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diff --git a/content/blog/2022-07-14-gnupg.md b/content/blog/2022-07-14-gnupg.md deleted file mode 100644 index 5be27a6..0000000 --- a/content/blog/2022-07-14-gnupg.md +++ /dev/null @@ -1,300 +0,0 @@ -+++ -date = 2022-07-14 -title = "GNU Privacy Guard (GPG)" -description = "" -draft = false -+++ - -# The History of GPG - -[GNU Privacy Guard](https://gnupg.org/), also known as GnuPG and GPG, is a free -("free" as in both speech and beer) software that fully implements the OpenPGP -Message Format documented in [RFC 4880](https://www.rfc-editor.org/rfc/rfc4880). - -I won't go in-depth on the full history of the software in this post, but it is -important to understand that GPG is not the same as PGP (Pretty Good Privacy), -which is a different implementation of RFC 4880. However, GPG was designed to -interoperate with PGP. - -GPG was originally developed in the late 1990s by [Werner -Koch](https://en.wikipedia.org/wiki/Werner_Koch) and has historically been -funded generously by the German government. - -Now that we have all the high-level info out of the way, let's dive into the -different aspects of GPG and its uses. - -# Encryption Algorithms - -GPG supports a wide range of different encryption algorithms, including -public-key, cipher, hash, and compression algorithms. The support for these -algorithms has grown since the adoption of the Libgcrypt library in the 2.x -versions of GPG. - -As you will be able to see below in an example of a full key generation with the -GPG command line tool, GPG recommends the following algorithms to new users: - -```sh -Please select what kind of key you want: - (1) RSA and RSA - (2) DSA and Elgamal - (3) DSA (sign only) - (4) RSA (sign only) - (9) ECC (sign and encrypt) *default* - (10) ECC (sign only) -``` - -I am not doing an in-depth explanation here in order to keep the focus on GPG -and not encryption algorithms. If you want a deep dive into cryptography or -encryption algorithms, please read my other posts: - -- [AES Encryption](../aes-encryption/) (2018) -- [Cryptography Basics](../cryptography-basics/) (2020) - -## Vulnerabilities - -As of 2022-07-14, there are a few different vulnerabilities associated with GPG -or the libraries it uses: - -- GPG versions 1.0.2--1.2.3 contains a bug where "as soon as one - (GPG-generated) ElGamal signature of an arbitrary message is released, one - can recover the signer's private key in less than a second on a PC." - ([Source](https://www.di.ens.fr/~pnguyen/pub_Ng04.htm)) -- GPG versions prior to 1.4.2.1 contain a false positive signature - verification bug. - ([Source](https://lists.gnupg.org/pipermail/gnupg-announce/2006q1/000211.html)) -- GPG versions prior to 1.4.2.2 cannot detect injection of unsigned data. ( - [Source](https://lists.gnupg.org/pipermail/gnupg-announce/2006q1/000218.html)) -- Libgcrypt, a library used by GPG, contained a bug which enabled full key - recovery for RSA-1024 and some RSA-2048 keys. This was resolved in a GPG - update in 2017. ([Source](https://lwn.net/Articles/727179/)) -- The [ROCA Vulnerability](https://en.wikipedia.org/wiki/ROCA_vulnerability) - affects RSA keys generated by YubiKey 4 tokens. - ([Source](https://crocs.fi.muni.cz/_media/public/papers/nemec_roca_ccs17_preprint.pdf)) -- The [SigSpoof Attack](https://en.wikipedia.org/wiki/SigSpoof) allows an - attacker to spoof digital signatures. - ([Source](https://arstechnica.com/information-technology/2018/06/decades-old-pgp-bug-allowed-hackers-to-spoof-just-about-anyones-signature/)) -- Libgcrypt 1.9.0 contains a severe flaw related to a heap buffer overflow, - fixed in Libgcrypt 1.9.1 - ([Source](https://web.archive.org/web/20210221012505/https://www.theregister.com/2021/01/29/severe_libgcrypt_bug/)) - -### Platforms - -Originally developed as a command-line program for \*nix systems, GPG now has a -wealth of front-end applications and libraries available for end-users. However, -the most recommended programs remain the same: - -- [GnuPG](https://gnupg.org) for Linux (depending on distro) -- [Gpg4win](https://gpg4win.org) for Windows -- [GPGTools](https://gpgtools.org) for macOS - -# Creating a Key Pair - -In order to create a GPG key pair, a user would first need to install GPG on -their system. If we're assuming that the user is on Fedora Linux, they would -execute the following: - -```sh -sudo dnf install gpg -``` - -Once installed, a user can create a new key pair with the following command(s): - -```sh -gpg --full-generate-key -``` - -GPG will walk the user through an interactive setup that asks for an algorithm -preference, expiration date, name, and email to associate with this key. - -See the following example key set-up for a default key generation using the -GnuPG command-line interface: - -```sh -gpg (GnuPG) 2.3.6; Copyright (C) 2021 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. - -Please select what kind of key you want: - (1) RSA and RSA - (2) DSA and Elgamal - (3) DSA (sign only) - (4) RSA (sign only) - (9) ECC (sign and encrypt) *default* - (10) ECC (sign only) - (14) Existing key from card -Your selection? 9 -Please select which elliptic curve you want: - (1) Curve 25519 *default* - (4) NIST P-384 -Your selection? 