diff --git a/README.md b/README.md index 7ca602c..fd98369 100644 --- a/README.md +++ b/README.md @@ -1,4 +1,4 @@ -This is a guide to using [YubiKey](https://www.yubico.com/products/) as a [smart card](https://security.stackexchange.com/questions/38924/how-does-storing-gpg-ssh-private-keys-on-smart-cards-compare-to-plain-usb-drives) for secure encryption, signature and authentication operations. +This is a guide to using [YubiKey](https://www.yubico.com/products/identifying-your-yubikey/) as a [smart card](https://security.stackexchange.com/questions/38924/how-does-storing-gpg-ssh-private-keys-on-smart-cards-compare-to-plain-usb-drives) for secure encryption, signature and authentication operations. Keys stored on YubiKey are [non-exportable](https://web.archive.org/web/20201125172759/https://support.yubico.com/hc/en-us/articles/360016614880-Can-I-Duplicate-or-Back-Up-a-YubiKey-), unlike filesystem-based credentials, while remaining convenient for daily use. YubiKey can be configured to require a physical touch for cryptographic operations, reducing the risk of credential compromise. @@ -6,11 +6,11 @@ To suggest an improvement, send a pull request or open an [issue](https://github - [Purchase YubiKey](#purchase-yubikey) - [Prepare environment](#prepare-environment) - * [Improving entropy](#improving-entropy) - [Install software](#install-software) - [Prepare GnuPG](#prepare-gnupg) * [Configuration](#configuration) * [Identity](#identity) + * [Key](#key) * [Expiration](#expiration) * [Passphrase](#passphrase) - [Create Certify key](#create-certify-key) @@ -19,7 +19,6 @@ To suggest an improvement, send a pull request or open an [issue](https://github - [Backup keys](#backup-keys) - [Export public key](#export-public-key) - [Configure YubiKey](#configure-yubikey) - * [Enable KDF](#enable-kdf) * [Change PIN](#change-pin) * [Set attributes](#set-attributes) - [Transfer Subkeys](#transfer-subkeys) @@ -48,10 +47,14 @@ To suggest an improvement, send a pull request or open an [issue](https://github * [Email](#email) + [Mailvelope](#mailvelope) + [Mutt](#mutt) + * [Keyserver](#keyserver) - [Updating keys](#updating-keys) * [Renew Subkeys](#renew-subkeys) * [Rotate Subkeys](#rotate-subkeys) - [Reset YubiKey](#reset-yubikey) +- [Optional hardening](#optional-hardening) + * [Improving entropy](#improving-entropy) + * [Enable KDF](#enable-kdf) - [Notes](#notes) - [Troubleshooting](#troubleshooting) - [Alternative solutions](#alternative-solutions) @@ -132,10 +135,7 @@ sd 2:0:0:0: [sdc] Attached SCSI removable disk Copy the Debian image to the device: ```console -$ sudo dd if=debian-live-*-amd64-xfce.iso of=/dev/sdc bs=4M status=progress ; sync -465+1 records in -465+1 records out -1951432704 bytes (2.0 GB, 1.8 GiB) copied, 42.8543 s, 45.5 MB/s +sudo dd if=debian-live-*-amd64-xfce.iso of=/dev/sdc bs=4M status=progress ; sync ``` **OpenBSD** @@ -151,51 +151,7 @@ $ doas dd if=debian-live-*-amd64-xfce.iso of=/dev/rsd2c bs=4m 1951432704 bytes transferred in 139.125 secs (14026448 bytes/sec) ``` -Power off, then disconnect internal hard drives and all unnecessary devices, such as the wireless card. - -## Improving entropy - -Generating cryptographic keys requires high-quality [randomness](https://www.random.org/randomness/), measured as entropy. - -Most operating systems use software-based pseudorandom number generators or CPU-based hardware random number generators (HRNG). - -Optionally, a device such as [OneRNG](https://onerng.info/onerng/) may be used to [increase the speed](https://lwn.net/Articles/648550/) and possibly the quality of available entropy. - -Configure [rng-tools](https://wiki.archlinux.org/title/Rng-tools): - -```console -sudo apt -y install at rng-tools python3-gnupg openssl - -wget https://github.com/OneRNG/onerng.github.io/raw/master/sw/onerng_3.7-1_all.deb -``` - -Verify