pv/examples: Add example for calculating host-key hashes

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv/examples/hash_hkd/main.rs

@@ -0,0 +1,28 @@
+#![allow(missing_docs)]
+
+use pv::request::EcPubKeyCoord;
+use pv_core::misc::encode_hex;
+use s390_pv as pv;
+
+use std::env::args;
+
+use pv::misc::{read_certs, read_file};
+use pv::{Error, Result};
+
+fn main() -> Result<()> {
+    let hkd = args().nth(1).expect("Expect one Host-key document");
+    let hkd_bin = read_file(&hkd, "Host-key document")?;
+    let certs = read_certs(hkd_bin).map_err(|source| Error::HkdNotPemOrDer { hkd, source })?;
+    let hkd_cert = certs
+        .first()
+        .expect("Expect at least one certificate in the HKD file");
+
+    let pc: EcPubKeyCoord = hkd_cert
+        .public_key()
+        .expect("Expected a public key in the Host-key document")
+        .try_into()
+        .unwrap();
+
+    println!("{}", encode_hex(pc.sha256().unwrap()));
+    Ok(())
+}