There has been a lot of discussion recently around the LastPass breach, especially with regards to the number of PBKDF2 iterations applied to the master password to derive the vault encryption key. Other people have already dissected this particular breach, but I want to more generally talk about PBKDF2 iterations and security models. (I’m not going to talk about Argon2 or Bcrypt or any other algorithms).Continue reading “On PBKDF2 iterations”
Just a few quick notes/updates to correct some potentially inaccurate statements that are floating around on Reddit/Twitter etc:
- The bug only impacts Java 15 and above. The original advisory from Oracle incorrectly listed earlier versions (like 7, 8 and 11) as being impacted. They have since corrected this. Note that they now only list 17 and 18, because 15 and 16 are no longer supported.
- Bouncy Castle is not impacted by this vulnerability. They have their own ECDSA implementation, and it performs the relevant check to prevent this bug.
- Although an all-zero signature value is the simplest way to exploit this, there are several alternative values that exhibit the same bug. As previously mentioned, Project Wycheproof has an excellent selection of test vectors for this bug and many variations on it, in different signature formats, and for different elliptic curves.
- On a related note, some JWT libraries were initially assumed to be unaffected because a quirk of re-encoding raw (IEEE P1363) format signatures into ASN.1 format rejected zero values. But, as pointed out above, there are other invalid values that are not rejected by this conversion that still trigger the bug. Either upgrade your JVM, or your JWT library, and ideally both.
- Some JWT libraries also apparently accept signature values in several alternative encodings, so if you are checking for bad signatures in a pre-processing step then you have even more values to check. Again, best to update to get the patches rather than trying to fix this yourself.
The long-running BBC sci-fi show Doctor Who has a recurring plot device where the Doctor manages to get out of trouble by showing an identity card which is actually completely blank. Of course, this being Doctor Who, the card is really made out of a special “psychic paper“, which causes the person looking at it to see whatever the Doctor wants them to see: a security pass, a warrant, or whatever.
It turns out that some recent releases of Java were vulnerable to a similar kind of trick, in the implementation of widely-used ECDSA signatures. If you are running one of the vulnerable versions then an attacker can easily forge some types of SSL certificates and handshakes (allowing interception and modification of communications), signed JWTs, SAML assertions or OIDC id tokens, and even WebAuthn authentication messages. All using the digital equivalent of a blank piece of paper.
It’s hard to overstate the severity of this bug. If you are using ECDSA signatures for any of these security mechanisms, then an attacker can trivially and completely bypass them if your server is running any Java 15, 16, 17, or 18 version before the April 2022 Critical Patch Update (CPU). For context, almost all WebAuthn/FIDO devices in the real world (including Yubikeys*) use ECDSA signatures and many OIDC providers use ECDSA-signed JWTs.
If you have deployed Java 15, Java 16, Java 17, or Java 18 in production then you should stop what you are doing and immediately update to install the fixes in the April 2022 Critical Patch Update.
the official announcement from Oracle also lists older versions of Java, including 7, 8 and 11. Although I’m not aware of the bug impacting those older implementations they did fix a similar bug in the (non-EC) DSA implementation at the same time, so it’s possible older versions are also impacted. There are also other security vulnerabilities reported in the same CPU, so (as always) it is worth upgrading even if you are running an older Java version. The OpenJDK advisory on the other hand lists only versions 15, 17, and 18 as affected by this specific issue (CVE-2022-21449).
Update 2: Oracle have informed me they are in the process of correcting the advisory to state that only versions 15-18 are impacted. The CVE has already been updated. Note that 15 and 16 are no longer supported, so it will only list 17 and 18 as impacted.Continue reading “CVE-2022-21449: Psychic Signatures in Java”
This is the third part of my series on Key Encapsulation Mechanisms (KEMs) and why you should care about them. Part 1 looked at what a KEM is and the KEM/DEM paradigm for constructing public key encryption schemes. Part 2 looked at cases where the basic KEM abstraction is not sufficient and showed how it can be extended to add support for multiple recipients and sender authentication. At the end of part 2, I promised to write a follow-up about tackling forward-secrecy and replay attacks in the KEM/DEM paradigm, so here it is. In this article we’ll go from simple one-way message encryption to a toy version of the Signal Protocol that provides forward secrecy and strong authentication of two (or more) parties.
