add Cmac::new_with_algorithm for rust callers

src/rust/src/backend/cmac.rs

@@ -14,22 +14,54 @@ use crate::{exceptions, types};
     module = "cryptography.hazmat.bindings._rust.openssl.cmac",
     name = "CMAC"
 )]
-struct Cmac {
+pub(crate) struct Cmac {
     ctx: Option<cryptography_openssl::cmac::Cmac>,
 }
 
 impl Cmac {
-    fn new_bytes(key: &[u8], cipher: &openssl::cipher::CipherRef) -> CryptographyResult<Self> {
+    pub(crate) fn new_bytes(
+        key: &[u8],
+        cipher: &openssl::cipher::CipherRef,
+    ) -> CryptographyResult<Self> {
         let ctx = cryptography_openssl::cmac::Cmac::new(key, cipher)?;
         Ok(Cmac { ctx: Some(ctx) })
     }
 
-    fn update_bytes(&mut self, data: &[u8]) -> CryptographyResult<()> {
+    pub(crate) fn new_with_algorithm(
+        py: pyo3::Python<'_>,
+        algorithm: &pyo3::Bound<'_, pyo3::PyAny>,
+    ) -> CryptographyResult<Self> {
+        if !algorithm.is_instance(&types::BLOCK_CIPHER_ALGORITHM.get(py)?)? {
+            return Err(CryptographyError::from(
+                pyo3::exceptions::PyTypeError::new_err(
+                    "Expected instance of BlockCipherAlgorithm.",
+                ),
+            ));
+        }
+
+        let cipher = cipher_registry::get_cipher(py, algorithm.clone(), types::CBC.get(py)?)?
+            .ok_or_else(|| {
+                exceptions::UnsupportedAlgorithm::new_err((
+                    "CMAC is not supported with this algorithm",
+                    exceptions::Reasons::UNSUPPORTED_CIPHER,
+                ))
+            })?;
+
+        let key = algorithm
+            .getattr(pyo3::intern!(py, "key"))?
+            .extract::<CffiBuf<'_>>()?;
+
+        Cmac::new_bytes(key.as_bytes(), cipher)
+    }
+
+    pub(crate) fn update_bytes(&mut self, data: &[u8]) -> CryptographyResult<()> {
         self.get_mut_ctx()?.update(data)?;
         Ok(())
     }
 
-    fn finalize_bytes(&mut self) -> CryptographyResult<cryptography_openssl::hmac::DigestBytes> {
+    pub(crate) fn finalize_bytes(
+        &mut self,
+    ) -> CryptographyResult<cryptography_openssl::hmac::DigestBytes> {
         let data = self.get_mut_ctx()?.finish()?;
         self.ctx = None;
         Ok(data)
@@ -61,27 +93,7 @@ impl Cmac {
     ) -> CryptographyResult<Self> {
         let _ = backend;
 
-        if !algorithm.is_instance(&types::BLOCK_CIPHER_ALGORITHM.get(py)?)? {
-            return Err(CryptographyError::from(
-                pyo3::exceptions::PyTypeError::new_err(
-                    "Expected instance of BlockCipherAlgorithm.",
-                ),
-            ));
-        }
-
-        let cipher = cipher_registry::get_cipher(py, algorithm.clone(), types::CBC.get(py)?)?
-            .ok_or_else(|| {
-                exceptions::UnsupportedAlgorithm::new_err((
-                    "CMAC is not supported with this algorithm",
-                    exceptions::Reasons::UNSUPPORTED_CIPHER,
-                ))
-            })?;
-
-        let key = algorithm
-            .getattr(pyo3::intern!(py, "key"))?
-            .extract::<CffiBuf<'_>>()?;
-
-        Cmac::new_bytes(key.as_bytes(), cipher)
+        Cmac::new_with_algorithm(py, &algorithm)
     }
 
     fn update(&mut self, data: CffiBuf<'_>) -> CryptographyResult<()> {