1. Signing transactions anonymously with Identity Mixer in Hyperledger
Idemix team: Jan Camenisch, Manu Drijvers, Maria Dubovitskaya
Blockchain team: Elli Androulaki, Angelo De Caro, Andreas Kind, Alessandro Sorniotti
IBM Research - Zurich

2. (prove Over 17 from ID issued by eGov)
Identity Mixer
Attribute-based credentials
Strong authentication (signatures)
Privacy-preserving Access Control
Selective disclosure of attributes, predicates over attributes, full unlinkability
Auditability
Revocation
Preserving privacy and unlinkability
- Verification is done with the public key of the issuer only
Presentation Policy
(prove Over 17 from ID issued by eGov)

3. Identity Mixer vs. multiple X.509 TCerts
Certificate Authority (CA)
X.509
Identity Mixer
Attr 1
Attr 2
Attr 1
Attr 2
secret key
public key
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
Presentation
Policy 2
Presentation
Policy 1
trust
Attr 1
Attr 2
Attr 1
Attr 2
Presentation
Policy 1
Transaction B
Attr 1
Attr 2
Transaction A
Attr 1
Attr 2
Attr 1
Attr 2
Transaction A
Transaction C
Transaction B
Attr 1
Attr 2
Attr 1
Attr 2
Attr 1
Attr 2
CA’s public key
Verifier

4. Membership management with Identity Mixer
ECerts: (relatively) static enrollment certificates acquired via registration with an enrollment certificate authority (CA).
TCerts: Identity Mixer presentation proofs derived from ECert, without interaction with CA
Blockchain User B
Certificate Authority (CA)
Blockchain User A
TkeyB
shares public key U
Application
Membership
uses
uses
Ecert U
Requests
certificates
1xEcert
invokes SC txn
(signed with TkeyA,
encrypted with TkeyA, TkeyB…)
Application
(stored in wallet)
TkeyA
TkeyB
Accesses ledger
TkeyB … sc
deployed on every validating peer
Smart contract
Consensus Network
(signed with Ekey of origin,
encrypted with validators’ key)

5. Contribution Overview: MVP for Java SDK
User.java
(extend with GetSigningIdentity() method)
TransactionContext.java
Sign Transactions
Identity/SigningIdentity.java
IdemixSampleStore.java
Sign/Verify
(Generate/Verify
Presentation Tokens)
User Certificates
Idemixgen tool
KeyGen
Issuance
Revocation
Identity Mixer
crypto package
Generate CA keys
Issue ECert
Presentation
Verification
Audit