To secure iSCSI devices, require that the ESXi host, or initiator, can authenticate to the iSCSI device, or target, whenever the host attempts to access data on the target LUN.
Authentication ensures that the initiator has the right to access a target. You grant this right when you configure authentication on the iSCSI device.
ESXi does not support Secure Remote Protocol (SRP), or public-key authentication methods for iSCSI. You can use Kerberos only with NFS 4.1.
ESXi supports both CHAP and Mutual CHAP authentication. The vSphere Storage documentation explains how to select the best authentication method for your iSCSI device and how to set up CHAP.
Ensure uniqueness of CHAP secrets. Set up a different mutual authentication secret for each host. If possible, set up a different secret for each client that to the ESXi host. Unique secrets ensure that an attacker cannot create another arbitrary host and authenticate to the storage device even if one host is compromised. With a shared secret, compromise of one host might allow an attacker to authenticate to the storage device.