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mukul975
58 lines
2.5 KiB
Markdown
58 lines
2.5 KiB
Markdown
---
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name: implementing-end-to-end-encryption-for-messaging
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description: End-to-end encryption (E2EE) ensures that only the communicating parties can read messages, with no intermediary (including the server) able to decrypt them. This skill implements a simplified version
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domain: cybersecurity
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subdomain: cryptography
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tags: [cryptography, encryption, e2e, messaging, signal-protocol]
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version: "1.0"
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author: mahipal
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license: MIT
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---
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# Implementing End-to-End Encryption for Messaging
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## Overview
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End-to-end encryption (E2EE) ensures that only the communicating parties can read messages, with no intermediary (including the server) able to decrypt them. This skill implements a simplified version of the Signal Protocol's Double Ratchet algorithm, using X25519 for key exchange, HKDF for key derivation, and AES-256-GCM for message encryption.
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## Objectives
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- Implement X25519 Diffie-Hellman key exchange for session establishment
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- Build the Double Ratchet key management algorithm
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- Encrypt and decrypt messages with per-message keys
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- Implement forward secrecy (compromise of current key does not reveal past messages)
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- Handle out-of-order message delivery
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- Implement key agreement using X3DH (Extended Triple Diffie-Hellman)
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## Key Concepts
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### Signal Protocol Components
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| Component | Purpose | Algorithm |
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|-----------|---------|-----------|
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| X3DH | Initial key agreement | X25519 |
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| Double Ratchet | Ongoing key management | X25519 + HKDF + AES-GCM |
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| Sending Chain | Per-message encryption keys | HMAC-SHA256 chain |
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| Receiving Chain | Per-message decryption keys | HMAC-SHA256 chain |
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| Root Chain | Derives new chain keys on DH ratchet | HKDF |
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### Forward Secrecy
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Each message uses a unique encryption key derived from a ratcheting chain. After a key is used, it is deleted, ensuring that compromise of the current state does not reveal previously sent/received messages.
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## Security Considerations
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- Delete message keys immediately after decryption
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- Implement message ordering and replay protection
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- Use authenticated encryption (AES-GCM) for all messages
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- Protect identity keys with device-level security
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- Verify identity keys out-of-band (safety numbers)
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## Validation Criteria
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- [ ] X25519 key exchange produces shared secret
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- [ ] Messages encrypt and decrypt correctly between two parties
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- [ ] Different messages produce different ciphertexts
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- [ ] Forward secrecy: old keys cannot decrypt new messages
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- [ ] Out-of-order messages can be decrypted
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- [ ] Tampered messages are rejected by authentication
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