liveBook · Manning

Identity key

As explained in Real-World Cryptography

An identity key is a long-term cryptographic key that represents a messaging user and supports authentication of that user's protocol participation.

An identity key is a long-term cryptographic key representing a messaging user. Signal uses it as one component of X3DH, alongside signed prekeys and one-time prekeys. section 10.4.2

A long-lived identity key helps identify a participant, but using identity keys alone would provide no forward secrecy: compromising the key could expose previous sessions. section 10.4.2

In the Signal handshake:

  • A user registers an identity key with a signed prekey and multiple one-time prekeys. section 10.4.2
  • X3DH combines several Diffie-Hellman exchanges, using the resulting key material in a later messaging protocol. section 10.4.2

How Real-World Cryptography covers it

How deep it goes
Defines the key’s purpose and limitation, then places it in registration and prekey-bundle retrieval without detailing cryptographic computation.
Examples
Uses Alice and Bob’s Signal conversation, where Alice retrieves Bob’s long-term key in a prekey bundle.
What it assumes
Assumes basic familiarity with cryptographic keys and introduces the identity, signed-prekey, and one-time-prekey roles together.
What you can do after
Evaluate how a long-term key participates in Signal’s handshake and why it cannot provide forward secrecy alone.
How it connects
Connects identity keys to forward secrecy, Diffie-Hellman key exchange, X3DH, signed prekeys, one-time prekeys, and prekey bundles.
Cover of Real-World Cryptography
liveBookmanning.com
Read Real-World Cryptography on liveBook Get the book at manning.com

Related concepts

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.