[crypto] Add support for HKDF key derivation

Add support for the HMAC-based Extract-and-Expand Key Derivation
Function (HKDF) as used in TLS version 1.3 and defined in RFC 5869.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/hkdf.h

@@ -0,0 +1,22 @@
+#ifndef _IPXE_HKDF_H
+#define _IPXE_HKDF_H
+
+/** @file
+ *
+ * HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+FILE_SECBOOT ( PERMITTED );
+
+#include <ipxe/crypto.h>
+
+extern void hkdf_extract ( struct digest_algorithm *digest, const void *salt,
+			   size_t salt_len, const void *ikm, size_t ikm_len,
+			   void *prk );
+extern void hkdf_expand ( struct digest_algorithm *digest, const void *prk,
+			  const void *info, size_t info_len, void *out,
+			  size_t len );
+
+#endif /* _IPXE_HKDF_H */