Slides presented at the International Conference on Enterprise Design, Operations, and Computing (EDOC) Conference, held in Groningen, The Netherlands, October 30 - November 3, 2023. Link to the paper: https://link.springer.com/chapter/10.1007/978-3-031-46587-1_4 Abstract: Multi-party business processes rely on the collaboration of various players in a decentralized setting. Blockchain technology can facilitate the automation of these processes, even in cases where trust among participants is limited. Transactions are stored in a ledger, a replica of which is retained by every node of the blockchain network. The operations saved thereby are thus publicly accessible. While this enhances transparency, reliability, and persistence, it hinders the utilization of public blockchains for process automation as it violates typical confidentiality requirements in corporate settings. In this paper, we propose MARTSIA: A Multi-Authority Approach to Transaction Systems for Interoperating Applications. MARTSIA enables precise control over process data at the level of message parts. Based on Multi-Authority Attribute-Based Encryption (MA-ABE), MARTSIA realizes a number of desirable properties, including confidentiality, transparency, and auditability. We implemented our approach in proof-of-concept prototypes, with which we conduct a case study in the area of supply chain management. Also, we show the integration of MARTSIA with a state-of-the-art blockchain-based process execution engine to secure the data flow.

1. MARTSIA: Enabling Data
Confidentiality for
Blockchain-based Process
Execution
Edoardo Marangone | marangone@di.uniroma1.it
Claudio Di Ciccio | diciccio@di.uniroma1.it
Daniele Friolo | friolo@di.uniroma1.it
Eugenio Nerio Nemmi | nemmi@di.uniroma1.it
Daniele Venturi | venturi@di.uniroma1.it
Ingo Weber | ingo.weber@tum.de

2. MARTSIA
2
Multi-Authority appRoach to Transaction System for Interoperating
Applications
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Process
Execution

3. Introduction
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• Blockchain technology
• Business processes between multiple parties
• Transparency: copy of the ledger, data freely accessible
• Security and privacy issues: hiding some data from the majority of users

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1. Guarantee data privacy among parties
2. Let parties exchange information in a secure way
3. Let parties hide data (or parts thereof) from other players
Objectives

5. Running example
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• Manufacturer
• National customs
• International customs
• International carrier
• International supplier
Actors

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Business Process Model and Notation (BPMN)
collaboration diagram

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Business Process Model and Notation (BPMN)
collaboration diagram

9. Approach
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10. MARTSIA approach
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Data owner
Data
Data
Reader
Reader
Data Data

11. Background
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Confidentiality
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• Blockchains (Ethereum Virtual Machine)
• Smart Contracts
• InterPlanetary File System (IPFS)
• Multi-Authority Attribute-Based Encryption (MA-ABE):
Ciphertext-Policy ABE (CP)
Ingredients

13. InterPlanetary File System (IPFS)
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 Distributed system for the storage and access to files
 No central authority
 Content-addressing to uniquely identify each file in the network
 Files scattered among several nodes (Merkle DAGs)
 Distributed Hash Table (DHT) at its core

14. and (Manufacturer@AUTH1 or (Supplier@AUTH2 and International@AUTH3)))
CP-MABE
14
• Multi-Authority Attribute-Based Encryption (MA-ABE): type of public-key encryption
• Ciphertext-Policy ABE (CP):
 Users are associated with attributes
 (propositional literals)
 Messages are associated with policies
 (propositional formulae on attributes)
• Attributes ex.:
43175279, Supplier, International, Manufacturer
• Policy ex.:
((43175279@AUTH1 and 43175279@AUTH2 and 43175279@AUTH3 and 43175279@AUTH4)
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Process
Execution

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Policy
Plaintext Ciphertext
Ciphertext Plaintext
Attributes Access key
1: ciphering
2: key generation
3: deciphering
0: pre-phase
Public and private keys
Public keys
Authority initialization
Private key
CP-MABE
Access key

16. MARTSIA approach
16
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Execution

17. MARTSIA approach
17
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Execution

18. MARTSIA approach
18
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Process
Execution

19. MARTSIA approach
19
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Process
Execution

20. MARTSIA approach
20
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Execution

21. 0: Initialization
21
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Confidentiality
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Process
Execution

22. Multi-party computation
22
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Enabling
Data
Confidentiality
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Execution
1. IPFS file with authorities’ metadata
Commit-then-open coin-tossing protocol
2. IPFS file with hashed pairing elements (Elliptic Curve Cryptography)
3. IPFS file with pairing elements in clear
4. IPFS file with public parameters
5. IPFS file with public key

23. 1: Key Management
23
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Process
Execution

