Zero-Knowledge Proofs for Enhanced Privacy

Registration Without a Phone Number on Signal

Signal Foundation

2024

02

The Privacy Challenge

Why phone number registration raises concerns

Current Registration Model

01

Phone Number Required Signal currently requires a valid phone number for account registration and verification
02

Metadata Exposure Phone numbers can reveal user identity, location, and enable contact discovery
03

User Privacy Concerns Privacy-focused users want alternatives that don't expose their phone numbers
04

Growing Demand 242 HN points reflect strong community interest in privacy-preserving solutions

Understanding Zero-Knowledge Proofs

A cryptographic breakthrough for privacy

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Prove Without Revealing

Demonstrate you know a secret without disclosing the secret itself

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Cryptographic Guarantee

Mathematical proof that verification is valid without exposing underlying data

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Trust Without Data

Verify identity and authorization without storing sensitive information

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Efficient Verification

Modern ZKPs enable fast, practical implementation at scale

05

ZKP-Based Registration

Signal's privacy-preserving approach

How ZKP Registration Works

1

Generate Key

User creates a cryptographic key pair locally on device

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2

Create Proof

Generate zero-knowledge proof of key ownership without revealing the key

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3

Submit Proof

Send proof to Signal servers for verification

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4

Verify & Register

Server validates proof and creates account without phone number

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5

Secure Access

User accesses Signal with enhanced privacy protection

Traditional vs ZKP Registration

Phone-Based

Requires valid phone number
Phone number stored in database
Metadata can be exposed
Linked to real-world identity

ZKP-Based More Private
No phone number required
No identifying data stored
Cryptographic privacy guarantee
Pseudonymous by design

Thank You

Zero-knowledge proofs mark a significant step forward for privacy in secure messaging

signal.org