diff --git a/subprojects/libcr51sign/libcr51sign_support.h b/subprojects/libcr51sign/libcr51sign_support.h
new file mode 100644
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+++ b/subprojects/libcr51sign/libcr51sign_support.h
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+/*
+ * Copyright 2021 Google LLC
+ *
+ * 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 PLATFORMS_HAVEN_LIBCR51SIGN_LIBCR51SIGN_SUPPORT_H_
+#define PLATFORMS_HAVEN_LIBCR51SIGN_LIBCR51SIGN_SUPPORT_H_
+
+#include "libcr51sign.h"
+
+#include <openssl/sha.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    struct hash_ctx
+    {
+        enum hash_type hash_type;
+        union
+        {
+            SHA256_CTX sha256_ctx;
+            SHA512_CTX sha512_ctx;
+        };
+    };
+
+    // @func hash_init get ready to compute a hash
+    //
+    // @param[in] ctx - context struct
+    // @param[in] hash_type - type of hash function to use
+    //
+    // @return nonzero on error, zero on success
+
+    int hash_init(const void* ctx, enum hash_type type);
+
+    // @func hash_update add data to the hash
+    //
+    // @param[in] ctx - context struct
+    // @param[in] buf - data to add to hash
+    // @param[in] count - number of bytes of data to add
+    //
+    // @return nonzero on error, zero on success
+
+    int hash_update(void* ctx, const uint8_t* data, size_t size);
+
+    // @func hash_final finish hash calculation
+    //
+    // @param[in] ctx - context struct
+    // @param[out] hash - buffer to write hash to (guaranteed to be big enough)
+    //
+    // @return nonzero on error, zero on success
+
+    int hash_final(void* ctx, uint8_t* hash);
+
+    // @func verify check that the signature is valid for given hashed data
+    //
+    // @param[in] ctx - context struct
+    // @param[in] scheme - type of signature, hash, etc.
+    // @param[in] sig - signature blob
+    // @param[in] sig_len - length of signature in bytes
+    // @param[in] data - pre-hashed data to verify
+    // @param[in] data_len - length of hashed data in bytes
+    //
+    // @return nonzero on error, zero on success
+
+    int verify_signature(const void* ctx, enum signature_scheme sig_scheme,
+                         const uint8_t* sig, size_t sig_len,
+                         const uint8_t* data, size_t data_len);
+
+#ifdef __cplusplus
+} //  extern "C"
+#endif
+#endif // PLATFORMS_HAVEN_LIBCR51SIGN_LIBCR51SIGN_SUPPORT_H_