GnuPG (正體中文)

相關文章

• pacman/Package signing
• Disk encryption
• List of applications/Security#Encryption, signing, steganography

翻譯狀態：本文章是 GnuPG 的翻譯版本。最近一次的翻譯時間：2017-12-02。點擊本連結查看英文頁面之後的變更。

根據 official website:

GnuPG 是根據OpenPGP（亦稱作PGP的）所制定之RFC4880標準的一個完整且自由的軟體。

GnuPG讓你可以可以加密及簽署你的檔案及通認資料，其特色在於豐富的金鑰管理系統及多種公鑰連接模組。作為一個命令列工具可輕易的與其他硬用程式整合，因此有豐富的應用程式與函式庫。此外GnuPG第二版更支援S/MIME及Secure Shell（ssh）。

安裝

Install the package. 安裝gnupg同時，pinentry也會被一併安裝，pinentry是使用GPG時要求輸入密碼的對話視窗程式，連結為/usr/bin/pinentry而預設是/usr/bin/pinentry-gtk-2。若你想採用整合GnuPG其他圖形化介面的程式可參考此列表List of applications/Security#Encryption, signing, steganography。

配置

資料夾位置

GnuPG的設定檔存於$GNUPGHOME，$GNUPGHOME並沒有預設路徑，在此情形下則會使用$HOME。因此，你在安裝後將會發現~/.gnupg這個資料夾。

如果需要修改預設路徑，可以執行$ gpg --homedir path/to/file，或在startup files設定GNUPGHOME。

設定檔

~/.gnupg/gpg.conf及~/.gnupg/dirmngr.conf為預設設定檔。

gnupg資料來預設為700權限，而裡面的檔案則為600權限。只有該資料夾的擁有者有權讀取、修改、及存取該等檔案。這些權限設定基於安全考量不應輕易修改。如果這些檔案不符合這個安全規範時，gnppg會產生關於檔案或gnupg家目錄不安全權限的警告。

加入的文件雖然可以為任意長度，但不要有兩個破折號（-），建議為選項名稱和使用的參數。你可以在/usr/share/gnupg找到一些範例檔案。在gpg第一次執行且沒有檔案時，其亦會將這些範例檔案複製至~/.gnupg 。你也可以在#參考文件中找到一些範例。

此外，pacman採用不同組的設定檔，其用於軟體簽章的驗証。更細節部份可參考Pacman/Package signing。

新使用者的預設參數

如果你想為新使用者設定預設參數，可將設定檔放置於/etc/skel/.gnupg/。一旦新使用者加入系統時，該等檔案將會自動地複製到使用者的GnuPG家目錄。此外，addgnupghome 這個指令可以協助你為已存在的使用者新增GnuPG家目錄。

# addgnupghome user1 user2

此指令將會各別生成/home/user1/.gnupg和/home/user2/.gnupg，並且從樣版資料夾中複製檔案，但若使用者已先產生GnuPG家目錄，則不會有改動。

使用方法

註記: 無論指令執行時是否可以獲取user-id，請在指令執行時給予key ID、指紋、你的名字或email，而GnuPG會自動判斷你給的資訊。

建立鑰匙

藉由以下指令產生一對鑰匙：

$ gpg --full-gen-key

提示: 可加入--expert 選擇不同的加密方式，例如：ECC.

這個指令會有一些問題跟提示，大部分的使用者可參考如下設定：

• RSA (sign only) 或 RSA (encrypt only) key.
• keysize建議值為2048，4096並不會有額外的好處但卻更耗損資源，請參[1]。
• 設定過期時間，建議一年，在屆滿時可以再行延展而不用重新產生鑰匙。
• 你的名字跟email設定，你也可以將多個email綁在同一對鑰匙上。
• 如果需要設定額外註釋請參考TOFU Design，但並不建議填寫。
• 密碼可參考a secure passphrase.

註記: 名字與email將會被人往後匯入你的公鑰的人看到。

List keys

To list keys in your public key ring:

$ gpg --list-keys

To list keys in your secret key ring:

$ gpg --list-secret-keys

Export your public key

gpg's main usage is to ensure confidentiality of exchanged messages via public-key cryptography. With it each user distributes the public key of their keyring, which can be be used by others to encrypt messages to the user. The private key must always be kept private, otherwise confidentiality is broken. See w:Public-key cryptography for examples about the message exchange.

