MeshCore Security and Encryption

MeshCore uses a layered cryptographic system verified from the project's source code. All claims on this page are sourced from src/Utils.cpp, src/MeshCore.h, and src/Identity.h in the official MeshCore repository.

Symmetric Encryption

• Algorithm: AES-128 (ECB mode with zero-padding for the final block)
• Key size: 16 bytes (CIPHER_KEY_SIZE = 16)
• The shared AES key is derived via ECDH (see below)

Message Authentication

• MAC: HMAC-SHA256 truncated to 2 bytes (CIPHER_MAC_SIZE = 2)
• Scheme: Encrypt-then-MAC - the ciphertext is MACed, not the plaintext
• Functions: encryptThenMAC / MACThenDecrypt

Key Exchange

• ECDH via X25519 - Ed25519 identity keys are transposed to X25519 for Diffie-Hellman key exchange (calcSharedSecret in Identity.h)
• The resulting shared secret is used as the AES-128 key for the session

Identity and Signing

• Identity keys: Ed25519
• Public key size: 32 bytes (PUB_KEY_SIZE = 32)
• Private key size: 64 bytes (PRV_KEY_SIZE = 64)
• Signature size: 64 bytes (SIGNATURE_SIZE = 64)
• Advertisements are signed with Ed25519 to prevent node identity spoofing

What This Means in Practice

• Messages between two MeshCore nodes use a unique AES-128 key derived from their ECDH exchange - no shared secret needs to be pre-distributed
• The MAC is only 16 bits (2 bytes). It reliably catches accidental corruption, but a deliberate attacker who can transmit can forge a packet that passes the MAC check with modest effort (expected ~32,000 attempts). Do not rely on MeshCore's MAC to prevent message forgery by a capable adversary — it is an integrity check, not strong authentication.
• Advertisements are Ed25519-signed, so an attacker cannot forge an advert for a public key they do not control. Note, however, that nodes are addressed by a short public-key prefix, so prefix collisions can cause addressing ambiguity (see the troubleshooting reference). Impersonation/confusion at the routing/addressing layer is possible; identity cannot be assumed unforgeable in an absolute sense.
• Channel/group messages use a shared symmetric key derived from the channel configuration. The channel key is shared by all members, so any member can forge messages attributed to any sender — channel "authentication" is group-level only. The default public channel uses a publicly known key (8b3387e9c5cdea6ac9e5edbaa115cd72), so public-channel traffic provides no confidentiality against anyone who knows that key. Do not treat public-channel traffic as private or secure against observers.

Source: Official MeshCore repository, src/Utils.cpp, src/MeshCore.h, src/Identity.h. Verified 2026-05-03.