rand_jitter: Discourage use for cryptographic purposes

This is a breaking change, because `JitterRng` no longer implements `CryptoRng`. Fixes rust-random#699.
vks · Jun 3, 2019 · e0bffb2 · e0bffb2
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diff --git a/rand_jitter/README.md b/rand_jitter/README.md
@@ -9,6 +9,10 @@
 
 Non-physical true random number generator based on timing jitter.
 
+Note that this RNG is not suited for use cases where cryptographic security is
+required (also see [this
+discussion](https://github.com/rust-random/rand/issues/699)).
+
 This crate depends on [rand_core](https://crates.io/crates/rand_core) and is
 part of the [Rand project](https://github.com/rust-random/rand).
 

diff --git a/rand_jitter/src/lib.rs b/rand_jitter/src/lib.rs
@@ -14,6 +14,9 @@
 
 //! Non-physical true random number generator based on timing jitter.
 //!
+//! Note that this RNG is not suited for use cases where cryptographic security is
+//! required (also see this [discussion]).
+//!
 //! This is a true random number generator, as opposed to pseudo-random
 //! generators. Random numbers generated by `JitterRng` can be seen as fresh
 //! entropy. A consequence is that it is orders of magnitude slower than `OsRng`
@@ -24,9 +27,6 @@
 //! indistinguishable, and a cryptographic PRNG should also be as impossible to
 //! predict.
 //!
-//! Use of `JitterRng` is recommended for initializing cryptographic PRNGs when
-//! `OsRng` is not available.
-//!
 //! `JitterRng` can be used without the standard library, but not conveniently,
 //! you must provide a high-precision timer and carefully have to follow the
 //! instructions of [`JitterRng::new_with_timer`].
@@ -39,6 +39,7 @@
 //! with disabled `std` feature.
 //!
 //! [Jitterentropy]: http://www.chronox.de/jent.html
+//! [discussion]: https://github.com/rust-random/rand/issues/699
 
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
        html_favicon_url = "https://www.rust-lang.org/favicon.ico",
@@ -81,7 +82,7 @@ doc_comment!(include_str!("../README.md"));
 mod platform;
 mod error;
 
-use rand_core::{RngCore, CryptoRng, Error, impls};
+use rand_core::{RngCore, Error, impls};
 pub use error::TimerError;
 
 use core::{fmt, mem, ptr};
@@ -97,6 +98,9 @@ const MEMORY_SIZE: usize = MEMORY_BLOCKS * MEMORY_BLOCKSIZE;
 
 /// A true random number generator based on jitter in the CPU execution time,
 /// and jitter in memory access time.
+///
+/// Note that this RNG is not suitable for use cases where cryptographic
+/// security is required.
 pub struct JitterRng {
     data: u64, // Actual random number
     // Number of rounds to run the entropy collector per 64 bits
@@ -724,6 +728,3 @@ impl RngCore for JitterRng {
         Ok(self.fill_bytes(dest))
     }
 }
-
-impl CryptoRng for JitterRng {}
-