the package: - -```console -sha256sum onerng_3.7-1_all.deb -``` - -The value must match: - -```console -b7cda2fe07dce219a95dfeabeb5ee0f662f64ba1474f6b9dddacc3e8734d8f57 -``` - -Install the package: - -```console -sudo dpkg -i onerng_3.7-1_all.deb - -echo "HRNGDEVICE=/dev/ttyACM0" | sudo tee /etc/default/rng-tools -``` - -Insert the device and restart rng-tools: - -```console -sudo atd - -sudo service rng-tools restart -``` +Power off, disconnect internal hard drives and all unnecessary devices, such as the wireless card. # Install software @@ -213,15 +169,9 @@ sudo apt update sudo apt -y upgrade sudo apt -y install \ - wget gnupg2 gnupg-agent dirmngr \ - cryptsetup scdaemon pcscd \ - yubikey-personalization yubikey-manager -``` - -**Note** Live Ubuntu images [may require modification](https://github.com/drduh/YubiKey-Guide/issues/116) to `/etc/apt/sources.list` and may need additional packages: - -```console -sudo apt -y install libssl-dev swig libpcsclite-dev + wget gnupg2 gnupg-agent dirmngr \ + cryptsetup scdaemon pcscd \ + yubikey-personalization yubikey-manager ``` **OpenBSD** @@ -296,9 +246,9 @@ wget https://github.com/rpmsphere/noarch/raw/master/r/rpmsphere-release-38-1.noa sudo rpm -Uvh rpmsphere-release*rpm sudo dnf install \ - gnupg2 dirmngr cryptsetup gnupg2-smime \ - pcsc-tools opensc pcsc-lite secure-delete \ - pgp-tools yubikey-personalization-gui + gnupg2 dirmngr cryptsetup gnupg2-smime \ + pcsc-tools opensc pcsc-lite secure-delete \ + pgp-tools yubikey-personalization-gui ``` # Prepare GnuPG @@ -331,7 +281,6 @@ cert-digest-algo SHA512 s2k-digest-algo SHA512 s2k-cipher-algo AES256 charset utf-8 -fixed-list-mode no-comments no-emit-version no-greeting @@ -357,17 +306,27 @@ Depending on how you plan to use GnuPG, set these values respectively: IDENTITY="YubiKey User " ``` -Or use any attribute which will uniquely identity the key: +Or use any attribute which will uniquely identity the key (this may be incompatible with certain use cases): ```console IDENTITY="My Cool YubiKey - 2024" ``` +## Key + +Select the desired algorithm and key size. This guide recommends 4096-bit RSA. + +Set the value: + +```console +KEY_TYPE=rsa4096 +``` + ## Expiration Determine the desired Subkey validity duration. -Setting a key expiry forces identity and credential lifecycle management. However, setting an expiry on the primary Certify key is pointless, because it can be used to simply extend itself ([revocation certificates](https://security.stackexchange.com/questions/14718/does-openpgp-key-expiration-add-to-security/79386#79386) should be used instead). +Setting a Subkey expiry forces identity and credential lifecycle management. However, setting an expiry on the Certify key is pointless, because it can just be used to extend itself. [Revocation certificates](https://security.stackexchange.com/questions/14718/does-openpgp-key-expiration-add-to-security/79386#79386) should instead be used to revoke an identity. This guide recommends a two year expiration for Subkeys to balance security and usability, however longer durations are possible to reduce maintenance frequency. @@ -389,25 +348,19 @@ EXPIRATION=2026-05-01 ## Passphrase -Generate a passphrase, which will be used to issue the Certify key and Subkeys. - -The passphrase is recommended to consist of only uppercase letters and numbers for improved readability. [Diceware](https://secure.research.vt.edu/diceware) is another method for creating strong and memorable passphrases. +Generate a passphrase for the Certify key. It will be used infrequently to manage Subkeys and should be very strong. The passphrase is recommended to consist of only uppercase letters and numbers for improved readability. [Diceware](https://secure.research.vt.edu/diceware) is another method for creating memorable passphrases. -The following commands