24. 24
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Confidentiality
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Execution
1: Key Management

25. 25
Address: 0x123
Attributes: 43175279, Manufacturer
Address: 0x456
Attributes: 43175279, Supplier, International
Address: 0x789
Attributes: 43175279, Customs, National
Process instance ID: 43175279
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Data
Confidentiality
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Blockchain-
based
Process
Execution
1: Key Management

26. 1: Key Management
26
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Data
Confidentiality
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Blockchain-
based
Process
Execution

27. 1: Key Management
27
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Confidentiality
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Process
Execution

28. Authority key delivering
28
Authority
server
Client
Client – Server
SSL Connection
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Enabling
Data
Confidentiality
for
Blockchain-
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Process
Execution

29. Client
29
Key
request
Public
parameters
User
attributes
Private key
User secret key 1
Authority 1
Load elements
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Data
Confidentiality
for
Blockchain-
based
Process
Execution

30. Client
30
Key
request
Load
elements
User secret key 2
User secret key 3
User secret key 4
Authority 2
Authority 3
Authority 4
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Data
Confidentiality
for
Blockchain-
based
Process
Execution
Load
elements
Load
elements

31. Client
31
User secret key 2 User secret key 3 User secret key 4
User secret key 1
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Confidentiality
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Blockchain-
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Process
Execution

32. 2: Data exchange
32
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Data
Confidentiality
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Blockchain-
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Process
Execution

33. 2: Data exchange
33
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Data
Confidentiality
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Blockchain-
based
Process
Execution

34. Data owner
34
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Data
Confidentiality
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Process
Execution

35. Data owner
35
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Data
Confidentiality
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Blockchain-
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Process
Execution

36. Data owner
36
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Data
Confidentiality
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Process
Execution
Customs@A or
(43175279@2+ and (( Supplier@1+ and
International@1+) or
Manufacturer@1+ or
( Carrier@1+ and
International@1+)))
Customs@A or
(43175279@2+ and ( Supplier@1+ and
International@1+))
43175279@2+ and (( Supplier@2+ and
International@1+) or
Manufacturer@1+)
Customs@A or
(43175279@2+ and (( Supplier@1+ and
International@1+) or
Manufacturer@1+))
Data Policy Symmetric key
b’3:dhPS […] sG8=’
b’3:bj/5 […] E0I=’
b’3:KXHX […] MXQ=’
b’3:ewGV […] n5P=’

37. Data owner
37
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Data
Confidentiality
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Process
Execution

38. 2: Data exchange
38
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Data
Confidentiality
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Blockchain-
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Process
Execution

39. 2: Data exchange
39
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Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution

40. Reader
40
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MARTSIA:
Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution

41. Reader
41
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MARTSIA:
Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution

42. Reader
42
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MARTSIA:
Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution
b’3:dhPS […] sG8=’
b’3:bj/5 […] E0I=’
b’3:KXHX […] MXQ=’
b’3:ewGV […] n5P=’
Symmetric key

43. Reader
43
Symmetric key
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MARTSIA:
Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution
b’3:dhPS […] sG8=’
b’3:bj/5 […] E0I=’
b’3:KXHX […] MXQ=’
b’3:ewGV […] n5P=’

44. Reader
44
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Enabling
Data
Confidentiality
for
Blockchain-
based
Process
Execution

45. Focus
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Data
Confidentiality
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Execution
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43175279@1@2, International@3, Carrier@4
Why?
x4
Customs@A or
(43175279@2+ and
(International@1+ and
Supplier@1+))
Customs@A or (43175279@2+ and (International@1+ and Supplier@1+))

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Caterpillar interaction

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Gas expenditure and execution time

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Open challenges
• Implement APIs and a web interface to let users easily interact with
the system
• Perform data aggregation on the ciphered data using Trusted
Execution Environments (TEEs)
• Possibility to revoke access to data: InterPlanetary Name System
• Oracles that permit Smart Contracts to interact with off-chain data

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New features already available
• We decentralize the certification architecture for user accreditation
• We introduce majority-based mechanisms for system bootstrapping and updates to
increase robustness
• We conduct a formal analysis of security guarantees
• We integrate MARTSIA with available decentralized applications (DApp)
• We present a novel implementation on Algorand

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MARTSIA GitHub
MARTSIA EDOC paper
MARTSIA: Enabling Data Confidentiality for
Blockchain-based Process Execution
Edoardo Marangone, Claudio Di Ciccio, Daniele Friolo,
Eugenio Nerio Nemmi, Daniele Venturi, Ingo Weber
https://link.springer.com/chapter/10.1007/978-3-031-46587-1_4
https://github.com/apwbs/MARTSIA