These are recommended plugins. If you find a better one let me know.
Drawing - Hands down it's Gliffy.
Prototyping - Balsamiq
Evaluating
Spreadsheet Functionality in Tables
Must work in mobile. Integrate with existing Confluence Table inline.
Spreadsheets for Confluence - not able to meet criteria.
Encryption
Looks promising, no public key, but simple enough - https://marketplace.atlassian.com/plugins/com.prcpo.confluence.plugins.secure-content-block
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