We introduce Cryptis, an extension of the Iris separation logic for the symbolic model of cryptography. The
combination of separation logic and cryptographic reasoning allows us to prove the correctness of a protocol
and later reuse this result to verify larger systems that rely on the protocol. To make this integration possible,
we propose novel specifications for authentication protocols that allow agents in a network to agree on the use
of system resources. We evaluate our approach by verifying various authentication protocols and a key-value
store server that uses these authentication protocols to connect to clients. Our results are formalized in Rocq.