# How to encrypt, sign and decrypt messages using PGP on macOS [](https://www.youtube.com/watch?v=mE8fL5Fu8x8 "How to encrypt, sign and decrypt messages using PGP on macOS") > WARNING: this is a getting started guide. For a hardened guide, see https://github.com/drduh/YubiKey-Guide ## Setup guide ### Step 1: install [Homebrew](https://brew.sh/) ```shell /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)" ``` ### Step 2: disable Homebrew analytics ```shell brew analytics off ``` ### Step 3: install [GnuPG](https://gnupg.org/) ```shell brew install gnupg ``` ### Step 4: generate PGP key pair ```console $ gpg --full-generate-key gpg (GnuPG) 2.2.20; Copyright (C) 2020 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. gpg: directory '/Users/sunknudsen/.gnupg' created gpg: keybox '/Users/sunknudsen/.gnupg/pubring.kbx' created Please select what kind of key you want: (1) RSA and RSA (default) (2) DSA and Elgamal (3) DSA (sign only) (4) RSA (sign only) (14) Existing key from card Your selection? 1 RSA keys may be between 1024 and 4096 bits long. What keysize do you want? (2048) 4096 Requested keysize is 4096 bits Please specify how long the key should be valid. 0 = key does not expire = key expires in n days w = key expires in n weeks m = key expires in n months y = key expires in n years Key is valid for? (0) 0 Key does not expire at all Is this correct? (y/N) y GnuPG needs to construct a user ID to identify your key. Real name: John Doe Email address: john@example.net Comment: You selected this USER-ID: "John Doe " Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O We need to generate a lot of random bytes. It is a good idea to perform some other action (type on the keyboard, move the mouse, utilize the disks) during the prime generation; this gives the random number generator a better chance to gain enough entropy. We need to generate a lot of random bytes. It is a good idea to perform some other action (type on the keyboard, move the mouse, utilize the disks) during the prime generation; this gives the random number generator a better chance to gain enough entropy. gpg: /Users/sunknudsen/.gnupg/trustdb.gpg: trustdb created gpg: key 1BDC94DFB97BE4D4 marked as ultimately trusted gpg: directory '/Users/sunknudsen/.gnupg/openpgp-revocs.d' created gpg: revocation certificate stored as '/Users/sunknudsen/.gnupg/openpgp-revocs.d/F365EDCF06F4D9F09BB7D4EB1BDC94DFB97BE4D4.rev' public and secret key created and signed. pub rsa4096 2020-06-16 [SC] F365EDCF06F4D9F09BB7D4EB1BDC94DFB97BE4D4 uid John Doe sub rsa4096 2020-06-16 [E] ``` ### Step 5: set default PGP key server to `hkps://keys.openpgp.org` ```shell echo "keyserver hkps://keys.openpgp.org" >> ~/.gnupg/dirmngr.conf ``` 👍 --- ## Usage guide ### Export John’s PGP public key ```shell gpg --armor --export john@example.net > ~/Desktop/john.asc ``` ### Import Sun’s PGP public key ```shell gpg --keyserver hkps://keys.openpgp.org --recv-keys 0xC1323A377DE14C8B ``` or ```shell curl https://sunknudsen.com/sunknudsen.asc | gpg --import ``` ### Confirm Sun’s PGP public key is legit using its fingerprint ```console $ gpg --fingerprint hello@sunknudsen.com gpg: checking the trustdb gpg: marginals needed: 3 completes needed: 1 trust model: pgp gpg: depth: 0 valid: 1 signed: 0 trust: 0-, 0q, 0n, 0m, 0f, 1u pub rsa4096 2019-10-17 [C] C4FB DDC1 6A26 2672 920D 0A0F C132 3A37 7DE1 4C8B uid [ unknown] Sun Knudsen sub rsa4096 2019-10-17 [A] [expires: 2020-10-16] sub rsa4096 2019-10-17 [E] [expires: 2020-10-16] sub rsa4096 2019-10-17 [S] [expires: 2020-10-16] ``` See https://sunknudsen.com/, https://github.com/sunknudsen/pgp-public-key and https://www.youtube.com/sunknudsen/about and make sure fingerprint `C4FB DDC1 6A26 2672 920D 0A0F C132 3A37 7DE1 4C8B` matches the one published. 👍 ### Paste, encrypt and sign message (enter line break and use command `ctrl+d` to quit edit mode) ```console $ gpg --encrypt --sign --armor --output ~/Desktop/encrypted.asc -r john@example.net -r hello@sunknudsen.com gpg: 5574F4B0B0F67D7F: There is no assurance this key belongs to the named user sub rsa4096/5574F4B0B0F67D7F 2019-10-17 Sun Knudsen Primary key fingerprint: C4FB DDC1 6A26 2672 920D 0A0F C132 3A37 7DE1 4C8B Subkey fingerprint: 35A2 7551 E77C 3ED9 8527 032A 5574 F4B0 B0F6 7D7F It is NOT certain that the key belongs to the person named in the user ID. If you *really* know what you are doing, you may answer the next question with yes. Use this key anyway? (y/N) y This is a test! ``` ### Decrypt message to stdout and decode quoted-printable characters ```console $ gpg --decrypt ~/Desktop/encrypted.asc | perl -MMIME::QuotedPrint -0777 -nle 'print decode_qp($_)' gpg: encrypted with 4096-bit RSA key, ID 5574F4B0B0F67D7F, created 2019-10-17 "Sun Knudsen " gpg: encrypted with 4096-bit RSA key, ID 0DA22A1AC7DBA3F9, created 2020-06-16 "John Doe " gpg: Signature made Thu 18 Jun 10:45:04 2020 EDT gpg: using RSA key F365EDCF06F4D9F09BB7D4EB1BDC94DFB97BE4D4 gpg: Good signature from "John Doe " [ultimate] This is a test! ``` ### Clear passphrase from GnuPG cache ```shell gpg-connect-agent reloadagent /bye ```