build(deps): bump rand to 0.10 and migrate RNG API usage

rand 0.8 -> 0.10 in driven-crypto (the only crate with a direct rand
dep). API migration per the rand 0.9/0.10 changelogs:

- `use rand::RngCore` -> `use rand::TryRng` (RngCore is a deprecated
  stub in rand_core 0.10; TryRng is the fallible base trait)
- `rand::rngs::OsRng.fill_bytes(buf)` ->
  `rand::rngs::SysRng.try_fill_bytes(buf).expect(...)` (OsRng was
  renamed SysRng and re-exported from getrandom 0.4; it only exposes
  the fallible TryRng surface, and .expect() preserves rand 0.8's
  behavior of panicking inside OsRng::fill_bytes on entropy failure)

Semantics preserved: every call site still fills raw byte buffers
straight from the OS CSPRNG (getrandom); no generator, seeding, or
distribution changes. chacha20poly1305 0.10 keeps its internal
rand_core 0.6 pin via aead 0.5, which is fine - driven-crypto never
passes an RNG into an aead API, so the two rand_core majors coexist.

Supersedes #85.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014fLmkjpFkiuky72eLBijL4

Author: pmaxhogan

Cargo.lock

@@ -34,6 +34,11 @@ keyring = { workspace = true }
 # for the verify-on-upload comparison.
 md5 = { workspace = true }
 # `getrandom`-backed RNG for the per-file STREAM nonce, the wrapped-key
-# nonce, and fresh master / per-source key material (DESIGN s7.1). Pinned to
-# 0.8 to match `chacha20poly1305` 0.10's `rand_core` 0.6 `OsRng`.
-rand = "0.8"
+# nonce, and fresh master / per-source key material (DESIGN s7.1).
+# `chacha20poly1305` 0.10 pulls in `aead` 0.5's own `rand_core` 0.6 `OsRng`
+# internally, but this crate never calls an `aead`/`chacha20poly1305` API
+# that accepts a caller-supplied RNG (no `encrypt_in_place_with_rng` /
+# `KeyInit::generate_key`) - every call site here fills a raw byte buffer
+# directly via `RngCore`/`TryRngCore`, so the two `rand_core` major versions
+# never need to match.
+rand = "0.10"

crates/driven-crypto/Cargo.toml

@@ -25,7 +25,7 @@ use chacha20poly1305::{
     KeyInit, XChaCha20Poly1305,
 };
 use md5::{Digest, Md5};
-use rand::RngCore;
+use rand::TryRng;
 
 use crate::key::{SourceKey, XNONCE_LEN};
 use crate::CryptoError;
@@ -65,7 +65,13 @@ impl ContentEncryptorImpl {
     /// Builds an encryptor for one file with a freshly generated nonce.
     pub(crate) fn new(source_key: &SourceKey) -> Self {
         let mut nonce = [0u8; XNONCE_LEN];
-        rand::rngs::OsRng.fill_bytes(&mut nonce);
+        // `SysRng` (rand 0.10's OS RNG, re-exported from `getrandom`) is
+        // fallible (`TryRng`, not the infallible `Rng`) since reading OS
+        // entropy can fail. `.expect()` preserves rand 0.8's `OsRng::fill_bytes`
+        // behavior, which panicked internally on the same failure.
+        rand::rngs::SysRng
+            .try_fill_bytes(&mut nonce)
+            .expect("OS RNG (getrandom) failed to fill content nonce");
         let cipher = XChaCha20Poly1305::new(source_key.as_bytes().as_ref().into());
         let stream_nonce = GenericArray::from_slice(&nonce[..STREAM_NONCE_LEN]);
         Self {

crates/driven-crypto/src/content.rs

@@ -10,7 +10,7 @@ use chacha20poly1305::{
     aead::{Aead, KeyInit},
     XChaCha20Poly1305, XNonce,
 };
-use rand::RngCore;
+use rand::TryRng;
 use zeroize::{Zeroize, ZeroizeOnDrop};
 
 use crate::CryptoError;
@@ -38,7 +38,13 @@ impl MasterKey {
     #[must_use]
     pub fn generate() -> Self {
         let mut bytes = [0u8; KEY_LEN];
-        rand::rngs::OsRng.fill_bytes(&mut bytes);
+        // See `content.rs::ContentEncryptorImpl::new` for why `SysRng` needs
+        // `try_fill_bytes` + `.expect()`: it's rand 0.10's fallible OS RNG,
+        // and `.expect()` preserves rand 0.8 `OsRng::fill_bytes`'s panic on
+        // the same underlying failure.
+        rand::rngs::SysRng
+            .try_fill_bytes(&mut bytes)
+            .expect("OS RNG (getrandom) failed to fill master key");
         Self(bytes)
     }
 
@@ -78,7 +84,9 @@ impl MasterKey {
     pub fn wrap_source_key(&self, source_key: &SourceKey) -> Result<WrappedSourceKey, CryptoError> {
         let cipher = XChaCha20Poly1305::new(self.0.as_ref().into());
         let mut nonce_bytes = [0u8; XNONCE_LEN];
-        rand::rngs::OsRng.fill_bytes(&mut nonce_bytes);
+        rand::rngs::SysRng
+            .try_fill_bytes(&mut nonce_bytes)
+            .expect("OS RNG (getrandom) failed to fill wrap nonce");
         let nonce = XNonce::from_slice(&nonce_bytes);
         let ciphertext = cipher
             .encrypt(nonce, source_key.0.as_ref())
@@ -120,7 +128,9 @@ impl SourceKey {
     #[must_use]
     pub fn generate() -> Self {
         let mut bytes = [0u8; KEY_LEN];
-        rand::rngs::OsRng.fill_bytes(&mut bytes);
+        rand::rngs::SysRng
+            .try_fill_bytes(&mut bytes)
+            .expect("OS RNG (getrandom) failed to fill source key");
         Self(bytes)
     }