move rust_salt_hash_data

diff --git a/src/rust/bitbox02-rust-c/src/firmware_c_api.rs b/src/rust/bitbox02-rust-c/src/firmware_c_api.rs
index 988e8a5..c5da0bf 100644
--- a/src/rust/bitbox02-rust-c/src/firmware_c_api.rs
+++ b/src/rust/bitbox02-rust-c/src/firmware_c_api.rs
@@ -1,7 +1,32 @@
 // SPDX-License-Identifier: Apache-2.0
 
+use core::ffi::c_char;
+use util::bytes::{Bytes, BytesMut};
+
 #[cfg(not(any(feature = "c-unit-testing", feature = "simulator-graphical")))]
 #[unsafe(no_mangle)]
 pub extern "C" fn rust_main_loop() -> ! {
     bitbox02_rust::main_loop::main_loop(&mut crate::HalImpl::new())
 }
+
+/// # Safety
+///
+/// `purpose` must be a valid, null-terminated UTF-8 string pointer.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn rust_salt_hash_data(
+    data: Bytes,
+    purpose: *const c_char,
+    mut hash_out: BytesMut,
+) -> bool {
+    let purpose_str = match unsafe { util::strings::str_from_null_terminated_ptr(purpose) } {
+        Ok(purpose) => purpose,
+        Err(()) => return false,
+    };
+    match bitbox02_rust::salt::hash_data(&mut crate::HalImpl::new(), data.as_ref(), purpose_str) {
+        Ok(hash) => {
+            hash_out.as_mut()[..32].copy_from_slice(&hash);
+            true
+        }
+        Err(()) => false,
+    }
+}
diff --git a/src/rust/bitbox02-rust/src/salt.rs b/src/rust/bitbox02-rust/src/salt.rs
index 95b70f5..1442637 100644
--- a/src/rust/bitbox02-rust/src/salt.rs
+++ b/src/rust/bitbox02-rust/src/salt.rs
@@ -1,11 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use alloc::vec::Vec;
-use core::ffi::c_char;
 
 use crate::hal::Memory;
 use sha2::Digest;
-use util::bytes::{Bytes, BytesMut};
 use zeroize::Zeroizing;
 
 /// Creates `SHA256(salt_root || purpose || data)`, where `salt_root` is a persisted value that
@@ -28,36 +26,12 @@ pub fn hash_data(
     Ok(Zeroizing::new(hasher.finalize().to_vec()))
 }
 
-/// # Safety
-///
-/// `purpose` must be a valid, null-terminated UTF-8 string pointer.
-#[unsafe(no_mangle)]
-pub unsafe extern "C" fn rust_salt_hash_data(
-    data: Bytes,
-    purpose: *const c_char,
-    mut hash_out: BytesMut,
-) -> bool {
-    let purpose_str = match unsafe { util::strings::str_from_null_terminated_ptr(purpose) } {
-        Ok(purpose) => purpose,
-        Err(()) => return false,
-    };
-    let mut hal = crate::hal::BitBox02Hal::new();
-    match hash_data(&mut hal, data.as_ref(), purpose_str) {
-        Ok(hash) => {
-            hash_out.as_mut()[..32].copy_from_slice(&hash);
-            true
-        }
-        Err(()) => false,
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::hal::testing::TestingHal;
-    use bitbox02::{memory, testing::mock_memory};
+    use bitbox02::testing::mock_memory;
     use core::convert::TryInto;
-    use core::ptr;
     use hex_lit::hex;
 
     const MOCK_SALT_ROOT: [u8; 32] =
@@ -87,41 +61,4 @@ mod tests {
         let hash = hash_data(&mut mock_hal, &[], "").unwrap();
         assert_eq!(hash.as_slice(), &expected);
     }
-
-    #[test]
-    fn test_rust_salt_hash_data() {
-        mock_memory();
-        memory::set_salt_root(&MOCK_SALT_ROOT).unwrap();
-
-        let data = hex!("001122334455667788");
-        let expected = hex!("62db8dcd47ddf8e81809c377ed96643855d3052bb73237100ca81f0f5a7611e6");
-
-        let mut hash_out = [0u8; 32];
-        let purpose = c"test purpose";
-        assert!(unsafe {
-            rust_salt_hash_data(
-                util::bytes::rust_util_bytes(data.as_ptr(), data.len()),
-                purpose.as_ptr(),
-                util::bytes::rust_util_bytes_mut(hash_out.as_mut_ptr(), hash_out.len()),
-            )
-        });
-        assert_eq!(hash_out, expected);
-    }
-
-    #[test]
-    fn test_rust_salt_hash_data_empty_inputs() {
-        mock_memory();
-        memory::set_salt_root(&MOCK_SALT_ROOT).unwrap();
-
-        let expected = hex!("2dbb05dd73d94edba6946611aaca367f76c809e96f20499ad674e596050f9833");
-        let mut hash_out = [0u8; 32];
-        assert!(unsafe {
-            rust_salt_hash_data(
-                util::bytes::rust_util_bytes(ptr::null(), 0),
-                c"".as_ptr(),
-                util::bytes::rust_util_bytes_mut(hash_out.as_mut_ptr(), hash_out.len()),
-            )
-        });
-        assert_eq!(hash_out, expected);
-    }
 }