So, in order for others to send encrypted messages to you, they need your public key.

To generate an ASCII version of a user's public key to file public.key (e.g. to distribute it by e-mail):

$ gpg --output public.key --armor --export user-id

Alternatively, or in addition, you can #Use a keyserver to share your key.

提示: Add --no-emit-version to avoid printing the version number, or add the corresponding setting to your configuration file.

Import a public key

In order to encrypt messages to others, as well as verify their signatures, you need their public key. To import a public key with file name public.key to your public key ring:

$ gpg --import public.key

Alternatively, #Use a keyserver to find a public key.

Use a keyserver

You can register your key with a public PGP key server, so that others can retrieve your key without having to contact you directly:

$ gpg --send-keys user-id

To find out details of a key on the keyserver, without importing it, do:

$ gpg --search-keys user-id

To import a key from a key server:

$ gpg --recv-keys key-id

警告:

• You should verify the authenticity of the retrieved public key by comparing its fingerprint with one that the owner published on an independent source(s) (i.e., contacting the person directly). See Wikipedia:Public key fingerprint for more information.
• Using a short ID may encounter collisions. All keys will be imported that have the short ID. To avoid this, use the full fingerprint or long key ID when receiving a key.[2]

提示:

• Adding keyserver-options auto-key-retrieve to gpg.conf will automatically fetch keys from the key server as needed.
• An alternative key server is pool.sks-keyservers.net and can be specified with keyserver in dirmngr.conf; see also wikipedia:Key server (cryptographic)#Keyserver examples.
• If your network blocks ports used for hkp/hkps, you may need to specify port 80, i.e. pool.sks-keyservers.net:80
• You can connect to the keyserver over Tor using --use-tor. See this GnuPG blog post for more information.
• You can connect to a keyserver using a proxy by setting the http_proxy environment variable and setting honor-http-proxy in dirmngr.conf. Alternatively, set http-proxy host[:port] in dirmngr.conf, overriding the http_proxy environment variable.
• If you wish to import a key ID to install a specific Arch Linux package, see pacman/Package signing#Managing the keyring and Makepkg#Signature checking.

Encrypt and decrypt

Asymmetric

You need to #Import a public key of a user before encrypting (options --encrypt or -e) a file or message to that recipient (options --recipient or -r). Additionally you need to #Create key pair^{[broken link: invalid section]} if you have not already done so.

To encrypt a file with the name doc, use:

$ gpg --recipient user-id --encrypt doc

To decrypt (option --decrypt or -d) a file with the name doc.gpg encrypted with your public key, use:

$ gpg --output doc --decrypt doc.gpg

gpg will prompt you for your passphrase and then decrypt and write the data from doc.gpg to doc. If you omit the -o (--output) option, gpg will write the decrypted data to stdout.

提示:

• Add --armor to encrypt a file using ASCII armor (suitable for copying and pasting a message in text format)
• Use -R user-id or --hidden-recipient user-id instead of -r to not put the recipient key IDs in the encrypted message. This helps to hide the receivers of the message and is a limited countermeasure against traffic analysis.
• Add --no-emit-version to avoid printing the version number, or add the corresponding setting to your configuration file.
• You can use gnupg to encrypt your sensitive documents by using your own user-id as recipient or by using the --default-recipient-self flag instead; however, you can only do this one file at a time, although you can always tarball various files and then encrypt the tarball. See also Disk encryption#Available methods if you want to encrypt directories or a whole file-system.

Symmetric

Symmetric encryption does not require the generation of a key pair and can be used to simply encrypt data with a passphrase. Simply use --symmetric or -c to perform symmetic encryption:

$ gpg -c doc

The following example:

• Encrypts doc with a symmetric cipher using a passphrase
• Uses the AES-256 cipher algorithm to encrypt the passphrase
• Uses the SHA-512 digest algorithm to mangle the passphrase
• Mangles the passphrase for 65536 iterations

$ gpg -c --s2k-cipher-algo AES256 --s2k-digest-algo SHA512 --s2k-count 65536 doc

To decrypt a symmetrically encrypted doc.gpg using a passphrase and output decrypted contents into the same directory as doc do:

$ gpg --output doc --decrypt doc.gpg

Key maintenance

Backup your private key

To backup your private key do the following:

$ gpg --export-secret-keys --armor <user-id> > privkey.asc

Note that gpg release 2.1 changed default behaviour so that the above command enforces a passphrase protection, even if you deliberately chose not to use one on key creation. This is because otherwise anyone who gains access to the above exported file would be able to encrypt and sign documents as if they were you without needing to know your passphrase.

