Mobi Protocol v21.0.0

A deterministic algorithm for deriving human-readable 21-digit identifiers from cryptographic public keys with uniform distribution (zero bias).

Overview

Mobi maps any secp256k1 public key to a unique 21-digit decimal number. Display 12 digits to users (like phone numbers). Store full 21 digits. Resolve collisions with extended forms.

Public Key: 17162c921dc4d2518f9a101db33695df1afb56ab82f5ff3e5da6eec3ca5cd917
     ↓
Full:    879-044-656-584-686-196-443  (21 digits, stored)
Display: 879-044-656-584              (12 digits, shown to users)

Why 21?

21 is Bitcoin's number. And 10²¹ = 1 sextillion possible values.

Digits	50% Collision At
12	1.4 million
15	44.7 million
18	1.4 billion
21	44.7 billion

Properties

• Deterministic: Same pubkey always produces same mobi
• Uniform: Rejection sampling ensures zero bias (every output equally likely)
• Hierarchical: Display (12) → Extended (15) → Long (18) → Full (21)
• Collision-resistant: Birthday collision at ~44.7 billion for full form
• Memorable: Phone number format, easy to read aloud
• Verifiable: Anyone can derive mobi from pubkey

Quick Start

C (Reference Implementation)

#include "mobi.h"

mobi_t m;
mobi_derive("17162c921dc4d2518f9a101db33695df1afb56ab82f5ff3e5da6eec3ca5cd917", &m);

printf("Display: %s\n", m.display);    // "879044656584"
printf("Full:    %s\n", m.full);       // "879044656584686196443"

char formatted[28];
mobi_format_display(&m, formatted);
printf("Formatted: %s\n", formatted);   // "879-044-656-584"

Rust

use megab::mobi::derive_from_hex;

let mobi = derive_from_hex("17162c921dc4d2518f9a101db33695df1afb56ab82f5ff3e5da6eec3ca5cd917").unwrap();
println!("Display: {}", mobi.display);           // "879044656584"
println!("Full:    {}", mobi.full);              // "879044656584686196443"
println!("Formatted: {}", mobi.display_formatted()); // "879-044-656-584"

Go

import "github.com/obiverse/beebase/crypto"

mobi, _ := crypto.DeriveMobiFromHex("17162c921dc4d2518f9a101db33695df1afb56ab82f5ff3e5da6eec3ca5cd917")
fmt.Println("Display:", mobi.Display)          // "879044656584"
fmt.Println("Full:", mobi.Full)                // "879044656584686196443"
fmt.Println("Formatted:", mobi.DisplayFormatted()) // "879-044-656-584"

Algorithm

FOR round = 0 TO 255:
  hash = SHA256(pubkey) if round == 0 else SHA256(pubkey || round)
  value = first 9 bytes as 72-bit big-endian integer
  IF value < 10^21:
    RETURN zero_pad(value, 21)

Rejection sampling ensures uniform distribution. Expected rounds: ~4.7.

See PROTOCOL.md for the complete specification.

Canonical Test Vectors

Input	Display	Full
0000...0000	587135537154	587135537154686717107
17162c...d917	879044656584	879044656584686196443

Implementations

Language	Location	Status
C	src/mobi.c	Reference (zero dependencies)
Rust	megab/src/mobi.rs	Production
Go	beebase/crypto/mobi.go	Production

Use Cases

• Lightning Addresses: 879044656584@beewallet.net
• Voice calls: "Send to 879-044-656-584"
• Identity routing: Route messages by mobinumber
• Collision resolution: Show 15/18/21 digits when needed

Build

make        # Build library
make test   # Run tests (22/22 pass)
make clean  # Clean build

License

MIT OR Apache-2.0

Copyright (c) 2024-2025 OBIVERSE LLC