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diff --git a/blog/2022-07-14-gnupg.org b/blog/2022-07-14-gnupg.org deleted file mode 100644 index 66aee7c..0000000 --- a/blog/2022-07-14-gnupg.org +++ /dev/null @@ -1,328 +0,0 @@ -#+title: GNU Privacy Guard (GPG) -#+date: 2022-07-14 - -** The History of GPG -:PROPERTIES: -:CUSTOM_ID: the-history-of-gpg -:END: -[[https://gnupg.org/][GNU Privacy Guard]], 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 -[[https://www.rfc-editor.org/rfc/rfc4880][RFC 4880]]. - -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 -[[https://en.wikipedia.org/wiki/Werner_Koch][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 -:PROPERTIES: -:CUSTOM_ID: encryption-algorithms -:END: -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: - -#+begin_src 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) -#+end_src - -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: - -- [[/blog/aes-encryption/][AES Encryption]] (2018) -- [[/blog/cryptography-basics/][Cryptography Basics]] (2020) - -*** Vulnerabilities -:PROPERTIES: -:CUSTOM_ID: vulnerabilities -:END: -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." ([[https://www.di.ens.fr/~pnguyen/pub_Ng04.htm][Source]]) -- GPG versions prior to 1.4.2.1 contain a false positive signature - verification bug. - ([[https://lists.gnupg.%20org/pipermail/gnupg-announce/2006q1/000211.html][Source]]) -- GPG versions prior to 1.4.2.2 cannot detect injection of unsigned - data. ( - [[https://lists.gnupg.org/pipermail/gnupg-announce/2006q1/000218.html][Source]]) -- 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. ([[https://lwn.net/Articles/727179/][Source]]) -- The [[https://en.wikipedia.org/wiki/ROCA_vulnerability][ROCA - Vulnerability]] affects RSA keys generated by YubiKey 4 tokens. - ([[https://crocs.fi.%20muni.cz/_media/public/papers/nemec_roca_ccs17_preprint.pdf][Source]]) -- The [[https://en.wikipedia.org/wiki/SigSpoof][SigSpoof Attack]] allows - an attacker to spoof digital signatures. - ([[https://arstechnica.%20com/information-technology/2018/06/decades-old-pgp-bug-allowed-hackers-to-spoof-just-about-anyones-signature/][Source]]) -- Libgcrypt 1.9.0 contains a severe flaw related to a heap buffer - overflow, fixed in Libgcrypt 1.9.1 - ([[https://web.archive.%20org/web/20210221012505/https://www.theregister.com/2021/01/29/severe_libgcrypt_bug/][Source]]) - -** Platforms -:PROPERTIES: -:CUSTOM_ID: platforms -:END: -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: - -- [[https://gnupg.org][GnuPG]] for Linux (depending on distro) -- [[https://gpg4win.org][Gpg4win]] for Windows -- [[https://gpgtools.org][GPGTools]] for macOS - -** Creating a Key Pair -:PROPERTIES: -:CUSTOM_ID: creating-a-key-pair -:END: -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: - -#+begin_src sh -sudo dnf install gpg -#+end_src - -Once installed, a user can create a new key pair with the following -command(s): - -#+begin_src sh -gpg --full-generate-key -#+end_src - -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: - -#+begin_src 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] -#+end_src - -Please note that GUI apps may differ slightly from the GPG command-line -interface. - -** Common Usage -:PROPERTIES: -:CUSTOM_ID: common-usage -:END: -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 -:PROPERTIES: -:CUSTOM_ID: email -:END: -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 -:PROPERTIES: -:CUSTOM_ID: file-encryption -:END: -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: - -#+begin_src sh -gpg --encrypt --output example_file.txt.gpg --recipient \ -recipient@example.com example_file.txt -#+end_src - -Once received, the recipient can decrypt the file with the following -command: - -#+begin_src sh -gpg --decrypt --output example_file.txt example_file.txt.gpg -#+end_src - -*** Ownership Signatures -:PROPERTIES: -:CUSTOM_ID: ownership-signatures -:END: -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 [[https://git-scm.com][Git]], the developer -simply needs to alter the =git commit= command to include the =-S= flag. -Here's an example: - -#+begin_src sh -git commit -S -m "my commit message" -#+end_src - -As an expansion of the example above, Git users can configure their -environment with a default key to use by adding their GPG signature: - -#+begin_src sh -git config --global user.signingkey XXXXXXXXXXXXXXXX -#+end_src - -If you're not sure what your signature is, you can find it titled =sig= -in the output of this command: - -#+begin_src sh -gpg --list-signatures -#+end_src - -*** File Integrity -:PROPERTIES: -:CUSTOM_ID: file-integrity -:END: -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: - -#+begin_src 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] -#+end_src - -** Finding Public Keys -:PROPERTIES: -:CUSTOM_ID: finding-public-keys -:END: -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: - -- [[https://pgp.mit.edu][pgp.mit.edu]] -- [[https://keys.openpgp.org][keys.openpgp.org]] |