警告: The passphrase is usually the weakest link in protecting your secret key. Place the private key in a safe place on a different system/device, such as a locked container or encrypted drive. It is the only safety you have to regain control to your keyring in case of, for example, a drive failure, theft or worse.

To import the backup of your private key:

$ gpg --import privkey.asc

Edit your key

Running the gpg --edit-key <user-id> command will present a menu which enables you to do most of your key management related tasks.

Some useful commands in the edit key sub menu:

> passwd       # change the passphrase
> clean        # compact any user ID that is no longer usable (e.g revoked or expired)
> revkey       # revoke a key
> addkey       # add a subkey to this key
> expire       # change the key expiration time

Type help in the edit key sub menu for more commands.

提示: If you have multiple email accounts you can add each one of them as an identity, using adduid command. You can then set your favourite one as primary.

Exporting subkey

If you plan to use the same key across multiple devices, you may want to strip out your master key and only keep the bare minimum encryption subkey on less secure systems.

First, find out which subkey you want to export.

$ gpg -K

Select only that subkey to export.

$ gpg -a --export-secret-subkeys [subkey id]! > /tmp/subkey.gpg

警告: If you forget to add the !, all of your subkeys will be exported.

At this point you could stop, but it is most likely a good idea to change the passphrase as well. Import the key into a temporary folder.

$ gpg --homedir /tmp/gpg --import /tmp/subkey.gpg
$ gpg --homedir /tmp/gpg --edit-key <user-id>
> passwd
> save
$ gpg --homedir /tmp/gpg -a --export-secret-subkeys [subkey id]! > /tmp/subkey.altpass.gpg

註記: You will get a warning that the master key was not available and the password was not changed, but that can safely be ignored as the subkey password was.

At this point, you can now use /tmp/subkey.altpass.gpg on your other devices.

Rotating subkeys

警告: Never delete your expired or revoked subkeys unless you have a good reason. Doing so will cause you to lose the ability to decrypt files encrypted with the old subkey. Please only delete expired or revoked keys from other users to clean your keyring.

If you have set your subkeys to expire after a set time, you can create new ones. Do this a few weeks in advance to allow others to update their keyring.

提示: You do not need to create a new key simply because it is expired. You can extend the expiration date.

Create new subkey (repeat for both signing and encrypting key)

$ gpg --edit-key <user-id>
> addkey

And answer the following questions it asks (see #Create key pair^{[broken link: invalid section]} for suggested settings).

Save changes

> save

Update it to a keyserver.

$ gpg --keyserver pgp.mit.edu --send-keys <user-id>

提示: Revoking expired subkeys is unnecessary and arguably bad form. If you are constantly revoking keys, it may cause others to lack confidence in you.

Signatures

Signatures certify and timestamp documents. If the document is modified, verification of the signature will fail. Unlike encryption which uses public keys to encrypt a document, signatures are created with the user's private key. The recipient of a signed document then verifies the signature using the sender's public key.

Create a signature

Sign a file

To sign a file use the --sign or -s flag:

 $ gpg --output doc.sig --sign doc

doc.sig contains both the compressed content of the original file doc and the signature in a binary format, but the file is not encrypted. However, you can combine signing with encrypting.

Clearsign a file or message

To sign a file without compressing it into binary format use:

 $ gpg --output doc.sig --clearsign doc

Here both the content of the original file doc and the signature are stored in human-readable form in doc.sig.

Make a detached signature

To create a separate signature file to be distributed separately from the document or file itself, use the --detach-sig flag:

 $ gpg --output doc.sig --detach-sig doc

Here the signature is stored in doc.sig, but the contents of doc are not stored in it. This method is often used in distributing software projects to allow users to verify that the program has not been modified by a third party.

Verify a signature

To verify a signature use the --verify flag:

 $ gpg --verify doc.sig

where doc.sig is the signed file containing the signature you wish to verify.

If you are verifying a detached signature, both the signed data file and the signature file must be present when verifying. For example, to verify Arch Linux's latest iso you would do:

 $ gpg --verify archlinux-version.iso.sig

where archlinux-version.iso must be located in the same directory.

