diff --git a/aos/sha256.cc b/aos/sha256.cc
new file mode 100644
index 0000000..ae83792
--- /dev/null
+++ b/aos/sha256.cc
@@ -0,0 +1,26 @@
+#include "aos/sha256.h"
+
+#include <iomanip>
+#include <sstream>
+#include <string>
+
+#include "absl/types/span.h"
+#include "openssl/sha.h"
+
+namespace aos {
+
+std::string Sha256(const absl::Span<const uint8_t> str) {
+  unsigned char hash[SHA256_DIGEST_LENGTH];
+  SHA256_CTX sha256;
+  SHA256_Init(&sha256);
+  SHA256_Update(&sha256, str.data(), str.size());
+  SHA256_Final(hash, &sha256);
+  std::stringstream ss;
+  for (int i = 0; i < SHA256_DIGEST_LENGTH; i++) {
+    ss << std::hex << std::setw(2) << std::setfill('0')
+       << static_cast<int>(hash[i]);
+  }
+  return ss.str();
+}
+
+}  // namespace aos