Exposing the derive_key() function under the danger feature (#73)

src/common.rs

@@ -356,7 +356,7 @@ where
 /////////////////////
 
 /// Can only fail with [`Error::DeriveKeyPair`] and [`Error::Protocol`].
-pub(crate) fn derive_key<CS: CipherSuite>(
+pub(crate) fn derive_key_internal<CS: CipherSuite>(
     seed: &[u8],
     info: &[u8],
     mode: Mode,
@@ -388,6 +388,20 @@ where
     Err(Error::Protocol)
 }
 
+/// Can only fail with [`Error::DeriveKeyPair`] and [`Error::Protocol`].
+#[cfg(feature = "danger")]
+pub fn derive_key<CS: CipherSuite>(
+    seed: &[u8],
+    info: &[u8],
+    mode: Mode,
+) -> Result<<CS::Group as Group>::Scalar, Error>
+where
+    <CS::Hash as OutputSizeUser>::OutputSize:
+        IsLess<U256> + IsLessOrEqual<<CS::Hash as BlockSizeUser>::BlockSize>,
+{
+    derive_key_internal::<CS>(seed, info, mode)
+}
+
 type DeriveKeypairResult<CS> = (
     <<CS as CipherSuite>::Group as Group>::Scalar,
     <<CS as CipherSuite>::Group as Group>::Elem,
@@ -403,7 +417,7 @@ where
     <CS::Hash as OutputSizeUser>::OutputSize:
         IsLess<U256> + IsLessOrEqual<<CS::Hash as BlockSizeUser>::BlockSize>,
 {
-    let sk_s = derive_key::<CS>(seed, info, mode)?;
+    let sk_s = derive_key_internal::<CS>(seed, info, mode)?;
     let pk_s = CS::Group::base_elem() * &sk_s;
 
     Ok((sk_s, pk_s))

src/lib.rs

@@ -500,6 +500,8 @@ mod tests;
 // Exports
 
 pub use crate::ciphersuite::CipherSuite;
+#[cfg(feature = "danger")]
+pub use crate::common::derive_key;
 pub use crate::common::{
     BlindedElement, EvaluationElement, Mode, PreparedEvaluationElement, Proof,
 };

src/oprf.rs

@@ -17,8 +17,8 @@ use generic_array::GenericArray;
 use rand_core::{CryptoRng, RngCore};
 
 use crate::common::{
-    derive_key, deterministic_blind_unchecked, i2osp_2, BlindedElement, EvaluationElement, Mode,
-    STR_FINALIZE,
+    derive_key_internal, deterministic_blind_unchecked, i2osp_2, BlindedElement, EvaluationElement,
+    Mode, STR_FINALIZE,
 };
 #[cfg(feature = "serde")]
 use crate::serialization::serde::Scalar;
@@ -189,7 +189,7 @@ where
     ///   then `u16::MAX - 3`.
     /// - [`Error::Protocol`] if the protocol fails and can't be completed.
     pub fn new_from_seed(seed: &[u8], info: &[u8]) -> Result<Self> {
-        let sk = derive_key::<CS>(seed, info, Mode::Oprf)?;
+        let sk = derive_key_internal::<CS>(seed, info, Mode::Oprf)?;
         Ok(Self { sk })
     }