Comprehensive Survey · 2026

Privacy Coins & Privacy-Preserving
Payment Systems

From Chaum's blind signatures to ZK rollups — a complete technical survey of cryptographic privacy in digital payments, 1982–2025.

32
Protocols / Papers
43
Years Span (1982–2025)
6
Tech Families
14
Crypto Primitives
5
Regulated CBDC Papers
Privacy Properties Comparison Matrix
Sender anonymity · Receiver anonymity · Amount hiding · Unlinkability · Auditability · Trusted setup requirement · Deployment chain
Protocol / Paper Family Year Sender Anon Receiver Anon Amount Hidden Unlinkable Auditable Trusted Setup Chain / Platform
Technology Family Deep Dive
Transaction flow and cryptographic steps for each major privacy technology lineage
Confidential Transactions — Transaction Flow
STEP 01
Pedersen Commit
C = rG + vH
→
STEP 02
Range Proof
Bulletproofs (no trusted setup)
→
STEP 03
Balance Verify
Σ inputs = Σ outputs (homomorphic)
Click a step to see cryptographic details
Key Properties
  • • Hiding: Pedersen commitment hides value — observer sees C, not v
  • • Binding: Computationally infeasible to open to two different values
  • • Homomorphic: C(v1) + C(v2) = C(v1+v2) — verifiable without revealing amounts
  • • Range Proof Evolution: Borromean ring sigs (large) → Bulletproofs (-80% size) → Bulletproofs++ (further optimization)
  • • Limitation: No sender/receiver anonymity unless combined with CoinJoin or stealth addresses
Protocols in this family
CT (Maxwell 2015)Confidential AssetsPriDe CTBulletproofsBulletproofs++Liquid NetworkPGC
RingCT — Triple Privacy Flow
STEP 01
Ring Signature
Hides sender in ring of decoys
→
STEP 02
Stealth Address
One-time receiver address
→
STEP 03
CT + Nullifier
Amount hidden, double-spend prevented
Click a step to see cryptographic details
Monero Evolution
  • • CryptoNote (2012): Ring sigs + stealth addresses. No amount hiding.
  • • RingCT 1.0 (2017): Added Confidential Transactions. Ring size 4→16.
  • • Bulletproofs (2018): Replaced Borromean ring sigs. Tx size -80%.
  • • CLSAG (2020): Concise Linkable Spontaneous Anonymous Group — 25% smaller signatures vs MLSAG.
  • • Bulletproofs+ (2022): Further range proof compression. Current default.
Zerocash/Zcash — zk-SNARK Shielded Flow
STEP 01
Note Commitment
COMM(addr, value, r) → Merkle tree
→
STEP 02
Spend Auth
ZK proof of note ownership
→
STEP 03
Nullifier Reveal
Prevents double-spend without revealing note
Click a step to see cryptographic details
Zcash Upgrade Path
  • • Sprout (2016): joinsplit, Groth16-era, trusted ceremony, 45KB→288B proofs
  • • Sapling (2018): BLS12-381, randomizable keys, 100× proving speedup
  • • Orchard/Halo2 (2021): Pasta curves, Plonkish, no trusted setup, recursive IVC
  • • MASP/Namada: Multi-asset extension — arbitrary tokens in one shielded pool
EVM Privacy — Shielded Pool Pattern
STEP 01
Deposit
Lock tokens, get leaf in Merkle tree
→
STEP 02
ZK Proof
Groth16/PLONK: know leaf, haven't spent
→
STEP 03
Withdraw
Submit proof + nullifier, receive at new address
Click a step to see cryptographic details
EVM Ecosystem Status
  • • Tornado Cash: OFAC sanctioned Aug 2022. Pertsev convicted 2024. Still running on-chain.
  • • RAILGUN: Compliant alternative. Full DeFi access (swap, lend) from shielded pool.
  • • Aztec Connect: ZK rollup, shut down July 2023 to rebuild as Aztec Network.
  • • Penumbra: Cosmos-native, IBC-compatible, private DEX with sealed-bid batch auctions.
Regulated CBDC Privacy — Threshold Architecture
STEP 01
ZK Transaction
Unlinkable payment, amount hidden
→
STEP 02
ZK Threshold Check
Prove spend ≤ limit without revealing amount
→
STEP 03
Regulator Trace
Threshold decryption reveals identity on court order
Click a step to see cryptographic details
Regulatory Privacy Balance
  • • Privacy guarantee: Individual transactions unlinkable to identity by default
  • • Compliance guarantee: ZKP enforces spending limits without revealing amounts
  • • Accountability: Threshold MPC decryption requires multi-party consent (judges/regulators)
  • • Key papers: Platypus (CCS 2022), PEReDi (CCS 2022), PARScoin (2023), DART (2025)
Historical Timeline
Key milestones from cryptographic privacy research to live deployments — hover for details
Protocol Cards
32 protocols and papers with full technical detail, crypto primitives, and lineage
Cryptographic Primitives Frequency
Which primitives appear most across all 32 protocols — a map of the cryptographic landscape
Open Research Challenges
Six hard problems at the frontier of privacy-preserving payments