You can also specify the signed data file with a second argument:

 $ gpg --verify archlinux-version.iso.sig /path/to/archlinux-version.iso

If a file as been encrypted in addition to being signed, simply decrypt the file and its signature will also be verified.

gpg-agent

gpg-agent is mostly used as daemon to request and cache the password for the keychain. This is useful if GnuPG is used from an external program like a mail client. gnupg comes with systemd user sockets which are enabled by default. These sockets are gpg-agent.socket, gpg-agent-extra.socket, gpg-agent-browser.socket, gpg-agent-ssh.socket, and dirmngr.socket.

• The main gpg-agent.socket is used by gpg to connect to the gpg-agent daemon.
• The intended use for the gpg-agent-extra.socket on a local system is to set up a Unix domain socket forwarding from a remote system. This enables to use gpg on the remote system without exposing the private keys to the remote system. See gpg-agent(1) for details.
• The gpg-agent-ssh.socket can be used by SSH to cache SSH keys added by the ssh-add program. See #SSH agent for the necessary configuration.
• The dirmngr.socket starts a GnuPG daemon handling connections to keyservers.

註記: If you use non-default GnuPG #Directory location^{[broken link: invalid section]}, you will need to edit all socket files to use the path in the socket directory that gpgconf --create-socketdir creates.

Configuration

gpg-agent can be configured via ~/.gnupg/gpg-agent.conf file. The configuration options are listed in gpg-agent(1). For example you can change cache ttl for unused keys:

~/.gnupg/gpg-agent.conf

default-cache-ttl 3600

提示: To cache your passphrase for the whole session, please run the following command:

$ /usr/lib/gnupg/gpg-preset-passphrase --preset XXXXXX

where XXXX is the keygrip. You can get its value when running gpg --with-keygrip -K. Passphrase will be stored until gpg-agent is restarted. If you set up default-cache-ttl value, it will take precedence.

Reload the agent

After changing the configuration, reload the agent using gpg-connect-agent:

$ gpg-connect-agent reloadagent /bye

The command should print OK.

However in some cases only the restart may not be sufficient, like when keep-screen has been added to the agent configuration. In this case you firstly need to kill the ongoing gpg-agent process and then you can restart it as was explained above.

pinentry

Finally, the agent needs to know how to ask the user for the password. This can be set in the gpg-agent configuration file.

The default uses a gtk dialog. There are other options - see info pinentry. To change the dialog implementation set pinentry-program configuration option:

~/.gnupg/gpg-agent.conf

# PIN entry program
# pinentry-program /usr/bin/pinentry-curses
# pinentry-program /usr/bin/pinentry-qt
# pinentry-program /usr/bin/pinentry-kwallet

pinentry-program /usr/bin/pinentry-gtk-2

提示: For using /usr/bin/pinentry-kwallet you have to install the kwalletcli^AUR package.

After making this change, reload the gpg-agent.

Unattended passphrase

Starting with GnuPG 2.1.0 the use of gpg-agent and pinentry is required, which may break backwards compatibility for passphrases piped in from STDIN using the --passphrase-fd 0 commandline option. In order to have the same type of functionality as the older releases two things must be done:

First, edit the gpg-agent configuration to allow loopback pinentry mode:

~/.gnupg/gpg-agent.conf

allow-loopback-pinentry

Restart the gpg-agent process if it is running to let the change take effect.

Second, either the application needs to be updated to include a commandline parameter to use loopback mode like so:

$ gpg --pinentry-mode loopback ...

...or if this is not possible, add the option to the configuration:

~/.gnupg/gpg.conf

pinentry-mode loopback

註記: The upstream author indicates setting pinentry-mode loopback in gpg.conf may break other usage, using the commandline option should be preferred if at all possible. [3]

SSH agent

gpg-agent has OpenSSH agent emulation. If you already use the GnuPG suite, you might consider using its agent to also cache your SSH keys. Additionally, some users may prefer the PIN entry dialog GnuPG agent provides as part of its passphrase management.

To start using GnuPG agent for your SSH keys, enable SSH support in the ~/.gnupg/gpg-agent.conf file:

~/.gnupg/gpg-agent.conf

enable-ssh-support

Then set SSH_AUTH_SOCK so that SSH will use gpg-agent instead of ssh-agent. To make sure each process can find your gpg-agent instance regardless of e.g. the type of shell it is child of use pam_env.

