こゆのでいいんと思うんよね
$ echo zundaに2021年4月24日に2回目のファイザーを打ったよ | gpg --sign --armor
-----BEGIN PGP MESSAGE-----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=/mPi
-----END PGP MESSAGE-----
x509証明書で署名するのはコマンドライン違うだろうけど