WARNING: please pay attention to the word “toy” in the previous sentence. This is a blog post, not a thorough treatment of how to write a real end-to-end encrypted messaging protocol.Continue reading “From KEMs to protocols”
In my previous post, I described the KEM/DEM paradigm for hybrid encryption. The key encapsulation mechanism is given the recipient’s public key and outputs a fresh AES key and an encapsulation of that key that the recipient can decapsulate to recover the AES key. In this post I want to talk about several ways that the KEM interface falls short and what to do about it:
- As I’ve discussed before, the standard definition of public key encryption lacks any authentication of the sender, and the KEM-DEM paradigm is no exception. You often want to have some idea of where a message came from before you process it, so how can we add sender authentication?
- If you want to send the same message to multiple recipients, a natural approach would be to encrypt the message once with a fresh AES key and then encrypt the AES key for each recipient. With the KEM approach though we’ll end up with a separate AES key for each recipient. How can we send the same message to multiple recipients without encrypting the whole thing separately for each one?
- Finally, the definition of public key encryption used in the KEM/DEM paradigm doesn’t provide forward secrecy. If an attacker ever compromises the recipient’s long-term private key, they can decrypt every message ever sent to that recipient. Can we prevent this?
In this article I’ll tackle the first two issues and show how the KEM/DEM abstractions can be adjusted to cope with each. In a follow-up post I’ll then show how to tackle forward secrecy, along with replay attacks and other issues. Warning: this post is longer and has more technical details than the previous post. It’s really meant for people who already have some experience with cryptographic algorithms.Continue reading “When a KEM is not enough”
If you know a bit about public key cryptography, you probably know that you don’t directly encrypt a message with a public key encryption algorithm like RSA. This is for many reasons, one of which being that it is incredibly slow. Instead you do what’s called hybrid encryption: first you generate a random AES key (*) and encrypt the message with that (using a suitable authenticated encryption mode), then you encrypt the AES key with the RSA public key. The recipient uses their RSA private key to decrypt the AES key and then uses that to decrypt the rest of the message. This is much faster than trying to encrypt a large message directly with RSA, so pretty much all sane implementations of RSA encryption do this.Continue reading “Hybrid encryption and the KEM/DEM paradigm”
In Part I, I made the argument that even when using public key cryptography you almost always want authenticated encryption. In this second part, we’ll look at how you can actually achieve public key authenticated encryption (PKAE) from commonly available building blocks. We will concentrate only on approaches that do not require an interactive protocol. (Updated 12th January 2019 to add a description of a NIST-approved key-agreement mode that achieves PKAE).
If you read or watch any recent tutorial on symmetric (or “secret key”) cryptography, one lesson should be clear: in 2018 if you want to encrypt something you’d better use authenticated encryption. This not only hides the content of a message, but also ensures that the message was sent by one of the parties that has access to the shared secret key and that it hasn’t been tampered with. It turns out that without these additional guarantees (integrity and authenticity), the contents of a message often does not remain secret for long either. Continue reading “Public key authenticated encryption and why you want it (Part I)”
Java KeyStores are used to store key material and associated certificates in an encrypted and integrity protected fashion. Like all things Java, this mechanism is pluggable and so there exist a variety of different options. There are lots of articles out there that describe the different types and how you can initialise them, load keys and certificates, etc. However, there is a lack of detailed technical information about exactly how these keystores store and protect your key material. This post attempts to gather those important details in one place for the most common KeyStores.
Continue reading “Java KeyStores – the gory details”