will generate and display a strong passphrase which avoids ambiguous characters: +The following commands will generate a strong passphrase and avoid ambiguous characters: ```console -PASS=$(LC_ALL=C tr -dc 'A-Z1-9' < /dev/urandom | \ +CERTIFY_PASS=$(LC_ALL=C tr -dc 'A-Z1-9' < /dev/urandom | \ tr -d "1IOS5U" | fold -w 30 | sed "-es/./ /"{1..26..5} | \ - cut -c2- | tr " " "-" | head -1) - -echo $PASS + cut -c2- | tr " " "-" | head -1) ; echo "$CERTIFY_PASS" ``` -Memorize the passphrase or write it in a secure location, ideally separate from the portable storage device used for key material. +Write the passphrase in a secure location, ideally separate from the portable storage device used for key material, or memorize it. -This repository includes a [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.html) template to help with transcription. Save the raw file, open it with a browser and print. Use a pen or permanent marker to select a letter or number on each row for each character in the passphrase. - -[`passphrase.csv`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.csv) can also be printed without a browser: +This repository includes a [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.html) template to help with credential transcription. Save the raw file, open it with a browser and print. Use a pen or permanent marker to select a letter or number on each row for each character in the passphrase. [`passphrase.csv`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.csv) can also be printed without a browser: ```console lp -d Printer-Name passphrase.csv @@ -415,41 +368,38 @@ lp -d Printer-Name passphrase.csv # Create Certify key -The primary key to generate is the Certify key, which will be used to issue Subkeys for encryption, signature and authentication operations. +The primary key to generate is the Certify key, which is responsible for issuing Subkeys for encryption, signature and authentication operations. The Certify key should be kept offline at all times and only accessed from a dedicated and secure environment to issue or revoke Subkeys. -This guide recommends 4096-bit RSA. Do not set an expiration date on the Certify key. +Do not set an expiration date on the Certify key. Generate the Certify key: ```console -gpg --batch --passphrase "$PASS" --quick-generate-key "$IDENTITY" \ - rsa4096 cert never +gpg --batch --passphrase "$CERTIFY_PASS" \ + --quick-generate-key "$IDENTITY" "$KEY_TYPE" cert never ``` -Set the Certify key identifier beginning with `0x` as `KEYID` with the following command, or by entering the value manually: +Set and view the Certify key identifier and fingerprint for use later: ```console -KEYID=$(gpg -K | grep -Po "(0x\w+)") -``` +KEYID=$(gpg -k --with-colons "$IDENTITY" | awk -F: '/^pub:/ { print $5; exit }') -Set the key fingerprint: +KEYFP=$(gpg -k --with-colons "$IDENTITY" | awk -F: '/^fpr:/ { print $10; exit }') -```console -KEYFPR=$(gpg --fingerprint "$KEYID" | grep -Eo '([0-9A-F][0-9A-F ]{49})' | head -n 1 | tr -d ' ') +echo $KEYID $KEYFP ``` # Create Subkeys -The following command will generate Signature, Encryption and Authentication Subkeys, using the previously configured passphrase and expiration: +Use the following command to generate Signature, Encryption and Authentication Subkeys using the previously configured key type, passphrase and expiration: ```console -for key_type in sign encrypt auth ; do \ - gpg --batch --pinentry-mode=loopback \ - --passphrase "$PASS" --quick-add-key "$KEYFPR" \ - rsa4096 $key_type "$EXPIRATION" - done +for SUBKEY in sign encrypt auth ; do \ + gpg --batch --pinentry-mode=loopback --passphrase "$CERTIFY_PASS" \ + --quick-add-key "$KEYFP" "$KEY_TYPE" "$SUBKEY" "$EXPIRATION" +done ``` # Verify keys @@ -466,31 +416,31 @@ The output will display **[C]ertify, [S]ignature, [E]ncryption and [A]uthenticat sec rsa4096/0xF0F2CFEB04341FB5 2024-01-01 [C] Key fingerprint = 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 uid [ultimate] YubiKey User -ssb rsa4096/0xB3CD10E502E19637 2024-01-01 [S] [expires: 2026-01-01] -ssb rsa4096/0x30CBE8C4B085B9F7 2024-01-01 [E] [expires: 2026-01-01] -ssb rsa4096/0xAD9E24E1B8CB9600 2024-01-01 [A] [expires: 2026-01-01] +ssb rsa4096/0xB3CD10E502E19637 2024-01-01 [S] [expires: 2026-05-01] +ssb rsa4096/0x30CBE8C4B085B9F7 2024-01-01 [E] [expires: 2026-05-01] +ssb rsa4096/0xAD9E24E1B8CB9600 2024-01-01 [A] [expires: 2026-05-01] ``` # Backup keys -Save a copy of the Certify key and Subkeys: +Save a copy of the Certify key, Subkeys and public key: ```console gpg --output $GNUPGHOME/$KEYID-Certify.key \ - --batch --pinentry-mode=loopback --passphrase "$PASS" \ + --batch --pinentry-mode=loopback --passphrase "$CERTIFY_PASS" \ --armor --export-secret-keys $KEYID gpg --output $GNUPGHOME/$KEYID-Subkeys.key \ - --batch --pinentry-mode=loopback --passphrase "$PASS" \ + --batch --pinentry-mode=loopback --passphrase "$CERTIFY_PASS" \ --armor --export-secret-subkeys $KEYID -gpg --output $GNUPGHOME/$KEYID.asc \ +gpg --output $GNUPGHOME/$KEYID-$(date +%F).asc \ --armor --export $KEYID ``` Create an **encrypted** backup on portable storage to be kept offline in a secure and durable location. -The following process is recommended to be repeated several times on multiple portable storage devices, as they can fail over time. As an additional backup measure, [Paperkey](https://www.jabberwocky.com/software/paperkey/) may be used to make a physical copy of key materials for improved durability. +The following process is recommended to be repeated several times on multiple portable storage devices, as they are likely to fail over time. As an additional backup measure, [Paperkey](https://www.jabberwocky.com/software/paperkey/) can be used to make a physical copy of key materials for improved durability. **Tip** The [ext2](https://en.wikipedia.org/wiki/Ext2) filesystem without encryption can be mounted on Linux and OpenBSD. Use [FAT32](https://en.wikipedia.org/wiki/Fat32) or [NTFS](https://en.wikipedia.org/wiki/Ntfs) filesystem for macOS and Windows compatibility instead. @@ -507,7 +457,7 @@ $ sudo fdisk -l /dev/sdc Disk /dev/sdc: 14.9 GiB, 15931539456 bytes, 31116288 sectors ``` -**Warning** Confirm the destination (`of`) before issuing the following command! This guide uses `/dev/sdc` throughout, but this value may differ on your system. +**Warning** Confirm the destination (`of`) before issuing the following command - it is destructive! This guide uses `/dev/sdc` throughout, but this value may be different on your system. Zero the header to prepare for encryption: @@ -536,28 +486,30 @@ w EOF ``` -Use [LUKS](https://askubuntu.com/questions/97196/how-secure-is-an-encrypted-luks-filesystem) to encrypt the new partition. +Use [LUKS](https://dys2p.com/en/2023-05-luks-security.html) to encrypt the new partition. -Once again, generate a unique passphrase (different from the [Passphrase](#passphrase) used for the GnuPG identity) to protect the encrypted volume: +Generate another unique [Passphrase](#passphrase) (ideally different from the one used for the Certify key) to protect the encrypted volume: ```console -PASS=$(LC_ALL=C tr -dc 'A-Z1-9' < /dev/urandom | \ +LUKS_PASS=$(LC_ALL=C tr -dc 'A-Z1-9' < /dev/urandom | \ tr -d "1IOS5U" | fold -w 30 | sed "-es/./ /"{1..26..5} | \ - cut -c2- | tr " " "-" | head -1) - -echo $PASS + cut -c2- | tr " " "-" | head -1) ; echo $LUKS_PASS ``` -Memorize or write it down, then format the partition: +This passphrase will also be used infrequently to access the Certify key and should be very strong. + +Write the passphrase down or memorize it. + +Format the partition: ```console -echo $PASS | sudo cryptsetup -q luksFormat /dev/sdc1 +echo $LUKS_PASS | sudo cryptsetup -q luksFormat /dev/sdc1 ``` Mount the partition: ```console -echo $PASS | sudo cryptsetup -q luksOpen /dev/sdc1 gnupg-secrets +echo $LUKS_PASS | sudo cryptsetup -q luksOpen /dev/sdc1 gnupg-secrets ``` Create an ext2 filesystem: @@ -566,7 +518,7 @@ Create an ext2 filesystem: sudo mkfs.ext2 /dev/mapper/gnupg-secrets -L gnupg-$(date +%F) ``` -Mount the filesystem and copy the temporary GnuPG working directory exported key materials: +Mount the filesystem and copy the temporary GnuPG working directory with key materials: ```console sudo mkdir /mnt/encrypted-storage @@ -576,14 +528,6 @@ sudo mount /dev/mapper/gnupg-secrets /mnt/encrypted-storage sudo cp -av $GNUPGHOME /mnt/encrypted-storage/ ``` -**Optional** Backup the OneRNG package: - -```console -sudo cp onerng_3.7-1_all.deb /mnt/encrypted-storage/ -``` - -**Note** To provision multiple YubiKeys, keep the backup mounted or remember to terminate the GnuPG process before [saving](https://lists.gnupg.org/pipermail/gnupg-users/2016-July/056353.html). - Unmount and close the encrypted volume: ```console @@ -592,6 +536,8 @@ sudo umount /mnt/encrypted-storage sudo cryptsetup luksClose gnupg-secrets ``` +Repeat the process for any additional storage devices (at least two are recommended). + **OpenBSD** Attach a USB disk and determine its label: @@ -664,9 +610,7 @@ doas mount /dev/sd3i /mnt/encrypted-storage doas cp -av $GNUPGHOME /mnt/encrypted-storage ``` -**Note** To set up multiple YubiKeys, keep the backup mounted or terminate GnuPG before [saving](https://lists.gnupg.org/pipermail/gnupg-users/2016-July/056353.html). - -Otherwise, unmount and disconnect the encrypted volume: +Unmount and disconnect the encrypted volume: ```console doas umount /mnt/encrypted-storage @@ -680,7 +624,7 @@ See [OpenBSD FAQ#14](https://www.openbsd.org/faq/faq14.html#softraidCrypto) for **Important** Without the public key, it will **not** be possible to use GnuPG to decrypt nor sign messages. However, YubiKey can still be used for SSH authentication. -Create another partition on the portable storage device to store the public key, or reconnect networking and upload to a key server. +Connect another portable storage device or create a new partition on the existing one. **Linux** @@ -707,7 +651,7 @@ sudo mount /dev/sdc2 /mnt/public gpg --armor --export $KEYID | sudo tee /mnt/public/$KEYID-$(date +%F).asc -sudo chmod 0444 /mnt/public/0x*.asc +sudo chmod 0444 /mnt/public/*.asc ``` Unmount and remove the storage device: @@ -742,39 +686,25 @@ doas mount /dev/sd2b /mnt/public gpg --armor --export $KEYID | doas tee /mnt/public/$KEYID-$(date +%F).asc ``` -**Windows** +Unmount and remove the storage device: ```console -gpg -o \path\to\dir\pubkey.gpg --armor --export $KEYID +doas umount /mnt/public ``` # Configure YubiKey -If the card is locked, [Reset](#reset) it. - -**Windows** Use the [YubiKey Manager](https://developers.yubico.com/yubikey-manager) application (note, this is not the similarly named older YubiKey NEO Manager) to enable CCID functionality. - -## Enable KDF - -Key Derived Function (KDF) enables YubiKey to store the hash of PIN, preventing the PIN from being passed as plain text. - -**Note** This feature may not be compatible with older GnuPG versions, especially mobile clients. These incompatible clients will not function because the PIN will always be rejected. - -Enable KDF using the default Admin pin of `12345678`: +Connect YubiKey and confirm its status: ```console -gpg --command-fd=0 --pinentry-mode=loopback --card-edit <`, for sec rsa4096/0xF0F2CFEB04341FB5 2024-01-01 [C] Key fingerprint = 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 uid [ultimate] YubiKey User -ssb> rsa4096/0xB3CD10E502E19637 2024-01-01 [S] [expires: 2026-01-01] -ssb> rsa4096/0x30CBE8C4B085B9F7 2024-01-01 [E] [expires: 