diff --git a/authfs/src/crypto.hpp b/authfs/src/crypto.hpp
new file mode 100644
index 0000000..58b0bd3
--- /dev/null
+++ b/authfs/src/crypto.hpp
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef AUTHFS_OPENSSL_WRAPPER_H
+#define AUTHFS_OPENSSL_WRAPPER_H
+
+#include <openssl/sha.h>
+
+#endif  // AUTHFS_OPENSSL_WRAPPER_H
diff --git a/authfs/src/crypto.rs b/authfs/src/crypto.rs
new file mode 100644
index 0000000..a51acca
--- /dev/null
+++ b/authfs/src/crypto.rs
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#![allow(dead_code)]
+
+use std::mem::MaybeUninit;
+
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum CryptoError {
+    #[error("Unexpected error returned from {0}")]
+    Unexpected(&'static str),
+}
+
+use authfs_crypto_bindgen::{SHA256_Final, SHA256_Init, SHA256_Update, SHA256_CTX};
+
+pub struct Sha256Hasher {
+    ctx: SHA256_CTX,
+}
+
+impl Sha256Hasher {
+    pub const HASH_SIZE: usize = 32;
+
+    pub fn new() -> Result<Sha256Hasher, CryptoError> {
+        // Safe assuming the crypto FFI should initialize the uninitialized `ctx`, which is
+        // currently a pure data struct.
+        unsafe {
+            let mut ctx = MaybeUninit::uninit();
+            if SHA256_Init(ctx.as_mut_ptr()) == 0 {
+                Err(CryptoError::Unexpected("SHA256_Init"))
+            } else {
+                Ok(Sha256Hasher { ctx: ctx.assume_init() })
+            }
+        }
+    }
+
+    pub fn update(&mut self, data: &[u8]) -> Result<&mut Self, CryptoError> {
+        // Safe assuming the crypto FFI will not touch beyond `ctx` as pure data.
+        let retval = unsafe {
+            SHA256_Update(&mut self.ctx, data.as_ptr() as *mut std::ffi::c_void, data.len())
+        };
+        if retval == 0 {
+            Err(CryptoError::Unexpected("SHA256_Update"))
+        } else {
+            Ok(self)
+        }
+    }
+
+    pub fn finalize(&mut self) -> Result<[u8; Self::HASH_SIZE], CryptoError> {
+        let mut md = [0u8; Self::HASH_SIZE];
+        // Safe assuming the crypto FFI will not touch beyond `ctx` as pure data.
+        let retval = unsafe { SHA256_Final(md.as_mut_ptr(), &mut self.ctx) };
+        if retval == 0 {
+            Err(CryptoError::Unexpected("SHA256_Final"))
+        } else {
+            Ok(md)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn to_hex_string(data: &[u8]) -> String {
+        data.iter().map(|&b| format!("{:02x}", b)).collect()
+    }
+
+    #[test]
+    fn verify_hash_values() -> Result<(), CryptoError> {
+        let hash = Sha256Hasher::new()?.update(&[0; 0])?.finalize()?;
+        let s: String = to_hex_string(&hash);
+        assert_eq!(s, "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
+
+        let hash = Sha256Hasher::new()?
+            .update(&[1u8; 1])?
+            .update(&[2u8; 1])?
+            .update(&[3u8; 1])?
+            .finalize()?;
+        let s: String = to_hex_string(&hash);
+        assert_eq!(s, "039058c6f2c0cb492c533b0a4d14ef77cc0f78abccced5287d84a1a2011cfb81");
+        Ok(())
+    }
+}
diff --git a/authfs/src/lib.rs b/authfs/src/lib.rs
index 6b136a4..c128f62 100644
--- a/authfs/src/lib.rs
+++ b/authfs/src/lib.rs
@@ -22,4 +22,5 @@
 //!
 //! The implementation is not finished.
 
+mod crypto;
 mod reader;