Hash the Transcript

Shared Secret Joins

Finished combines the transcript hash with the shared secret.

highlighted = computed this step

Finished also needs the shared secret

The transcript hash alone is not the Finished check. The DH shared secret joins it.

hash plus shared secret\text{hash plus shared secret}
Shared secret joinsToy TLS transcript rows are recomputed from DH and certificate pins.Shared secret joins - hash=43itemvaluecheckClientHello4pinnedServerHello9pinnedCertificate digest33root signatureServerKeyShare19DH publicClientKeyShare8DH publicTranscript hash43weighted mod 97Shared secret2DH recomputeClient Finished64toy checkServer Finished70toy check

The shared secret is recomputed

The same DH pins give shared secret 2.

shared=2\text{shared}=2
Shared secret joinsToy TLS transcript rows are recomputed from DH and certificate pins.Shared secret joins - hash=43itemvaluecheckClientHello4pinnedServerHello9pinnedCertificate digest33root signatureServerKeyShare19DH publicClientKeyShare8DH publicTranscript hash43weighted mod 97Shared secret2DH recomputeClient Finished64toy checkServer Finished70toy check

Hash and secret sit together

The next checks use transcript hash 43 with shared secret 2.

H=43s=2H=43\quad s=2
Shared secret joinsToy TLS transcript rows are recomputed from DH and certificate pins.Shared secret joins - hash=43itemvaluecheckClientHello4pinnedServerHello9pinnedCertificate digest33root signatureServerKeyShare19DH publicClientKeyShare8DH publicTranscript hash43weighted mod 97Shared secret2DH recomputeClient Finished64toy checkServer Finished70toy check

Summary

Finished begins from two recomputed facts: the transcript hash and the shared secret.

ready for Finished\text{ready for Finished}
Shared secret joinsToy TLS transcript rows are recomputed from DH and certificate pins.Shared secret joins - hash=43itemvaluecheckClientHello4pinnedServerHello9pinnedCertificate digest33root signatureServerKeyShare19DH publicClientKeyShare8DH publicTranscript hash43weighted mod 97Shared secret2DH recomputeClient Finished64toy checkServer Finished70toy check