Paragon Initiative Enterprises Blog

The latest information from the team that develops cryptographically secure PHP software.

Solving Open Source Supply Chain Security for the PHP Ecosystem

To assert that "There exist supply-chain security risks" in any software ecosystem doesn't require a formal analysis nor multiple experts to peer review such a notion. It's kind of a given, especially with recent tech news.

However, it's not a new problem. We were vocal about it in 2015, when it was common practice for software projects to tell you to install their widget by running curl http://some-domain | sh in a terminal window. This specific anti-pattern had already been criticized widely by others since at least 2013, but we were more interested in proposing a general solution to secure code delivery.

The only things that have really changed in the intervening years are:

  1. More people are aware of the risks today than 7 years ago,
  2. More disasters have been caused by the lack of supply-chain security for open source software, and
  3. We know it's a solvable problem.

That last item might seem bold, but we've been laying the groundwork for elegantly solving these problems for the PHP ecosystem since our company's inception. We had briefly introduced our complete solution when we announced that WordPress would cryptographically sign its automatic updates in 2019. (If you'd like more depth into this subject, we've previously written about supply-chain security in 2017 and automatic security updates in 2016.)

Part of making an acceptable solution even possible required getting modern cryptography into PHP and writing a pure-PHP polyfill of ext/sodium for legacy versions of PHP. (These are just two of the things that we're known for in the PHP community.)

So with all that in mind, let's take a quick look at Gossamer, our proposal for securing the software supply-chain for the PHP ecosystem.

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Promoting Misuse-Resistance in PASETO Libraries

Last month, Thomas Ptacek wrote API Tokens: A Tedious Survey on the fly.io blog, which talks about all things API Token.

His post covered JWT, PASETO (our design), and a few other token formats. He went on to clarify, on Hacker News, that:

The one thing I'm not super comfortable about here is my PASETO take. My attitude going in was that PASETO has a lot of boosters and not a lot of critical takes. I can beat up on Macaroons because we're using them, and I'm going to follow up with a post about what our Macaroons like like. I'm not doing that with PASETO. So, like, I stand by it, but take it for what it's worth.

What was his take, exactly? Our succinct understanding of the criticisms laid out in the fly.io article are as follows:

  1. There are too many versions; the old ones should be deprecated.
  2. PASETO's specification spells out how to avoid algorithm confusion for implementors.
  3. Decide between symmetric and asymmetric; don't support both use-cases.
  4. NIST algorithm support and CFRG involvement are unnecessary and possibly counterproductive.

Out of these criticisms, the first two are actionable and warrant further inspection, while the latter are Thomas's opinion.

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Introducing PASERK, the First PASETO Extension, for Key Wrapping and Serialization

When we designed PASETO, our goal was to provide an easy-to-use, secure-by-default, and simple protocol that solves the same sort of problems as JSON Web Tokens (except actually secure).

This resulted in two types of PASETO token being defined for each version of the protocol:

  1. Local tokens: Symmetric authenticated encryption
  2. Public tokens: Asymmetric digital signatures

This solved the majority of use cases, but not all: If you wanted to use public-key encryption instead of symmetric-key encryption, you couldn't accomplish that with PASETO. Put flatly, there was no JWK-equivalent for PASETO.

With that in mind, today we'd like to announce the first PASETO extension:

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PASETO is an Even More Secure Alternative to the JOSE Standards (JWT, etc.)

Three years ago, we introduced PASETO to the Internet, as an alternative to the insecure JOSE standards.

PASETO was designed with the philosophy of avoiding in-band negotiation, as well as recognizing that any cryptography key should always be considered to be the raw key material alongside its parameter choices. To that end, PASETO was built with versioned protocols at its foundation (and each key could only be used with a given version and purpose).

Today, we announce the next iteration of the PASETO specification, which includes two new protocols (Version 3 and Version 4).

  • Version 3 (if you need NIST-approved algorithms)
    • Local tokens (v3.local) use AES-256-CTR + HMAC-SHA384 (Encrypt-then-MAC)
    • Public tokens (v3.public) use ECDSA over NIST P-384
  • Version 4 (Recommended)
    • Local tokens (v4.local) use XChaCha20 + BLAKE2b-MAC (Encrypt-then-MAC)
      • This is very similar to what Halite has always done.
    • Public tokens (v4.public) use Ed25519.

Security teams will mostly be interested in the Rationale page in the PASETO Specification repository. Pay special attention to the section on ECDSA security and questions for security auditors.

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Ristretto255 for the PHP Community

Ristretto logo

Ristretto is a technique for constructing prime order elliptic curve groups with non-malleable encodings. It extends Mike Hamburg's Decaf approach to cofactor elimination to support cofactor-8 curves such as Curve25519.

Ristretto255 is Ristretto defined over Curve25519, which allows cryptographers to extend the Ed25519 signature scheme to support complex zero-knowledge proof protocols without having to deal with the cofactor.

(The cofactor in Ed25519 is what caused the multi-spend vulnerability in CryptoNote cryptocurrencies (n.b. Monero).)

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