refactor: replace legacy random coins with Poseidon2-based RandomCoin (#871)

Author: Al-Kindi-0

CHANGELOG.md

@@ -17,6 +17,7 @@
 - [BREAKING] Added info context field to secret box, bind IES HKDF info to a stable context string, scheme identifier, and ephemeral public key bytes. ([#843](https://github.com/0xMiden/crypto/pull/843)).
 - [BREAKING] Removed `PartialEq`/`Eq` for AEAD `SecretKey` in non-test builds, fix various hygiene issues in dealing with secret keys ([#849](https://github.com/0xMiden/crypto/pull/849)).
 - Added `PublicKey::from_der()` for ECDSA public keys over secp256k1 ([#855](https://github.com/0xMiden/crypto/pull/855)).
+- [BREAKING] Removed `RpoRandomCoin` and `RpxRandomCoin` and introduced a Poseidon2-based `RandomCoin` ([#871](https://github.com/0xMiden/crypto/pull/871)).
 
 ## 0.22.4 (2026-03-03)
 

README.md

@@ -117,11 +117,13 @@ Messages sealed as one type must be unsealed using the corresponding method, oth
 
 ## Pseudo-Random Element Generator
 
-[Pseudo random element generator module](./miden-crypto/src/rand/) provides a set of traits and data structures that facilitate generating pseudo-random elements in the context of Miden protocol. The module currently includes:
+[Pseudo random element generator module](./miden-crypto/src/rand/) provides a set of traits and utilities that facilitate generating pseudo-random elements in the context of Miden protocol. The module currently includes:
 
+- `Randomizable`: a trait for constructing values from random bytes.
 - `FeltRng`: a trait for generating random field elements and random 4 field elements.
-- `RpoRandomCoin`: a struct implementing `FeltRng` as well as the [`RandomCoin`](https://github.com/facebook/winterfell/blob/main/crypto/src/random/mod.rs) trait using RPO hash function.
-- `RpxRandomCoin`: a struct implementing `FeltRng` as well as the [`RandomCoin`](https://github.com/facebook/winterfell/blob/main/crypto/src/random/mod.rs) trait using RPX hash function.
+- `RandomCoin`: a struct implementing `FeltRng` using the Poseidon2 hash function.
+- `random_felt` and `random_word`: `std`-only helpers for generating random field elements and words.
+- `test_utils`: deterministic and `std`-based helpers for tests and benchmarks.
 
 ## STARK proving system
 

miden-crypto/Cargo.toml

@@ -64,11 +64,6 @@ harness           = false
 name              = "word"
 required-features = ["std"]
 
-[[bench]]
-harness           = false
-name              = "rand"
-required-features = ["std"]
-
 [[bench]]
 harness           = false
 name              = "sparse_path"