~/.pam_environment

SSH_AGENT_PID	DEFAULT=
SSH_AUTH_SOCK	DEFAULT="${XDG_RUNTIME_DIR}/gnupg/S.gpg-agent.ssh"

Alternatively, depend on Bash:

~/.bashrc

# Set SSH to use gpg-agent
unset SSH_AGENT_PID
if [ "${gnupg_SSH_AUTH_SOCK_by:-0}" -ne $$ ]; then
  export SSH_AUTH_SOCK="/run/user/$UID/gnupg/S.gpg-agent.ssh"
fi

註記:

• If you use non-default GnuPG #Directory location^{[broken link: invalid section]}, run gpgconf --create-socketdir to create a socket directory under /run/user/$UID/gnupg/. Otherwise the socket will be placed in the GnuPG home directory.
• The test involving the gnupg_SSH_AUTH_SOCK_by variable is for the case where the agent is started as gpg-agent --daemon /bin/sh, in which case the shell inherits the SSH_AUTH_SOCK variable from the parent, gpg-agent [4].

Also set the GPG_TTY and refresh the TTY in case user has switched into an X session as stated in gpg-agent(1). For example:

~/.bashrc

# Set GPG TTY
export GPG_TTY=$(tty)

# Refresh gpg-agent tty in case user switches into an X session
gpg-connect-agent updatestartuptty /bye >/dev/null

Once gpg-agent is running you can use ssh-add to approve keys, following the same steps as for ssh-agent. The list of approved keys is stored in the ~/.gnupg/sshcontrol file. Once your key is approved, you will get a pinentry dialog every time your passphrase is needed. You can control passphrase caching in the ~/.gnupg/gpg-agent.conf file. The following example would have gpg-agent cache your keys for 3 hours:

~/.gnupg/gpg-agent.conf

default-cache-ttl-ssh 10800
max-cache-ttl-ssh 10800

Smartcards

GnuPG uses scdaemon as an interface to your smartcard reader, please refer to the man page for details.

GnuPG only setups

註記: To allow scdaemon direct access to USB smarcard readers the optional dependency libusb-compat have to be installed

If you do not plan to use other cards but those based on GnuPG, you should check the reader-port parameter in ~/.gnupg/scdaemon.conf. The value '0' refers to the first available serial port reader and a value of '32768' (default) refers to the first USB reader.

GnuPG with pcscd (PCSC Lite)

註記: pcsclite and ccid have to be installed, and the contained systemd service pcscd.service has to be running, or the socket pcscd.socket has to be listening.

pcscd is a daemon which handles access to smartcard (SCard API). If GnuPG's scdaemon fails to connect the smartcard directly (e.g. by using its integrated CCID support), it will fallback and try to find a smartcard using the PCSC Lite driver.

Always use pcscd

If you are using any smartcard with an opensc driver (e.g.: ID cards from some countries) you should pay some attention to GnuPG configuration. Out of the box you might receive a message like this when using gpg --card-status

gpg: selecting openpgp failed: ec=6.108

By default, scdaemon will try to connect directly to the device. This connection will fail if the reader is being used by another process. For example: the pcscd daemon used by OpenSC. To cope with this situation we should use the same underlying driver as opensc so they can work well together. In order to point scdaemon to use pcscd you should remove reader-port from ~/.gnupg/scdaemon.conf, specify the location to libpcsclite.so library and disable ccid so we make sure that we use pcscd:

~/.gnupg/scdaemon.conf

pcsc-driver /usr/lib/libpcsclite.so
card-timeout 5
disable-ccid

Please check scdaemon(1) if you do not use OpenSC.

Tips and tricks

Different algorithm

You may want to use stronger algorithms:

~/.gnupg/gpg.conf

...

personal-digest-preferences SHA512
cert-digest-algo SHA512
default-preference-list SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES CAST5 ZLIB BZIP2 ZIP Uncompressed
personal-cipher-preferences TWOFISH CAMELLIA256 AES 3DES

In the latest version of GnuPG, the default algorithms used are SHA256 and AES, both of which are secure enough for most people. However, if you are using a version of GnuPG older than 2.1, or if you want an even higher level of security, then you should follow the above step.

Encrypt a password

It can be useful to encrypt some password, so it will not be written in clear on a configuration file. A good example is your email password.