2026-01-01] -ssb> rsa4096/0xAD9E24E1B8CB9600 2024-01-01 [A] [expires: 2026-01-01] +ssb> rsa4096/0xB3CD10E502E19637 2024-01-01 [S] [expires: 2026-05-01] +ssb> rsa4096/0x30CBE8C4B085B9F7 2024-01-01 [E] [expires: 2026-05-01] +ssb> rsa4096/0xAD9E24E1B8CB9600 2024-01-01 [A] [expires: 2026-05-01] ``` -A `>` after a tag indicates the key is stored on a smart card. +The `>` after a tag indicates the key is stored on a smart card. # Finish setup Verify you have done the following: - [ ] Memorized or wrote down the Certify key passphrase to a secure and durable location -- [ ] Saved the Certify key and Subkeys to encrypted portable storage, to be kept offline + * `echo $CERTIFY_PASS` to see it again; [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.html) or [`passphrase.csv`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.csv) to transcribe it - [ ] Memorized or wrote down passphrase to encrypted volume on portable storage + * `echo $LUKS_PASS` to see it again; [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.html) or [`passphrase.csv`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.csv) to transcribe it +- [ ] Saved the Certify key and Subkeys to encrypted portable storage, to be kept offline + * At least two backups are recommended, stored at separate locations - [ ] Exported a copy of the public key where is can be easily accessed later -- [ ] Memorized or wrote down the User Pin and Admin PIN, which are unique and changed from default values -- [ ] Moved Encryption, Signature and Authentication Subkeys to YubiKey (`gpg -K` shows `ssb>` for 3 Subkeys) + * Separate device or non-encrypted partition was used +- [ ] Memorized or wrote down the User PIN and Admin PIN, which are unique and changed from default values + * `echo $USER_PIN $ADMIN_PIN` to see them again; [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.html) or [`passphrase.csv`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/master/passphrase.csv) to transcribe them +- [ ] Moved Encryption, Signature and Authentication Subkeys to YubiKey + * `gpg -K` shows `ssb>` for each of the 3 Subkeys Reboot to clear the ephemeral environment and complete setup. -The YubiKey(s) are now ready for use. - # Using YubiKey Initialize GnuPG: @@ -948,7 +882,7 @@ cd ~/.gnupg wget https://raw.githubusercontent.com/drduh/config/master/gpg.conf ``` -Set the following option. This avoids the problem where GnuPG will prompt, repeatedly, for the insertion of an already-inserted YubiKey: +Set the following option. This avoids the problem where GnuPG will repeatedly prompt for the insertion of an already-inserted YubiKey: ```console touch scdaemon.conf @@ -956,22 +890,19 @@ touch scdaemon.conf echo "disable-ccid" >>scdaemon.conf ``` -> The `disable-ccid` option is only required for GnuPG versions 2.3 or later. However, setting this option does not appear to interfere with the operation of earlier versions of GnuPG so it is recommended for all installations. - Install the required packages: -**Debian and Ubuntu** +**Debian/Ubuntu** ```console sudo apt update -sudo apt install -y gnupg2 gnupg-agent gnupg-curl scdaemon pcscd +sudo apt install -y \ + gnupg gnupg-agent gnupg-curl scdaemon pcscd ``` **OpenBSD** -Requires a reboot. - ```console doas pkg_add gnupg pcsc-tools @@ -982,16 +913,26 @@ doas reboot Mount the non-encrypted volume with the public key: +**Debian/Ubuntu** + +```console +sudo mkdir /mnt/public + +sudo mount /dev/sdc2 /mnt/public +``` + +**OpenBSD** + ```console doas mkdir /mnt/public doas mount /dev/sd3i /mnt/public ``` -Import it: +Import the public key: ```console -gpg --import /mnt/public/0x*.asc +gpg --import /mnt/public/*.asc ``` Or download the public key from a keyserver: @@ -1011,6 +952,8 @@ gpg/card> quit Determine the key ID: ```console +gpg -k + KEYID=0xF0F2CFEB04341FB5 ``` @@ -1027,7 +970,7 @@ EOF Remove and re-insert YubiKey. -Verify the status with `gpg --card-status` which will be similar to: +Verify the status with `gpg --card-status` which will list the available Subkeys: ```console Reader ...........: Yubico YubiKey OTP FIDO CCID 00 00 @@ -1055,17 +998,17 @@ Authentication key: 570E 1355 6D01 4C04 8B6D E2A3 AD9E 24E1 B8CB 9600 created ....: 2024-01-01 12:00:00 General key info..: sub rsa4096/0xB3CD10E502E19637 2024-01-01 YubiKey User sec# rsa4096/0xF0F2CFEB04341FB5 created: 2024-01-01 expires: never -ssb> rsa4096/0xB3CD10E502E19637 created: 2024-01-01 expires: 2026-01-01 +ssb> rsa4096/0xB3CD10E502E19637 created: 2024-01-01 expires: 2026-05-01 card-no: 0006 05553211 -ssb> rsa4096/0x30CBE8C4B085B9F7 created: 2024-01-01 expires: 2026-01-01 +ssb> rsa4096/0x30CBE8C4B085B9F7 created: 2024-01-01 expires: 2026-05-01 card-no: 0006 05553211 -ssb> rsa4096/0xAD9E24E1B8CB9600 created: 2024-01-01 expires: 2026-01-01 +ssb> rsa4096/0xAD9E24E1B8CB9600 created: 2024-01-01 expires: 2026-05-01 card-no: 0006 05553211 ``` `sec#` indicates the corresponding key is not available (the Certify key is offline). -**Note** If `General key info..: [none]` appears in the output instead - go back and import the public key using the previous step. +YubiKey is now ready for use! ## Encryption @@ -1073,22 +1016,23 @@ Encrypt a message to yourself (useful for storing credentials or protecting back ```console echo "\ntest message string" | \ - gpg --encrypt --armor --recipient $KEYID -o encrypted.txt + gpg --encrypt --armor \ + --recipient $KEYID --output encrypted.txt ``` -To encrypt to multiple recipients or keys (the preferred key ID goes last): +Decrypt the message - a prompt for the User PIN will appear: ```console -echo "test message string" | \ - gpg --encrypt --armor \ - --recipient $KEYID_0 --recipient $KEYID_1 --recipient $KEYID_2 \ - -o encrypted.txt +gpg --decrypt --armor encrypted.txt ``` -Decrypt the message - a User PIN prompt will appear: +To encrypt to multiple recipients/keys (set the preferred key ID last): ```console -gpg --decrypt --armor encrypted.txt +echo "test message string" | \ + gpg --encrypt --armor \ + --recipient $KEYID_2 --recipient $KEYID_1 --recipient $KEYID \ + --output encrypted.txt ``` Use a [shell function](https://github.com/drduh/config/blob/master/zshrc) to make encrypting files easier: @@ -1148,11 +1092,9 @@ Primary key fingerprint: 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 ## Configure touch -**Note** This is not possible on YubiKey NEO. - By default, YubiKey will perform cryptographic operations without requiring any action from the user after the key is unlocked once with the PIN. -To require a touch for each key operation, use [YubiKey Manager](https://developers.yubico.com/yubikey-manager/) and the Admin PIN to set policy: +To require a touch for each key operation, use [YubiKey Manager](https://developers.yubico.com/yubikey-manager/) and the Admin PIN to set key policy. Encryption: @@ -1160,7 +1102,13 @@ Encryption: ykman openpgp keys set-touch dec on ``` -**Note** Versions of YubiKey Manager before 5.1.0 use `enc` instead of `dec` for encryption. Older versions of YubiKey Manager use `touch` instead of `set-touch` +**Note** Versions of YubiKey Manager before 5.1.0 use `enc` instead of `dec` for encryption: + +```console +ykman openpgp keys set-touch enc on +``` + +Even older versions of YubiKey Manager use `touch` instead of `set-touch` Signature: @@ -1298,6 +1246,7 @@ Restart the agent: ```console gpg-connect-agent killagent /bye + gpg-connect-agent /bye ``` @@ -1651,7 +1600,7 @@ extra-socket /run/user/1000/gnupg/S.gpg-agent.extra **Important** Any pinentry program except `pinentry-tty` or `pinentry-curses` may be used. This is because local `gpg-agent` may start headlessly (by systemd without `$GPG_TTY` set locally telling which