Table 1. Multiuser SSE—Key features comparison (✔: Supported; ✘: Not supported).

Ref.	Encryption	Storage utilisation	Searchability	Update
[3]	✘	Metadata on blockchain EHR on repository	✔	✘
[4]	✔	Encrypted index on blockchain EHR on cloud storage	✔	✘
[5]	✔	Entire EHR on blockchain	✔	✘
[6]	✔	Encrypted index on blockchain EHR on cloud storage	✔	✘
[7]	✘	Entire EHR on blockchain	✔	✘
[8]	✘	Entire EHR on blockchain	✔	✘
[9]	✘	EHR’s hashes on blockchain EHR on databases	✘	✔