There are a lot of random topics I’ve wanted to write about since I started Dhole Moments, and for one reason or another, haven’t actually written about. I know from past experience with other projects that if you don’t occasionally do some housekeeping, your backlog eventually collapses under its own gravity and you can never escape from it.
So, to prevent that, I’d like to periodically take some time to clean up some of those loose ends that collect over time.
Random-Access AEAD
AEAD stands for Authenticated Encryption with Associated Data. Typically, AEAD constructions involve a stream cipher (which may also be a block cipher in counter mode) and a message authentication code (which may also be an almost-universal hash function).
AEAD modes are designed for one-shot APIs: Encrypt (then authenticate) all at once; (verify then) decrypt all at once. AES-GCM, ChaPoly, etc.
AEADs are less great at providing random access to the underlying plaintext. For example: If you’re encrypting a 240 GB file with AES-GCM, but you only need a 512 KB chunk at some arbitrary point in the file, you’re forced to choose between either:
- Authenticating the rest of the AES-GCM ciphertext, then decrypting only the relevant chunk. (Performance sucks.)
- Sacrificing integrity and decrypting the desired chunk with AES-CTR.
Being forced to choose between speed and security will almost certainly result in a loss of security. The incentives of software developers (especially with fly-by-night startup engineers) all-but-guarantee this outcome.
Consequently, there have been several implementations of streaming-friendly AEAD. The most famous of which is Phil Rogaway’s STREAM construction.
Source: Rogaway’s paper
The downside to STREAM is that it requires an additional T bytes (e.g. 16 for an 128-bit authentication tag) for each chunk of the plaintext.
A similar solution, as implemented in the AWS Encryption SDK, is to carefully separate plaintexts into equal-sized frames and have special rules governing IV/nonce selection. This lets you facilitate random access while still making the security of the whole system easy to reason about.
Can we do better than STREAM and message framing?
The most straightforward idea is to use a Merkle tree on the ciphertext with a stream cipher for extracting a distinct key for each leaf node. This can be applied to existing AEAD ciphertexts, out of band, to create a sort of deep authentication tag that can be used to authenticate any random subset of the message (provided you have the correct nonce/key).
However, I haven’t found the time to develop this idea into something that can be toyed with by myself and other researchers.
More Introductory Articles
Let’s face it:
Art by Riley
I’ve previously suggested an alternative strategy for programmers to learn cryptography. I’d like to do more posts covering introductory material for the topics I’m familiar with, so anyone who wants to actually employ my proposed strategy can carry themselves across the finish line.
Dissecting Dog-Whistles
Random fact: My fursona is a dhole–also known as a whistling dog.
Soatok is a dhole, not a fox. Art by Khia.
Coincidentally, I’m deeply fascinated by language, and planned to start a series analyzing dog-whistle language (especially the kind commonly used against queer subcultures).
However, the very nature of dog-whistle language provides a veneer of plausible deniability for the whistler’s intent, which makes it very difficult to address them in a meaningful way that doesn’t undermine your own credibility.
So, for the time being, this is on the back-burner.
Reader Questions
I’ve received quite a few questions via email and social media since I started this blog in April. The most obvious thing to do with these questions would be to periodically collate a bunch of them into a Questions and Answer style post.
However! I have an open source projected called FAQ Off that is way more efficient at the Q&A format than a long-form blog post. If you’d like to see it in action, start here.
Art by Kyume
General Punditry
I make a lot of dumb jokes, typically involving puns and other wordplay. Most of these live in private Telegram conversations with other furries, but a few have leaked out onto Twitter over the years.
Is automated vulnerability scanning a nessusity?— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) November 23, 2017
Nurse: "I suspect this patient attempted to shove a foreign object into their urethra for pleasure"
Doctor: "I believe your theory is sound"
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) June 25, 2018
A lot of them involve queer lingo.
People say it's lonely at the top.No wonder there's so many bottoms in this fandom 😛
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) December 30, 2019
BitTorrent users are thirsty bottoms. Always complaining about wanting more seed.
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) August 4, 2019
My RAID controller has big disk synergy
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) August 1, 2018
Some of them involve furry in-jokes.
