Add SHA256 and SHA512 bindings to bssl-crypto

Bug: 285222360
Change-Id: I7f35bcc734dd853e99cb691bdc681f75c9f137e4
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/60265
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: Bob Beck <bbe@google.com>

rust/bssl-crypto/src/digest.rs

@@ -13,6 +13,8 @@
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+use core::marker::PhantomData;
+
 use crate::ForeignTypeRef;
 
 /// The BoringSSL implemented SHA-256 digest algorithm.
@@ -26,6 +28,7 @@ pub struct Sha512 {}
 /// A reference to an [`Md`], which abstracts the details of a specific hash function allowing code
 /// to deal with the concept of a "hash function" without needing to know exactly which hash function
 /// it is.
+#[non_exhaustive]
 pub struct MdRef;
 
 unsafe impl ForeignTypeRef for MdRef {
@@ -51,6 +54,15 @@ impl Md for Sha256 {
     }
 }
 
+impl Sha256 {
+    /// Create a new [digest] to compute the SHA256 hash.
+    pub fn new_digest() -> Digest<Self, { Self::OUTPUT_SIZE }> {
+        // Note: This cannot be in the trait because using associated constants exprs there
+        // requires nightly.
+        Digest::<Self, { Self::OUTPUT_SIZE }>::new()
+    }
+}
+
 impl Md for Sha512 {
     const OUTPUT_SIZE: usize = bssl_sys::SHA512_DIGEST_LENGTH as usize;
 
@@ -61,8 +73,98 @@ impl Md for Sha512 {
     }
 }
 
+impl Sha512 {
+    /// Create a new [digest] to compute the SHA512 hash.
+    pub fn new_digest() -> Digest<Self, { Self::OUTPUT_SIZE }> {
+        // Note: This cannot be in the trait because using associated constants exprs there
+        // requires nightly.
+        Digest::<Self, { Self::OUTPUT_SIZE }>::new()
+    }
+}
+
+/// A struct for computing the digest
+pub struct Digest<M: Md, const OUTPUT_SIZE: usize>(bssl_sys::EVP_MD_CTX, PhantomData<M>);
+
+impl<M: Md, const OUTPUT_SIZE: usize> Digest<M, OUTPUT_SIZE> {
+
+    /// Create a new Digest from the given `Md` type parameter.
+    ///
+    /// Panics:
+    /// - If `Md::OUTPUT_SIZE` is not the same as `OUTPUT_SIZE`.
+    fn new() -> Self {
+        // Note: runtime assertion needed here since using {M::OUTPUT_SIZE} in return type requires
+        // unstable Rust feature.
+        assert_eq!(M::OUTPUT_SIZE, OUTPUT_SIZE);
+        let mut md_ctx_uninit = core::mem::MaybeUninit::<bssl_sys::EVP_MD_CTX>::uninit();
+        // Safety:
+        // - `EVP_DigestInit` initializes `md_ctx_uninit`
+        // - `MdRef` ensures the validity of `md.as_ptr`
+        let result =
+            unsafe { bssl_sys::EVP_DigestInit(md_ctx_uninit.as_mut_ptr(), M::get_md().as_ptr()) };
+        assert_eq!(result, 1, "bssl_sys::EVP_DigestInit failed");
+        // Safety:
+        // - md_ctx_uninit initialized with EVP_DigestInit, and the function returned 1 (success)
+        let md_ctx = unsafe { md_ctx_uninit.assume_init() };
+        Self(md_ctx, PhantomData)
+    }
+
+    /// Updates this digest computation using the given `data`.
+    pub fn update(&mut self, data: &[u8]) {
+        // Safety:
+        // - `data` is a slice from safe Rust.
+        let result = unsafe {
+            bssl_sys::EVP_DigestUpdate(&mut self.0, data.as_ptr() as *const _, data.len())
+        };
+        assert_eq!(result, 1, "bssl_sys::EVP_DigestUpdate failed");
+    }
+
+    /// Consumes this digest and returns the output digest value.
+    #[allow(clippy::expect_used)]
+    pub fn finalize(mut self) -> [u8; OUTPUT_SIZE] {
+        let mut digest_uninit =
+            core::mem::MaybeUninit::<[u8; bssl_sys::EVP_MAX_MD_SIZE as usize]>::uninit();
+        let mut len_uninit = core::mem::MaybeUninit::<u32>::uninit();
+        // Safety:
+        // - `digest_uninit` is allocated to `EVP_MAX_MD_SIZE` bytes long, as required by
+        //   EVP_DigestFinal_ex
+        // - `self.0` is owned by `self`, and is going to be cleaned up on drop.
+        let result = unsafe {
+            bssl_sys::EVP_DigestFinal_ex(
+                &mut self.0,
+                digest_uninit.as_mut_ptr() as *mut _,
+                len_uninit.as_mut_ptr(),
+            )
+        };
+        assert_eq!(result, 1, "bssl_sys::EVP_DigestFinal_ex failed");
+        // Safety:
+        // - `len_uninit` is initialized by `EVP_DigestFinal_ex`, and we checked the result above
+        let len = unsafe { len_uninit.assume_init() };
+        assert_eq!(
+            OUTPUT_SIZE, len as usize,
+            "bssl_sys::EVP_DigestFinal_ex failed"
+        );
+        // Safety: Result of DigestFinal_ex was checked above
+        let digest = unsafe { digest_uninit.assume_init() };
+        digest
+            .get(..OUTPUT_SIZE)
+            .and_then(|digest| digest.try_into().ok())
+            .expect("The length of `digest` was checked above")
+    }
+}
+
+impl<M: Md, const OUTPUT_SIZE: usize> Drop for Digest<M, OUTPUT_SIZE> {
+    fn drop(&mut self) {
+        // Safety: `self.0` is owned by `self`, and is invalidated after `drop`.
+        unsafe {
+            bssl_sys::EVP_MD_CTX_cleanup(&mut self.0);
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
+    use crate::test_helpers::decode_hex;
+
     use super::*;
 
     #[test]
@@ -84,4 +186,33 @@ mod test {
             )
         }
     }
+
+    #[test]
+    fn test_digest_sha256() {
+        let mut digest = Sha256::new_digest();
+        let msg: [u8; 4] = decode_hex("74ba2521");
+        digest.update(&msg);
+        let expected_digest: [u8; 32] =
+            decode_hex("b16aa56be3880d18cd41e68384cf1ec8c17680c45a02b1575dc1518923ae8b0e");
+        assert_eq!(expected_digest, digest.finalize());
+    }
+
+    #[test]
+    fn test_digest_sha512() {
+        let mut digest = Sha512::new_digest();
+        let msg: [u8; 4] = decode_hex("23be86d5");
+        digest.update(&msg);
+        let expected_digest: [u8; 64] = decode_hex(concat!(
+            "76d42c8eadea35a69990c63a762f330614a4699977f058adb988f406fb0be8f2",
+            "ea3dce3a2bbd1d827b70b9b299ae6f9e5058ee97b50bd4922d6d37ddc761f8eb"
+        ));
+        assert_eq!(expected_digest, digest.finalize());
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_digest_wrong_size() {
+        // This should not happen since we don't externally expose Digest::new
+        Digest::<Sha256, 64>::new();
+    }
 }