gpg2生成具有 (S)igning、(E)ncryption、(C)ertification 使用集中的一个或几个的密钥。然而，例如 Enigmail 创建了一个主键，也为 (A) 身份验证设置，然后 GnuPG 会显示该主键。如何使用 设置/修改它gpg2？我在 中找不到任何命令--edit-keys，当我创建子项时，唯一的选项是
Please select what kind of key you want:
(3) DSA (sign only)
(4) RSA (sign only)
(5) Elgamal (encrypt only)
(6) RSA (encrypt only)
从 GnuPG 2.2.6 开始，有一个隐藏的键编辑子命令“change-usage”可以做到这一点。相关提交。
让我们用测试键试试这个子命令。我们先创建一个：
mkdir /tmp/gpg-change-usage
chmod 700 /tmp/gpg-change-usage
gpg --homedir /tmp/gpg-change-usage --quick-generate-key someone@example.com rsa4096 cert 1d
现在请注意，这个新密钥是仅认证的主密钥。
$ gpg --homedir /tmp/gpg-change-usage -k
/tmp/gpg-change-usage/pubring.kbx
---------------------------------
pub rsa4096 2019-04-04 [C] [expires: 2019-04-05]
987BE3D9CF90B1C912A165734EBF4D26A937DE4C
uid [ultimate] someone@example.com
改变用法很简单：
$ gpg --homedir /tmp/gpg-change-usage --edit-key someone@example.com
gpg (GnuPG) 2.2.12; Copyright (C) 2018 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Secret key is available.
sec rsa4096/4EBF4D26A937DE4C
created: 2019-04-04 expires: 2019-04-05 usage: C
trust: ultimate validity: ultimate
[ultimate] (1). someone@example.com
gpg> change-usage
Changing usage of the primary key.
Possible actions for a RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Certify
(S) Toggle the sign capability
(E) Toggle the encrypt capability
(A) Toggle the authenticate capability
(Q) Finished
Your selection? s
Possible actions for a RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Sign Certify
(S) Toggle the sign capability
(E) Toggle the encrypt capability
(A) Toggle the authenticate capability
(Q) Finished
Your selection? q
sec rsa4096/4EBF4D26A937DE4C
created: 2019-04-04 expires: 2019-04-05 usage: SC
trust: ultimate validity: ultimate
[ultimate] (1). someone@example.com
gpg> save
现在请注意，我们的密钥获得了签名能力。
$ gpg --homedir /tmp/gpg-change-usage -k
/tmp/gpg-change-usage/pubring.kbx
---------------------------------
pub rsa4096 2019-04-04 [SC] [expires: 2019-04-05]
987BE3D9CF90B1C912A165734EBF4D26A937DE4C
uid [ultimate] someone@example.com
而已！
为了添加新的子项具有特定的用途，开始gpg2用--expert开关。然后选项是
Please select what kind of key you want:
(3) DSA (sign only)
(4) RSA (sign only)
(5) Elgamal (encrypt only)
(6) RSA (encrypt only)
(7) DSA (set your own capabilities)
(8) RSA (set your own capabilities)
Your selection?
最后两种方法允许单独切换 S、E、A 中的每一个。C 仅适用于主键，您也可以使用gpg2 --expert --gen-key. 但是，我不知道以后有什么方法可以修改使用字段。