Decentralized Identity Authentication and Access Control in Distributed Systems

Decentralized Identity Authentication and Access Control in Distributed Systems

Topic Description
In distributed systems, how can decentralized identity authentication and access control be implemented? The requirement is that users only need to log in once to securely access multiple independent services, and the system must avoid single points of failure or reliance on centralized permission servers.

1. Problem Background and Core Challenges
Traditional centralized identity authentication (such as Single Sign-On, SSO) relies on a central authentication server, which can become a performance bottleneck or a single point of failure. Distributed systems require decentralized solutions, with core challenges including:

  • Unified Identity Management: How is user identity information securely stored and verified?
  • Cross-Service Trust: How do services trust each other's user identities?
  • Dynamic Access Control: How to implement fine-grained and scalable permission management?

2. Core Idea: Token-Based Authentication and Public Key Infrastructure (PKI)
Decentralized identity authentication typically uses tokens (e.g., JWT) combined with asymmetric encryption technology:

  • Identity Token: After logging in, the user obtains an encrypted token containing identity information and presents it when accessing other services.
  • Decentralized Verification: Services confirm the user's identity by verifying the token's signature (instead of querying a central server). The signature is generated by the authentication service using a private key, and other services verify it with the corresponding public key.

3. Detailed Explanation of Key Technical Components

3.1 JSON Web Token (JWT) Structure
A JWT consists of three parts (separated by dots):

  • Header: Specifies the signature algorithm (e.g., RS256).
  • Payload: Contains user identity information (e.g., user ID, role) and token expiration time.
  • Signature: Signs the first two parts to prevent tampering.
    Example:
Header: {"alg": "RS256", "typ": "JWT"}  
Payload: {"sub": "user123", "role": "admin", "exp": 1672531200}  
Signature: RSA-SHA256(base64(Header) + "." + base64(Payload), privateKey)

3.2 Asymmetric Encryption Verification Process

  1. The authentication service generates a key pair (private key for signing, public key distributed to all services).
  2. After user login, the authentication service issues a JWT signed with the private key.
  3. The user accesses Service A with the JWT. Service A verifies the signature's validity and expiration using the public key.
  4. Service A performs permission checks based on the role information in the JWT.

3.3 Public Key Distribution and Rotation

  • Public Key Distribution: Distribute public keys to services via pre-configuration or dynamic discovery (e.g., OIDC Discovery endpoint).
  • Key Rotation: Regularly update key pairs. Old public keys must be retained until all issued JWTs expire.

4. Implementation of Decentralized Access Control

4.1 Claim-Based Permission Model
The JWT Payload can include permission claims (e.g., permissions: ["read:file", "write:db"]). Services directly parse the token and validate permissions without querying a central permission database.

4.2 Challenges of Dynamic Permission Updates
If a user's permissions change, already-issued JWTs remain valid until they expire. Solutions:

  • Short-Lived Tokens: Set short expiration times (e.g., 15 minutes) and use refresh tokens to obtain updated permissions.
  • Real-Time Permission Queries: After verifying the JWT, services additionally query a permission service (requires balancing the degree of decentralization).

5. Complete Process Example

  1. Login: The user submits credentials to the authentication service. After verification, the authentication service issues a JWT (containing user role and expiration).
  2. Access Service A:
    • The user includes the JWT in the request.
    • Service A retrieves the public key locally and verifies the JWT signature and expiration.
    • Service A parses the role from the JWT and allows or denies access.
  3. Access Service B: The process is the same as for Service A, requiring no re-login.

6. Advanced Optimization and Related Technologies

  • OAuth 2.0 and OIDC: Standardized protocols providing specifications for authorization and identity information exchange.
  • Blockchain Identity Authentication: Stores identity information on the blockchain for fully decentralized solutions (e.g., DID).
  • Zero Trust Architecture: Verifies identity for every access, dynamically adjusting permissions based on device and network context.

7. Summary
Decentralized identity authentication, through JWT and asymmetric encryption, distributes the responsibility of identity verification to individual services, avoiding single points of failure. The trade-offs include the need to address key management, token revocation, and dynamic permission updates. Real-world systems often combine standard protocols like OIDC to balance security and flexibility.