1 -Please specify how long the key should be valid. - 0 = key does not expire - <n> = key expires in n days - <n>w = key expires in n weeks - <n>m = key expires in n months - <n>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: johndoe@example.com -Comment: test key -You selected this USER-ID: - "John Doe (test key) <johndoe@example.com>" - -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: revocation certificate stored as 'example.rev' -public and secret key created and signed. - -pub ed25519 2022-07-14 [SC] - E955B7700FFC11EF51C2BA1FE096AACDD4C32E9C -uid John Doe (test key) <johndoe@example.com> -sub cv25519 2022-07-14 [E] -``` - -Please note that GUI apps may differ slightly from the GPG command-line -interface. - -# Common Usage - -As noted in RFC 4880, the general functions of OpenPGP are as follows: - -- digital signatures -- encryption -- compression -- Radix-64 conversion -- key management and certificate services - -From this, you can probably gather that the main use of GPG is for encrypting -data and/or signing the data with a key. The purpose of encrypting data with GPG -is to ensure that no one except the intended recipient(s) can access the data. - -Let's explore some specific GPG use-cases. - -## Email - -One of the more popular uses of GPG is to sign and/or encrypt emails. With the -use of a GPG keypair, you can encrypt a message, its subject, and even the -attachments within. - -The first process, regarding the signing of a message without any encryption, is -generally used to provide assurance that an email is truly coming from the -sender that the message claims. When I send an email, and it's signed with my -public key, the recipient(s) of the message can verify that the message was -signed with my personal key. - -The second process, regarding the actual encryption of the message and its -contents, works by using a combination of the sender's keys and the recipient's -keys. This process may vary slightly by implementation, but it most commonly -uses asymmetric cryptography, also known as public-key cryptography. In this -version of encryption, the sender's private key to sign the message and a -combination of the sender's keys and the recipient's public key to encrypt the -message. - -If two people each have their own private keys and exchange their public keys, -they can send encrypted messages back and forth with GPG. This is also possible -with symmetric cryptography, but the process differs since there are no key -pairs. - -Implementation of email encryption varies greatly between email clients, so you -will need to reference your email client's documentation to ensure you are -setting it up correctly for that specific client. - -## File Encryption - -As noted in the section above regarding emails, GPG enables users to be able to -send a message to each other if they are both set-up with GPG keys. In this -example, I am going to show how a user could send a file called -`example_file.txt` to another user via the recipient's email. - -The sender would find the file they want to send and execute the following -command: - -```sh -gpg --encrypt --output example_file.txt.gpg --recipient \ -recipient@example.com example_file.txt -``` - -Once received, the recipient can decrypt the file with the following command: - -```sh -gpg --decrypt --output example_file.txt example_file.txt.gpg -``` - -## Ownership Signatures - -One important aspect of GPG, especially for developers, is the ability to sign -data without encrypting it. For example, developers often sign code changes when -they commit the changes back to a central repository, in order to display -ownership of who made the changes. This allows other users to look at a code -change and determine that the change was valid. - -In order to do this using [Git](https://git-scm.com), the developer simply needs -to alter the `git commit` command to include the `-S` flag. Here's an example: - -```sh -git commit -S -m "my commit message" -``` - -As an expansion of the example above, Git users can configure their environment -with a default key to use by adding their GPG signature: - -```sh -git config --global user.signingkey XXXXXXXXXXXXXXXX -``` - -If you're not sure what your signature is, you can find it titled `sig` in the -output of this command: - -```sh -gpg --list-signatures -``` - -## File Integrity - -When a person generates a signature for data, they are allowing users the -ability to verify the signature on that data in the future to ensure the data -has not been corrupted. This is most common with software applications hosted on -the internet - developers provide signatures so that users can verify a website -was not hijacked and download links replaced with dangerous software. - -In order to verify signed data, a user needs to have: - -1. The signed data -2. A signature file -3. The public GPG key of the signer - -Once the signer's public key is imported on the user's system, and they have the -data and signature, they can verify the data with the following commands: - -```sh -# If the signature is attached to the data -gpg --verify [signature-file] - -# If the signature is detached as a separate file from the data -gpg --verify [signature-file] [original-file] -``` - -### Finding Public Keys - -In order to use GPG with others, a user needs to know the other user(s) keys. -This is easy to do if the user knows the other user(s) in person, but may be -hard if the relationship is strictly digital. Luckily, there are a few options. -The first option is to look at a user's web page or social pages if they have -them. - -Otherwise, the best option is to use a keyserver, such as: - -- [pgp.mit.edu](https://pgp.mit.edu) -- [keys.openpgp.org](https://keys.openpgp.org) |