Q) Why are foxes so prevalent in the furry fandom?A) We're a sub-culture not a dom-culture.
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) May 24, 2018
Intrusion detection systems are old hat. What we need is a protrusion detection system.
Introducing OwO
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) February 1, 2018
Some are just silly.
Using mined bitcoins to buy a pumpkin spice latte makes you an ASIC bitch, right?— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) February 6, 2018
So in gay male furry culture if you give into a booty call from your ex-boyfriend… does that mean you were craving the XD?
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) August 25, 2018
If SQL is pronounced "sequel" then PHP must be pronounced "fap".
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) July 23, 2019
What do you call a submissive dragon with a mathematics background who's already lubed up for you?
A sliding scale.
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) December 26, 2018
Did you hear about the clairvoyant babyfur that broke RSA?
Turns out, all you needed was a padding oracle.
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) October 1, 2017
I should look for my next partner in a nuclear chemistry lab.
I hear they're good at dating.
— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) December 8, 2016
In my humble opinion, there haven’t been nearly enough puns on this blog (unless the embedded tweets above count).
Normally, this is where I’d proclaim, “I shall rectify this mistake” and proceed to make an ass out of myself, but I don’t like forced and obvious puns.
A lot of furries get this wrong: “Pawesome” is not clever, unless you’re talking to someone with a marsupial fursona. Then maybe.
The best puns come in two forms: They’re either so clever that you never saw it coming, or they’re just clever enough that the punchline lands at the same time you realized a bad pun was even possible.
Only Soatok brand puns are 100% whole groan— Mastodon: soatok@furry.engineer, Cohost: soatok (@SoatokDhole) January 26, 2018
Miscellaneous / Meta
The past few blog posts touched a little on political subjects (especially How and Why America Was Hit So Hard By COVID-19, but this short-term trend actually started with my Pride Month post).
At some point in the future, I may write a post dedicated to politics, but for the time being, it’s not really a subject I care enough about in and of itself to emphasize all the time.
Let me be clear: Being gay in America is inherently political. Developing technology is inherently political (although you don’t always realize it). Being a gay technologist, saying something politically significant is an inevitability.
But I’m not interested in the traditional roles and narratives that infect politics and political discourse. Labels are stupid and I’m not interested in being a Useful Idiot for anyone’s propaganda.
The most difficult thing about writing blog posts for me is coming up with a meaningful title. I’ve lost many hours due to the writer’s block that ensues.
The second most difficult thing for me is writing closing statements that aren’t totally redundant.
https://www.youtube.com/embed/l44OV2jlN7A?start=665&feature=oembed
George Carlin – “Count the Superfluous Redundant Pleonastic Tautologies” – Skip to 11:05 if WordPress breaks something
Some bloggers like to sign off like they’re writing an email. “Happy hacking!” and whatnot. To me, this feels forced and inauthentic, like a bad pun.
So instead, here’s a totally sick piece of art I got from @MrJimmyDaFloof.
Furry artists are, like the rest of the fandom, amazing.
https://soatok.blog/2020/07/07/dont-forget-to-brush-your-fur/
If you’re reading this wondering if you should stop using AES-GCM in some standard protocol (TLS 1.3), the short answer is “No, you’re fine”.I specialize in secure implementations of cryptography, and my years of experience in this field have led me to dislike AES-GCM.
This post is about why I dislike AES-GCM’s design, not “why AES-GCM is insecure and should be avoided”. AES-GCM is still miles above what most developers reach for when they want to encrypt (e.g. ECB mode or CBC mode). If you want a detailed comparison, read this.
To be clear: This is solely my opinion and not representative of any company or academic institution.
What is AES-GCM?
AES-GCM is an authenticated encryption mode that uses the AES block cipher in counter mode with a polynomial MAC based on Galois field multiplication.In order to explain why AES-GCM sucks, I have to first explain what I dislike about the AES block cipher. Then, I can describe why I’m filled with sadness every time I see the AES-GCM construction used.
What is AES?
The Advanced Encryption Standard (AES) is a specific subset of a block cipher called Rijndael.Rijndael’s design is based on a substitution-permutation network, which broke tradition from many block ciphers of its era (including its predecessor, DES) in not using a Feistel network.
