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How do you know who to trust? How do you know they are who they say they are? Your goal in this project is to learn about public key cryptography, gpg, verifying identities, and the web of trust. You will need to:
You should read the entire assignment before getting started. You may wish to think about a strategy that will help you convince others to sign your fake key or to sign their valid key with your fake key.
Important: Do not upload either of your keys to any public keyserver. It would be unethical for this class assignment to pollute the information on these public resources. We will search the keyservers for your public keys, and if we find them, you will receive zero points. If you upload your key to a public key server by accident, you must contact the instructor immediately.
This assignment has two due dates:
Acknowledgements: This assignment was based, with permission, on this one by William Enck, who derived his (with permission) from an assignment created by Adam Doupé.
Any changes to this page will be put here for easy reference. Typo fixes and minor clarifications are not listed here.
other and sanity_check dictionaries. If you downloaded the previous version, then: change the number 30 in the sanity_checks dictionary to 15 (4 occurrences), and add the 2nd to last field in the new version in the other dictionary.You will need to install GPG, the Gnu Privacy Guard – this is an RSA client for encrypting emails. Installation packages can be found toward the bottom of this page; there are GUI versions for the major operating systems. If GPG is already installed with your email client, that’s fine – you don’t need to install it again. It is also installed on the course Docker image, but you may not want to use the command-line version.
You MUST create a 4096 bit RSA key! This is what the adversarial key will be (see below for that), and if yours is different (3072 bits, for example), then it will be easy to differentiate them.
Create a public/private GPG keypair specifically for this project with the following requirements:
Other students will need to verify your identity, so the name and email must be exact. This will be automatically checked by GradeScope in Part 2, so for the purposes of this assignment, your name is what GradeScope thinks your name is.
There are many guides for creating a GPG keypair, including information in the man page for the command. I recommend GitHub’s guide for generating a new GPG key.
Important note for existing GPG users: If your existing key is with your formal UVA email address (mst3k@virginia.edu), then you should NOT use that one, and creating a second key with the same exact email address causes problems. You should add +nws to the end of your userid as such: mst3k+nws@virginia.edu. Note that you can, in general, add anything after your username and a +; we are just going to use +nws for this assignment.
I cannot stress this enough, due to the nature of the assignment, we cannot and will not sign multiple keys for you. This may result in you getting a zero on the assignment. Backup your keypair. Because the keypair is being used for only this assignment, it is not as critical to keep it safe as if it were your normal RSA key – thus, you can just email the keys (both public and private) to yourself. If you lose the key once you’ve uploaded it to the server, then you will not be able to finish the assignment. Every UVA student has storage in Box, and you can use that as well – or any other mechanism to backup your keypair (including your secret key). Once your key is generated, backup your public and private key. Seriously, you’ve been warned.
Save your public key as a file called mst3k.gpg, where mst3k is your userid, and then upload your public key to GradeScope to the assignment “Web of Trust Upload”. The server will then check to see if your public key is valid, and only if it is, the server will sign your public key with the course’s keypair, which has a fingerprint of FDA0 7EF5 8A87 1F57 9D6D 56DA 23AD 0D8A 73E5 7217. You should download this key, verify the fingerprint, and import it into your GPG keyring.
The server will also generate an adversarial keypair with a random name of another student in the class and the same email as your key. You will be able to download this adversarial keypair (both the public and private key).
As this is signing your key, you may only upload your key ONCE. The system will not sign a second keypair for you, as that means you lost your original keypair. Note that a failed submission (wrong files submitted, incorrect format, etc.) will not count as the one time upload.
This part, along with the next part, are due by the earlier due date.
You need to send an RSA encrypted email to the course email address, which is listed on the Canvas landing page. In it, you should request your secret code. Include some witty or interesting quote. Both the request and the quote should be encrypted via GPG and the course’s keypair.
Note: If you have the ability to choose the file name of the encrypted file, such as if you are doing it as an attachment, please name it mst3k.txt.gpg. If you don’t have the option to name it (it’s cut-and-pasted), that’s fine.
You need to send this email by the earlier due date (one week before the later due date).
You will receive a response back with a code specific to your userid; this code will need to be included in the weboftrust.py (src) file that you submit. Note that this will take us some time to respond! There are a lot of students in the class. However, as long as you sent your email by the earlier due date, you will receive your response no later that 24 hours before the later due date.
This part (just the sending of the email), and the previous part (uploading your key), are due by the earlier due date.
Here’s where the fun starts. You need to get your key signed by at least 15 of your fellow students’ public keys. The signatures must be from a valid key in this class: How will you know?
Note: For the purposes of this assignment, a “valid” key is a key created by one of your classmates and signed by the class signing key. The adversarial keys created by GradeScope are not “valid” keys. Signatures from invalid keys do not count toward the 15 total
There are lots of resources on the Internet that describe signing public keys. Here are two that focus on the command line versions:
That being said, the GUIs for GPG are pretty easy to use, and you probably can figure out how to sign a key by tinkering around.
Using what you learned from the above, you must sign at least 15 of your fellow students’ public keys. You are encourage to sign more, but only public keys valid for this class count: How will you know?
A big part of this assignment is figuring out how to determine if the key you are signing is actually the correct key for the person you think it is.
Note: We will only count signatures from your valid key on other students’ valid keys. That is, signing other students’ valid keys with your adversarial key will not count towards your required number if signatures. Similarly, signing someone else’s adversarial key with your valid key will not count toward your required number of signatures.
Note: The goal of this assignment is to (1) have you send and receive a PGP encrypted email, and (2) get a feel for how hard it is to know who and what to trust. The goal is not to have you feel annoyed or angry at your fellow students if you end up being fooled. So the deductions for that are going to be quite small. I want people to come away from this assignment having learned something, uncomfortable though it may be to learn how hard it is to know who to trust. Having you come away bitter and angry at myself, this assignment, or your fellow students does not help achieve that goal. So don’t stress to much about the point deductions.
Note that signing one of your keys (either one) with your other key will not affect your grade. Also note that signing one or two invalid keys with your own will not sink your grade!
The exact amount of points will be determined at the end, once we see the results. This is for both the deductions and the extra credit bonus.
There are TWO submissions for this assignment, with different due dates; the second one is due a week after the first one.
The first is to the “Web of Trust Upload” assignment in Gradescope, which is where you upload your key created in part 1, and this submission is described in part 2. The file should be named mst3k.pub, where mst3k is your UVA userid. You also have to send the GPG encrypted email to the course email address.
The second is to the “Web of Trust Submission” assignment in Gradescope, where you are submitting your public key (with the 15 signatures), which you will need to export into a mst3k.pub file.
You will also need to submit an edited version of weboftrust.py (src); that file explains what to fill in and where.