tty it is on), thus failed to obtain the pin. Errors on the remote may be misleading saying that there is *IO Error*. (Yes, internally there is actually an *IO Error* since it happens when writing to/reading from tty while finding no tty to use, but for end users this is not friendly.) -See [Issue #85](https://github.com/drduh/YubiKey-Guide/issues/85) for more information and troubleshooting. +See [Issue 85](https://github.com/drduh/YubiKey-Guide/issues/85) for more information and troubleshooting. ### Chained GnuPG agent forwarding @@ -1832,20 +1781,22 @@ cd $GNUPGHOME cp -avi /mnt/encrypted-storage/gnupg-*/* $GNUPGHOME ``` -Confirm the identity is available, set it and the key fingerprint: +Confirm the identity is available, set the key id and fingerprint: ```console gpg -K -KEYID=$(gpg -K | grep -Po "(0x\w+)" | head -1) +KEYID=$(gpg -k --with-colons "$IDENTITY" | awk -F: '/^pub:/ { print $5; exit }') -KEYFPR=$(gpg --fingerprint "$KEYID" | grep -Eo '([0-9A-F][0-9A-F ]{49})' | head -n 1 | tr -d ' ') +KEYFP=$(gpg -k --with-colons "$IDENTITY" | awk -F: '/^fpr:/ { print $10; exit }') + +echo $KEYID $KEYFP ``` -Recall the identity passphrase and set it, for example: +Recall the Certify key passphrase and set it, for example: ```console -PASS=ABCD-0123-IJKL-4567-QRST-UVWX +CERTIFY_PASS=ABCD-0123-IJKL-4567-QRST-UVWX ``` ## Renew Subkeys @@ -1862,7 +1813,7 @@ Renew the Subkeys: ```console gpg --batch --pinentry-mode=loopback \ - --passphrase "$PASS" --quick-set-expire "$KEYFPR" "$EXPIRATION" "*" + --passphrase "$CERTIFY_PASS" --quick-set-expire "$KEYFP" "$EXPIRATION" "*" ``` Export the updated public key: @@ -1874,7 +1825,7 @@ gpg --armor --export $KEYID | sudo tee /mnt/public/$KEYID-$(date +%F).asc Transfer the public key to the destination host and import it: ```console -gpg --import 0x*.asc +gpg --import /mnt/public/*.asc ``` Alternatively, publish to a public key server and download it: @@ -1962,6 +1913,70 @@ Reset code: NOT SET Admin PIN: 12345678 ``` +# Optional hardening + +The following steps may improve the security and privacy of YubiKey. + +## Improving entropy + +Generating cryptographic keys requires high-quality [randomness](https://www.random.org/randomness/), measured as entropy. Most operating systems use software-based pseudorandom number generators or CPU-based hardware random number generators (HRNG). + +Optionally, a device such as [OneRNG](https://onerng.info/onerng/) may be used to [increase the speed](https://lwn.net/Articles/648550/) and possibly the quality of available entropy. + +Before creating keys, configure [rng-tools](https://wiki.archlinux.org/title/Rng-tools): + +```console +sudo apt -y install at rng-tools python3-gnupg openssl + +wget https://github.com/OneRNG/onerng.github.io/raw/master/sw/onerng_3.7-1_all.deb +``` + +Verify the package: + +```console +sha256sum onerng_3.7-1_all.deb +``` + +The value must match: + +```console +b7cda2fe07dce219a95dfeabeb5ee0f662f64ba1474f6b9dddacc3e8734d8f57 +``` + +Install the package: + +```console +sudo dpkg -i onerng_3.7-1_all.deb + +echo "HRNGDEVICE=/dev/ttyACM0" | sudo tee /etc/default/rng-tools +``` + +Insert the device and restart rng-tools: + +```console +sudo atd + +sudo service rng-tools restart +``` + +## Enable KDF + +**Note** This feature may not be compatible with older GnuPG versions, especially mobile clients. These incompatible clients will not function because the PIN will always be rejected. + +This step must be completed before changing PINs or moving keys or an error will occur: `gpg: error for setup KDF: Conditions of use not satisfied` + +Key Derived Function (KDF) enables YubiKey to store the hash of PIN, preventing the PIN from being passed as plain text. + +Enable KDF using the default Admin PIN of `12345678`: + +```console +gpg --command-fd=0 --pinentry-mode=loopback --card-edit <