Private key storing
Security just tells you to encrypt everything but won't tell you how to achieve that in your particular software stack. You ...
For further actions, you may consider blocking this person and/or reporting abuse
For private keys, there is a NIST standard that is really helpful:
nvlpubs.nist.gov/nistpubs/SpecialP...
For public keys, the certificate transparency initiative has been going for few years and all major browsers now support it:
certificate-transparency.org/what-...
Unsurprisingly it's a cryptographic ledger system of when certificates were issued :)