AES only includes three flavors of Rijndael: AES-128, AES-192, and AES-256. The difference between these flavors is the size of the key and the number of rounds used, but–and this is often overlooked–not the block size.
As a block cipher, AES always operates on 128-bit (16 byte) blocks of plaintext, regardless of the key size.
This is generally considered acceptable because AES is a secure pseudorandom permutation (PRP), which means that every possible plaintext block maps directly to one ciphertext block, and thus birthday collisions are not possible. (A pseudorandom function (PRF), conversely, does have birthday bound problems.)
Why AES Sucks
Art by Khia.Side-Channels
The biggest reason why AES sucks is that its design uses a lookup table (called an S-Box) indexed by secret data, which is inherently vulnerable to cache-timing attacks (PDF).There are workarounds for this AES vulnerability, but they either require hardware acceleration (AES-NI) or a technique called bitslicing.
The short of it is: With AES, you’re either using hardware acceleration, or you have to choose between performance and security. You cannot get fast, constant-time AES without hardware support.
Block Size
AES-128 is considered by experts to have a security level of 128 bits.Similarly, AES-192 gets certified at 192-bit security, and AES-256 gets 256-bit security.
However, the AES block size is only 128 bits!
That might not sound like a big deal, but it severely limits the constructions you can create out of AES.
Consider the case of AES-CBC, where the output of each block of encryption is combined with the next block of plaintext (using XOR). This is typically used with a random 128-bit block (called the initialization vector, or IV) for the first block.
This means you expect a collision after encrypting (at 50% probability) blocks.
When you start getting collisions, you can break CBC mode, as this video demonstrates:
https://www.youtube.com/watch?v=v0IsYNDMV7A
This is significantly smaller than the you expect from AES.
Post-Quantum Security?
With respect to the number of attempts needed to find the correct key, cryptographers estimate that AES-128 will have a post-quantum security level of 64 bits, AES-192 will have a post-quantum security level of 96 bits, and AES-256 will have a post-quantum security level of 128 bits.This is because Grover’s quantum search algorithm can search unsorted items in time, which can be used to reduce the total number of possible secrets from to . This effectively cuts the security level, expressed in bits, in half.
Note that this heuristic estimate is based on the number of guesses (a time factor), and doesn’t take circuit size into consideration. Grover’s algorithm also doesn’t parallelize well. The real-world security of AES may still be above 100 bits if you consider these nuances.
But remember, even AES-256 operates on 128-bit blocks.
Consequently, for AES-256, there should be approximately (plaintext, key) pairs that produce any given ciphertext block.
Furthermore, there will be many keys that, for a constant plaintext block, will produce the same ciphertext block despite being a different key entirely. (n.b. This doesn’t mean for all plaintext/ciphertext block pairings, just some arbitrary pairing.)
Concrete example: Encrypting a plaintext block consisting of sixteen NUL bytes will yield a specific 128-bit ciphertext exactly once for each given AES-128 key. However, there are times as many AES-256 keys as there are possible plaintext/ciphertexts. Keep this in mind for AES-GCM.
This means it’s conceivable to accidentally construct a protocol that, despite using AES-256 safely, has a post-quantum security level on par with AES-128, which is only 64 bits.
This would not be nearly as much of a problem if AES’s block size was 256 bits.
Real-World Example: Signal
The Signal messaging app is the state-of-the-art for private communications. If you were previously using PGP and email, you should use Signal instead.Signal aims to provide private communications (text messaging, voice calls) between two mobile devices, piggybacking on your pre-existing contacts list.
Part of their operational requirements is that they must be user-friendly and secure on a wide range of Android devices, stretching all the way back to Android 4.4.
The Signal Protocol uses AES-CBC + HMAC-SHA256 for message encryption. Each message is encrypted with a different AES key (due to the Double Ratchet), which limits the practical blast radius of a cache-timing attack and makes practical exploitation difficult (since you can’t effectively replay decryption in order to leak bits about the key).
Thus, Signal’s message encryption is still secure even in the presence of vulnerable AES implementations.
Hooray for well-engineered protocols managing to actually protect users.
