How to extend the expiry for a GPG key pair and retrieve passphrase

How to extend the expiry for a GPG key pair and retrieve passphrase

AuthorFullName__c: Paul Pan
articleNumber: 000005125
ft:sourceType: Salesforce
FirstPublishedDate: 2021-10-14T22:38:37Z
lastModifiedDate: 2021-10-14
VersionNumber: 4

Affected Versions: 6.x and 7.x