README: update security section

README.md

@@ -301,7 +301,48 @@ Format-preserving encryption algorithm (FPE-FF1) specified in NIST Special Publi
 
 ## Security
 
-The library is experimental. Use at your own risk.
+The library has not been independently audited yet.
+
+It is tested against property-based, cross-library and Wycheproof vectors,
+and has fuzzing by [Guido Vranken's cryptofuzz](https://github.com/guidovranken/cryptofuzz).
+
+### Constant-timeness
+
+_JIT-compiler_ and _Garbage Collector_ make "constant time" extremely hard to
+achieve [timing attack](https://en.wikipedia.org/wiki/Timing_attack) resistance
+in a scripting language. Which means _any other JS library can't have
+constant-timeness_. Even statically typed Rust, a language without GC,
+[makes it harder to achieve constant-time](https://www.chosenplaintext.ca/open-source/rust-timing-shield/security)
+for some cases. If your goal is absolute security, don't use any JS lib — including bindings to native ones.
+Use low-level libraries & languages. Nonetheless we're targetting algorithmic constant time.
+
+### Supply chain security
+
+1. **Commits** are signed with PGP keys, to prevent forgery. Make sure to verify commit signatures.
+2. **Releases** are transparent and built on GitHub CI. Make sure to verify [provenance](https://docs.npmjs.com/generating-provenance-statements) logs
+3. **Rare releasing** is followed.
+   The less often it is done, the less code dependents would need to audit
+4. **Dependencies** are minimal:
+   - All deps are prevented from automatic updates and have locked-down version ranges. Every update is checked with `npm-diff`
+   - Updates themselves are rare, to ensure rogue updates are not catched accidentally
+5. devDependencies are only used if you want to contribute to the repo. They are disabled for end-users:
+   - scure-base, micro-bmark and micro-should are developed by the same author and follow identical security practices
+   - prettier (linter), fast-check (property-based testing) and typescript are used for code quality, vector generation and ts compilation. The packages are big, which makes it hard to audit their source code thoroughly and fully
+
+We consider infrastructure attacks like rogue NPM modules very important;
+that's why it's crucial to minimize the amount of 3rd-party dependencies & native bindings.
+If your app uses 500 dependencies, any dep could get hacked and you'll be
+downloading malware with every install. Our goal is to minimize this attack vector.
+
+If you see anything unusual: investigate and report.
+
+### Randomness
+
+We're deferring to built-in
+[crypto.getRandomValues](https://developer.mozilla.org/en-US/docs/Web/API/Crypto/getRandomValues)
+which is considered cryptographically secure (CSPRNG).
+
+In the past, browsers had bugs that made it weak: it may happen again.
 
 ### How to encrypt properly
 

SECURITY.md

@@ -1,5 +1,7 @@
 # Security Policy
 
+See [README's Security section](./README.md#security) for detailed description of internal security practices.
+
 ## Supported Versions
 
 | Version | Supported          |