Art by Swizz.However, the storage service in the Signal App uses AES-GCM, and this key has to be reused in order for the encrypted storage to operate.
This means, for older phones without dedicated hardware support for AES (i.e. low-priced phones from 2013, which Signal aims to support), the risk of cache-timing attacks is still present.
This is unacceptable!
What this means is, a malicious app that can flush the CPU cache and measure timing with sufficient precision can siphon the AES-GCM key used by Signal to encrypt your storage without ever violating the security boundaries enforced by the Android operating system.
As a result of the security boundaries never being crossed, these kind of side-channel attacks would likely evade forensic analysis, and would therefore be of interest to the malware developers working for nation states.
Of course, if you’re on newer hardware (i.e. Qualcomm Snapdragon 835), you have hardware-accelerated AES available, so it’s probably a moot point.
Why AES-GCM Sucks Even More
AES-GCM is an authenticated encryption mode that also supports additional authenticated data. Cryptographers call these modes AEAD.AEAD modes are more flexible than simple block ciphers. Generally, your encryption API accepts the following:
- The plaintext message.
- The encryption key.
- A nonce (: A number that must only be used once).
- Optional additional data which will be authenticated but not encrypted.
The output of an AEAD function is both the ciphertext and an authentication tag, which is necessary (along with the key and nonce, and optional additional data) to decrypt the plaintext.
Cryptographers almost universally recommend using AEAD modes for symmetric-key data encryption.
That being said, AES-GCM is possibly my least favorite AEAD, and I’ve got good reasons to dislike it beyond simply, “It uses AES”.
The deeper you look into AES-GCM’s design, the harder you will feel this sticker.
GHASH Brittleness
The way AES-GCM is initialized is stupid: You encrypt an all-zero block with your AES key (in ECB mode) and store it in a variable called . This value is used for authenticating all messages authenticated under that AES key, rather than for a given (key, nonce) pair.
Diagram describing Galois/Counter Mode, taken from Wikipedia.
This is often sold as an advantage: Reusing allows for better performance. However, it makes GCM brittle: Reusing a nonce allows an attacker to recover H and then forge messages forever. This is called the “forbidden attack”, and led to real world practical breaks.Let’s contrast AES-GCM with the other AEAD mode supported by TLS: ChaCha20-Poly1305, or ChaPoly for short.
ChaPoly uses one-time message authentication keys (derived from each key/nonce pair). If you manage to leak a Poly1305 key, the impact is limited to the messages encrypted under that (ChaCha20 key, nonce) pair.
While that’s still bad, it isn’t “decrypt all messages under that key forever” bad like with AES-GCM.
Note: “Message Authentication” here is symmetric, which only provides a property called message integrity, not sender authenticity. For the latter, you need asymmetric cryptography (wherein the ability to verify a message doesn’t imply the capability to generate a new signature), which is totally disparate from symmetric algorithms like AES or GHASH. You probably don’t need to care about this nuance right now, but it’s good to know in case you’re quizzed on it later.
H Reuse and Multi-User Security
If you recall, AES operates on 128-bit blocks even when 256-bit keys are used.If we assume AES is well-behaved, we can deduce that there are approximately different 256-bit keys that will map a single plaintext block to a single ciphertext block.
This is trivial to calculate. Simply divide the number of possible keys () by the number of possible block states () to yield the number of keys that produce a given ciphertext for a single block of plaintext: .
Each key that will map an arbitrarily specific plaintext block to a specific ciphertext block is also separated in the keyspace by approximately .
This means there are approximately independent keys that will map a given all-zero plaintext block to an arbitrarily chosen value of (if we assume AES doesn’t have weird biases).
Credit: Harubaki
“Why Does This Matter?”
It means that, with keys larger than 128 bits, you can model the selection of as a 128-bit pseudorandom function, rather than a 128-bit permutation. As a result, you an expect a collision with 50% probability after only different keys are selected.Note: Your 128-bit randomly generated AES keys already have this probability baked into their selection, but this specific analysis doesn’t really apply for 128-bit keys since AES is a PRP, not a PRF, so there is no “collision” risk. However, you end up at the same upper limit either way.
But 50% isn’t good enough for cryptographic security.