First create a file with your password. You need to leave one empty line after the password, otherwise gpg will return an error message when evaluating the file.

Then run:

$ gpg -e -a -r <user-id> your_password_file

-e is for encrypt, -a for armor (ASCII output), -r for recipient user ID.

You will be left with a new your_password_file.asc file.

提示: pass automates this process.

Revoking a key

警告:

• Anybody having access to your revocation certificate can revoke your key, rendering it useless.
• Key revocation should only be performed if your key is compromised or lost, or you forget your passphrase.

Revocation certificates are automatically generated for newly generated keys, although one can be generated manually by the user later. These are located at ~/.gnupg/openpgp-revocs.d/. The filename of the certificate is the fingerprint of the key it will revoke.

To revoke your key, simply import the revocation certificate:

$ gpg --import <fingerprint>.rev

Now update the keyserver:

$ gpg --keyserver subkeys.pgp.net --send-keys <userid>

Change trust model

By default GnuPG uses the Web of Trust as the trust model. You can change this to Trust on first use by adding --trust-model=tofu when adding a key or adding this option to your GnuPG configuration file. More details are in this email to the GnuPG list.

Hide all recipient id's

By default the recipient's key ID is in the encrypted message. This can be removed at encryption time for a recipient by using hidden-recipient <user-id>. To remove it for all recipients add throw-keyids to your configuration file. This helps to hide the receivers of the message and is a limited countermeasure against traffic analysis. (Using a little social engineering anyone who is able to decrypt the message can check whether one of the other recipients is the one he suspects.) On the receiving side, it may slow down the decryption process because all available secret keys must be tried (e.g. with --try-secret-key <user-id>).

Using caff for keysigning parties

To allow users to validate keys on the keyservers and in their keyrings (i.e. make sure they are from whom they claim to be), PGP/GPG uses the Web of Trust. Keysigning parties allow users to get together at a physical location to validate keys. The Zimmermann-Sassaman key-signing protocol is a way of making these very effective. Here you will find a how-to article.

For an easier process of signing keys and sending signatures to the owners after a keysigning party, you can use the tool caff. It can be installed from the AUR with the package caff-svn^{AUR[損壞的連結: package not found]}.

To send the signatures to their owners you need a working MTA. If you do not have already one, install msmtp.

Always show long ID's and fingerprints

To always show long key ID's add keyid-format 0xlong to your configuration file. To always show full fingerprints of keys, add with-fingerprint to your configuration file.

Troubleshooting

Not enough random bytes available

When generating a key, gpg can run into this error:

Not enough random bytes available. Please do some other work to give the OS a chance to collect more entropy!

To check the available entropy, check the kernel parameters:

cat /proc/sys/kernel/random/entropy_avail

A healthy Linux system with a lot of entropy available will have return close to the full 4,096 bits of entropy. If the value returned is less than 200, the system is running low on entropy.

To solve it, remember you do not often need to create keys and best just do what the message suggests (e.g. create disk activity, move the mouse, edit the wiki - all will create entropy). If that does not help, check which service is using up the entropy and consider stopping it for the time. If that is no alternative, see Random number generation#Alternatives.

su

When using pinentry, you must have the proper permissions of the terminal device (e.g. /dev/tty1) in use. However, with su (or sudo), the ownership stays with the original user, not the new one. This means that pinentry will fail, even as root. The fix is to change the permissions of the device at some point before the use of pinentry (i.e. using gpg with an agent). If doing gpg as root, simply change the ownership to root right before using gpg:

# chown root /dev/ttyN  # where N is the current tty

and then change it back after using gpg the first time. The equivalent is likely to be true with /dev/pts/.

註記: The owner of tty must match with the user for which pinentry is running. Being part of the group tty is not enough.

提示: If you run gpg with script it will use a new tty with the correct ownership:

# script -q -c "gpg --gen-key" /dev/null

Agent complains end of file

The default pinentry program is pinentry-gtk-2, which needs a DBus session bus to run properly. See General troubleshooting#Session permissions for details.

Alternatively, you can use pinentry-qt. See #pinentry.

KGpg configuration permissions

There have been issues with kgpg being able to access the ~/.gnupg/ options. One issue might be a result of a deprecated options file, see the bug report.

