MatterEx.Crypto.GroupKey (matter_ex v0.3.1)

Matter group key derivation.

Derives operational group keys, per-group encryption keys, and group session IDs from epoch keys per Matter Core Specification section 4.15.3.

Summary

Derive the encryption key for a specific group.

Derive the operational group key from an epoch key.

Derive the privacy key from an operational group key.

Derive the group session ID from an operational group key.

@spec encryption_key(binary(), non_neg_integer()) :: binary()

Derive the encryption key for a specific group.

GroupEncryptKey = HKDF(salt="", ikm=OperationalGroupKey, info="GroupMessaging" || GroupId_LE16, length=16)

@spec operational_key(binary()) :: binary()

Derive the operational group key from an epoch key.

OperationalGroupKey = HKDF(salt="", ikm=EpochKey, info="GroupKey v1.0", length=16)

@spec privacy_key(binary()) :: binary()

Derive the privacy key from an operational group key.

GroupPrivacyKey = HKDF(salt="", ikm=OperationalGroupKey, info="GroupPrivacy", length=16)

@spec session_id(binary()) :: non_neg_integer()

Derive the group session ID from an operational group key.

Lower 16 bits of HMAC-SHA256(OperationalGroupKey, "GroupSession").