In most real-world systems, we target a collision risk. So that means our safety limit is actually different AES keys before you have to worry about reuse.
This isn’t the same thing as symmetric wear-out (where you need to re-key after a given number of encryptions to prevent nonce reuse). Rather, it means after your entire population has exhausted the safety limit of different AES keys, you have to either accept the risk or stop using AES-GCM.
If you have a billion users (), the safety limit is breached after AES keys per user (approximately 262,000).
“What Good is H Reuse for Attackers if HF differs?”
There are two numbers used in AES-GCM that are derived from the AES key. is used for block multiplication, and (the value of with a counter of 0 from the following diagram) is XORed with the final result to produce the authentication tag.The arrow highlighted with green is HF.
It’s tempting to think that a reuse of isn’t a concern because will necessarily be randomized, which prevents an attacker from observing when collides. It’s certainly true that the single-block collision risk discussed previously for will almost certainly not also result in a collision for . And since isn’t reused unless a nonce is reused (which also leaks directly), this might seem like a non-issue.
Art by Khia.
However, it’s straightforward to go from a condition of reuse to an adaptive chosen-ciphertext attack.
- Intercept multiple valid ciphertexts.
- e.g. Multiple JWTs encrypted with
{"alg":"A256GCM"}
- Use your knowledge of , the ciphertext, and the AAD to calculate the GCM tag up to the final XOR. This, along with the existing authentication tag, will tell you the value of for a given nonce.
- Calculate a new authentication tag for a chosen ciphertext using and your candidate value, then replay it into the target system.
While the blinding offered by XORing the final output with is sufficient to stop from being leaked directly, the protection is one-way.
Ergo, a collision in is not sufficiently thwarted by .
“How Could the Designers Have Prevented This?”
The core issue here is the AES block size, again.If we were analyzing a 256-bit block variant of AES, and a congruent GCM construction built atop it, none of what I wrote in this section would apply.
However, the 128-bit block size was a design constraint enforced by NIST in the AES competition. This block size was during an era of 64-bit block ciphers (e.g. Triple-DES and Blowfish), so it was a significant improvement at the time.
NIST’s AES competition also inherited from the US government’s tradition of thinking in terms of “security levels”, which is why there are three different permitted key sizes (128, 192, or 256 bits).
“Why Isn’t This a Vulnerability?”
There’s always a significant gap in security, wherein something isn’t safe to recommend, but also isn’t susceptible to a known practical attack. This gap is important to keep systems secure, even when they aren’t on the bleeding edge of security.Using 1024-bit RSA is a good example of this: No one has yet, to my knowledge, successfully factored a 1024-bit RSA public key. However, most systems have recommended a minimum 2048-bit for years (and many recommend 3072-bit or 4096-bit today).
With AES-GCM, the expected distance between collisions in is , and finding an untargeted collision requires being able to observe more than different sessions, and somehow distinguish when collides.
As a user, you know that after different keys, you’ve crossed the safety boundary for avoiding collisions. But as an attacker, you need bites at the apple, not . Additionally, you need some sort of oracle or distinguisher for when this happens.
We don’t have that kind of distinguisher available to us today. And even if we had one available, the amount of data you need to search in order for any two users in the population to reuse/collide is challenging to work with. You would need the computational and data storages of a major cloud service provider to even think about pulling the attack off.
Naturally, this isn’t a practical vulnerability. This is just another gripe I have with AES-GCM, as someone who has to work with cryptographic algorithms a lot.
Short Nonces
Although the AES block size is 16 bytes, AES-GCM nonces are only 12 bytes. The latter 4 bytes are dedicated to an internal counter, which is used with AES in Counter Mode to actually encrypt/decrypt messages.(Yes, you can use arbitrary length nonces with AES-GCM, but if you use nonces longer than 12 bytes, they get hashed into 12 bytes anyway, so it’s not a detail most people should concern themselves with.)
If you ask a cryptographer, “How much can I encrypt safely with AES-GCM?” you’ll get two different answers.
- Message Length Limit: AES-GCM can be used to encrypt messages up to bytes long, under a given (key, nonce) pair.
