallets cannot store more than 3 credentials at a time
(D) If you lose your phone or your private key is compromised

Answer: (D) Key management is SSI's biggest usability challenge. Self-sovereignty means self-responsibility. Solutions include social recovery (trusted contacts can help restore), cloud backup (but introduces a centralised dependency), and hardware security modules (but adds cost).

Question 17

The lecture states that 300 million records are exposed in data breaches annually. How does SSI reduce this attack surface?

(A) SSI encrypts all data with quantum-resistant algorithms
(B) SSI requires verifiers to delete all data within 24 hours
(C) Verifiers check cryptographic proofs but do not need to store copies
(D) SSI stores all personal data on the blockchain where it cannot be hacked

Answer: (C) In Tomoko's current system, 6 organizations each store a full copy of her data -- each is a breach target. With SSI and selective disclosure, the bar knows "over 18: TRUE" but not her name or birthday. Counter-example: centralised national-ID schemes concentrate risk. Estonia's ROCA incident in 2017 forced the suspension or re-issuance of ~760,000 national ID cards at tens of millions of euros in direct cost, because a shared cryptographic library vulnerability (CVE-2017-15361) affected every card. Biometric-central approaches raise a different concern: Worldcoin (iris-scanning "World ID") has faced bans or investigations in Kenya (2023), Germany (BfDI), Spain, Hong Kong, and Portugal for GDPR and data-minimisation concerns. Source: Estonian e-Governance Academy post-incident report (2017-18); BfDI rulings on Worldcoin (2023-24).

Question 18

The lecture identifies three layers of identity: who you are (biometrics), what others say about you (credentials), and how you prove it (documents/tokens). SSI primarily addresses which layer?

(A) Layer 1 -- SSI changes who you fundamentally are
(B) Layer 3 -- SSI gives you control over how you
(C) Layer 2 -- SSI changes what others say about you
(D) All three layers equally

Answer: (B) The lecture makes this explicit: "today, layer 3 is controlled by others -- governments issue passports, banks verify addresses, universities grant diplomas. You carry the credentials but never truly own them." SSI aims to give you control over layer 3.

Question 19

A university issues a VC stating "Alice holds a BSc in Finance from the University of Zurich." Ten years later, the university shuts down. What happens to Alice's credential?

(A) The cryptographic signature remains valid
(B) Alice must apply to another university for a replacement credential
(C) The blockchain automatically transfers the credential to another issuer
(D) The credential automatically expires when the university closes

Answer: (A) The lecture raises this as a "bonus question" in the think-pair-share exercise. The credential's signature is mathematically valid forever, but real-world trust requires knowing the credential has not been revoked. If the issuer disappears, the revocation registry becomes unmaintained.

Question 20

A government deploys SSI for national identity but adds a secret backdoor that logs every credential presentation. A citizen argues: "This is not self-sovereign identity -- it is state surveillance." Using the lecture's framework, evaluate this claim.

(A) The citizen is wrong -- all government identity systems require tracking for security
(B) The citizen is right
(C) The citizen is wrong -- SSI by definition cannot be surveilled
(D) The claim is irrelevant because no government would implement SSI

Answer: (B) The lecture's eIDAS 2.0 analysis explicitly asks: "Will governments resist the 'no tracking' requirement?" SSI is a design framework with specific privacy guarantees. Implementation can violate those guarantees. The lecture treats this as the central ethical question in digital identity.