Understanding KeepKey’s PIN Security System

Technical Overview

The KeepKey implements a sophisticated PIN entry system that protects against various attack vectors:

• Physical observation (shoulder surfing)
• USB-based keyloggers
• Screen content analysis
• Malware and spyware
• Brute force attempts

PIN Architecture

Your PIN can be 1-9 digits long, with each digit ranging from 0-9. This provides:

• Maximum combinations: 10^9 (1 billion) for 9-digit PINs
• Minimum recommended: 10^4 (10,000) for 4-digit PINs
• Three-attempt limit before device reset

The Cipher System

How It Works

The KeepKey employs a dynamic cipher system for PIN entry:

1. Randomized Matrix

   • 3x3 grid of numbers (0-9)
   • Positions scrambled on every connection
   • Numbers only visible on device screen

2. Dual Display Protection

Anti-Analysis Protection

The PIN display implements several security measures:

1. Pixel Balance Technology

   • Equal number of lit/unlit pixels per row
   • Prevents power analysis attacks
   • Defeats USB resistance monitoring

2. Visual Inversion

   • Numbers displayed twice with inversion
   • Maintains constant power consumption
   • Thwarts side-channel attacks

Security Implementation

Zero-Trust Model

The KeepKey operates under a zero-trust security model:

• Assumes host computer is compromised
• Requires on-screen verification for all actions
• Never exposes sensitive data to host

Critical Security Note: A hardware wallet without a screen cannot provide adequate security. The screen-to-processor connection is fundamental to the security model.

PIN Entry Process

1. Connection Phase

   • Device generates random cipher
   • Displays scrambled keypad
   • Awaits user input

2. Input Validation

   • Each digit processed independently
   • Position mapped through cipher
   • No direct number transmission

3. Confirmation Process

   • New cipher generated for confirmation
   • Prevents pattern analysis
   • Requires second entry match

Best Practices

PIN Selection

1. Length Considerations

   • Minimum: 4 digits
   • Recommended: 8 digits
   • Maximum: 9 digits

2. Avoid Common Patterns

   • Sequential numbers
   • Repeated digits
   • Birth dates
   • Phone numbers

Usage Guidelines

1. Physical Security

   • Shield screen during entry
   • Verify surroundings
   • Use in private when possible

2. Device Protection

   • Verify screen content matches expectations
   • Never enter PIN on unofficial interfaces
   • Keep track of attempt count

Recovery Preparation

1. Device Reset Protocol

   • Three wrong attempts trigger reset
   • All data wiped from device
   • Recovery phrase required for restoration

2. Backup Requirements

   • Keep recovery phrase secure
   • Document PIN securely
   • Plan for device loss/reset

Security Warning: Never share your PIN or recovery phrase with anyone, including KeepKey support staff. The cipher system ensures secure entry even on compromised computers, but only if you maintain PIN confidentiality.