- Number of Messages Limit: If you generate your nonces randomly, you have a 50% chance of a nonce collision after messages.
However, 50% isn’t conservative enough for most systems, so the safety margin is usually much lower. Cryptographers generally set the key wear-out of AES-GCM at random nonces, which represents a collision probability of one in 4 billion.These limits are acceptable for session keys for encryption-in-transit, but they impose serious operational limits on application-layer encryption with long-term keys.
Random Key Robustness
Before the advent of AEAD modes, cryptographers used to combine block cipher modes of operation (e.g. AES-CBC, AES-CTR) with a separate message authentication code algorithm (e.g. HMAC, CBC-MAC).You had to be careful in how you composed your protocol, lest you invite Cryptographic Doom into your life. A lot of developers screwed this up. Standardized AEAD modes promised to make life easier.
Many developers gained their intuition for authenticated encryption modes from protocols like Signal’s (which combines AES-CBC with HMAC-SHA256), and would expect AES-GCM to be a drop-in replacement.
Unfortunately, GMAC doesn’t offer the same security benefits as HMAC: Finding a different (ciphertext, HMAC key) pair that produces the same authentication tag is a hard problem, due to HMAC’s reliance on cryptographic hash functions. This makes HMAC-based constructions “message committing”, which instills Random Key Robustness.
Critically, AES-GCM doesn’t have this property. You can calculate a random (ciphertext, key) pair that collides with a given authentication tag very easily.
This fact prohibits AES-GCM from being considered for use with OPAQUE (which requires RKR), one of the upcoming password-authenticated key exchange algorithms. (Read more about them here.)
Better-Designed Algorithms
You might be thinking, “Okay random furry, if you hate AES-GCM so much, what would you propose we use instead?”I’m glad you asked!
XChaCha20-Poly1305
For encrypting messages under a long-term key, you can’t really beat XChaCha20-Poly1305.
- ChaCha is a stream cipher based on a 512-bit ARX hash function in counter mode. ChaCha doesn’t use S-Boxes. It’s fast and constant-time without hardware acceleration.
- ChaCha20 is ChaCha with 20 rounds.
- XChaCha nonces are 24 bytes, which allows you to generate them randomly and not worry about a birthday collision until about messages (for the same collision probability as AES-GCM).
- Poly1305 uses different 256-bit key for each (nonce, key) pair and is easier to implement in constant-time than AES-GCM.
- XChaCha20-Poly1305 uses the first 16 bytes of the nonce and the 256-bit key to generate a distinct subkey, and then employs the standard ChaCha20-Poly1305 construction used in TLS today.
For application-layer cryptography, XChaCha20-Poly1305 contains most of the properties you’d want from an authenticated mode.
However, like AES-GCM (and all other Polynomial MACs I’ve heard of), it is not message committing.
The Gimli Permutation
For lightweight cryptography (n.b. important for IoT), the Gimli permutation (e.g. employed in libhydrogen) is an attractive option.Gimli is a Round 2 candidate in NIST’s Lightweight Cryptography project. The Gimli permutation offers a lot of applications: a hash function, message authentication, encryption, etc.
Critically, it’s possible to construct a message-committing protocol out of Gimli that will hit a lot of the performance goals important to embedded systems.
Closing Remarks
Despite my personal disdain for AES-GCM, if you’re using it as intended by cryptographers, it’s good enough.Don’t throw AES-GCM out just because of my opinions. It’s very likely the best option you have.
Although I personally dislike AES and GCM, I’m still deeply appreciative of the brilliance and ingenuity that went into both designs.
My desire is for the industry to improve upon AES and GCM in future cipher designs so we can protect more people, from a wider range of threats, in more diverse protocols, at a cheaper CPU/memory/time cost.
We wouldn’t have a secure modern Internet without the work of Vincent Rijmen, Joan Daemen, John Viega, David A. McGrew, and the countless other cryptographers and security researchers who made AES-GCM possible.
Change Log
- 2021-10-26: Added section on H Reuse and Multi-User Security.
https://soatok.blog/2020/05/13/why-aes-gcm-sucks/
#AES #AESGCM #cryptography #GaloisCounterMode #opinion #SecurityGuidance #symmetricCryptography