GNOME on Wayland overrides SSH agent socket

For Wayland sessions, gnome-session sets SSH_AUTH_SOCK to the standard gnome-keyring socket, $XDG_RUNTIME_DIR/keyring/ssh. This overrides any value set in ~/.pam_environmment or systemd unit files.

To disable this behavior, set the GSM_SKIP_AGENT_WORKAROUND variable:

~/.pam_environment

SSH_AGENT_PID	DEFAULT=
SSH_AUTH_SOCK	DEFAULT="${XDG_RUNTIME_DIR}/gnupg/S.gpg-agent.ssh"
GSM_SKIP_SSH_AGENT_WORKAROUND	DEFAULT="true"

mutt and gpg

To be asked for your GnuPG password only once per session, see this forum thread.

"Lost" keys, upgrading to gnupg version 2.1

When gpg --list-keys fails to show keys that used to be there, and applications complain about missing or invalid keys, some keys may not have been migrated to the new format.

Please read GnuPG invalid packet workaround. Basically, it says that there is a bug with keys in the old pubring.gpg and secring.gpg files, which have now been superseded by the new pubring.kbx file and the private-keys-v1.d/ subdirectory and files. Your missing keys can be recovered with the following commnads:

$ cd
$ cp -r .gnupg gnupgOLD
$ gpg --export-ownertrust > otrust.txt
$ gpg --import .gnupg/pubring.gpg
$ gpg --import-ownertrust otrust.txt
$ gpg --list-keys

gpg hanged for all keyservers (when trying to receive keys)

If gpg hanged with a certain keyserver when trying to receive keys, you might need to kill dirmngr in order to get access to other keyservers which are actually working, otherwise it might keeping hanging for all of them.

Smartcard not detected

Your user might not have the permission to access the smartcard which results in a card error to be thrown, even though the card is correctly set up and inserted.

One possible solution is to add a new group scard including the users who need access to the smartcard.

Then use an udev^{[broken link: invalid section]} rule, similar to the following:

/etc/udev/rules.d/71-gnupg-ccid.rules

ACTION=="add", SUBSYSTEM=="usb", ENV{ID_VENDOR_ID}=="1050", ENV{ID_MODEL_ID}=="0116|0111", MODE="660", GROUP="scard"

One needs to adapt VENDOR and MODEL according to the lsusb output, the above example is for a YubikeyNEO.

gpg: WARNING: server 'gpg-agent' is older than us (x < y)

This warning appears if gnupg is upgraded and the old gpg-agent is still running. Restart the user's gpg-agent.socket (i.e., use the --user flag when restarting).

gpg: ..., IPC connect call failed

Make sure gpg-agent and dirmngr are not running with killall gpg-agent dirmngr and the $GNUPGHOME/crls.d/ folder has permission set to 700.

If your keyring is stored on a vFat filesystem (e.g. a USB drive), gpg-agent will fail to create the required sockets (vFat does not support sockets), you can create redirects to a location that handles sockets, e.g. /dev/shm:

# export GNUPGHOME=/custom/gpg/home                                                                
# printf '%%Assuan%%\nsocket=/dev/shm/S.gpg-agent\n' > $GNUPGHOME/S.gpg-agent                      
# printf '%%Assuan%%\nsocket=/dev/shm/S.gpg-agent.browser\n' > $GNUPGHOME/S.gpg-agent.browser      
# printf '%%Assuan%%\nsocket=/dev/shm/S.gpg-agent.extra\n' > $GNUPGHOME/S.gpg-agent.extra          
# printf '%%Assuan%%\nsocket=/dev/shm/S.gpg-agent.ssh\n' > $GNUPGHOME/S.gpg-agent.ssh              

Test that gpg-agent starts successfully with gpg-agent --daemon.

Error: [key] could not be locally signed or gpg: No default secret key: No public key

Occurs when attempting to sign keys on a non-standard keyring while a yubikey is plugged in, e.g. as Pacman does in pacman-key --populate archlinux. The solution is to remove the offending yubikey and start over.

參考文件

• GNU Privacy Guard Homepage
• RFC4880 "OpenPGP Message Format"
• Creating GPG Keys (Fedora)
• OpenPGP subkeys in Debian
• A more comprehensive gpg Tutorial
• gpg.conf recommendations and best practices
• Torbirdy gpg.conf
• /r/GPGpractice - a subreddit to practice using GnuPG.