Define additional ConfidentialStore around RSA key pair

core/src/main/java/jenkins/security/RSAConfidentialKey.java

+package jenkins.security;
+
+import org.apache.commons.codec.binary.Base64;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.security.KeyFactory;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.PrivateKey;
+import java.security.SecureRandom;
+import java.security.interfaces.RSAPrivateCrtKey;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.PKCS8EncodedKeySpec;
+import java.security.spec.RSAPublicKeySpec;
+
+/**
+ * RSA public/private key pair as {@link ConfidentialKey}.
+ *
+ * <p>
+ * As per the design principle of {@link ConfidentialKey}, not exposing {@link PrivateKey} directly.
+ * Define subtypes for different use cases.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public abstract class RSAConfidentialKey extends ConfidentialKey {
+    private volatile RSAPrivateKey priv;
+    private volatile RSAPublicKey pub;
+    public RSAConfidentialKey(String id) {
+        super(id);
+    }
+
+    public RSAConfidentialKey(Class owner, String shortName) {
+        this(owner.getName() + '.' + shortName);
+    }
+
+    private RSAPrivateKey getKey() {
+        try {
+            if (priv ==null) {
+                synchronized (this) {
+                    if (priv ==null) {
+                        byte[] payload = load();
+                        if (payload==null) {
+                            KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
+                            gen.initialize(2048,new SecureRandom()); // going beyond 2048 requires crypto extension
+                            KeyPair keys = gen.generateKeyPair();
+                            priv = (RSAPrivateKey)keys.getPrivate();
+                            pub  = (RSAPublicKey)keys.getPublic();
+                            store(priv.getEncoded());
+                        } else {
+                            KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+                            priv = (RSAPrivateKey)keyFactory.generatePrivate(new PKCS8EncodedKeySpec(payload));
+
+                            RSAPrivateCrtKey pks = (RSAPrivateCrtKey) priv;
+                            pub = (RSAPublicKey)keyFactory.generatePublic(
+                                    new RSAPublicKeySpec(pks.getModulus(), pks.getPublicExponent()));
+                        }
+                    }
+                }
+            }
+            return priv;
+        } catch (IOException e) {
+            throw new Error("Failed to load the key: "+getId(),e);
+        } catch (GeneralSecurityException e) {
+            throw new Error("Failed to load the key: "+getId(),e);
+        }
+    }
+
+    /**
+     * Caller is responsible for using the private key appropriately to avoid compromise.
+     */
+    protected RSAPrivateKey getPrivateKey() {
+        return getKey();
+    }
+
+    public RSAPublicKey getPublicKey() {
+        getKey();
+        return pub;
+    }
+
+    /**
+     * Gets base64-encoded public key.
+     */
+    public String getEncodedPublicKey() {
+        return new String(Base64.encodeBase64(getPublicKey().getEncoded()));
+    }
+}

core/src/main/java/jenkins/security/RSADigitalSignatureConfidentialKey.java

+package jenkins.security;
+
+import hudson.remoting.Base64;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.security.Signature;
+import java.security.interfaces.RSAPrivateKey;
+
+/**
+ * RSA digital signature as {@link ConfidentialKey} to prevent accidental leak of private key.
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public class RSADigitalSignatureConfidentialKey extends RSAConfidentialKey {
+    public RSADigitalSignatureConfidentialKey(String id) {
+        super(id);
+    }
+
+    public RSADigitalSignatureConfidentialKey(Class owner, String shortName) {
+        super(owner, shortName);
+    }
+
+    /**
+     * Sign a message and base64 encode the signature.
+     */
+    public String sign(String msg) throws GeneralSecurityException, IOException {
+        RSAPrivateKey key = getPrivateKey();
+        Signature sig = Signature.getInstance(SIGNING_ALGORITHM + "with" + key.getAlgorithm());
+        sig.initSign(key);
+        sig.update(msg.getBytes("UTF8"));
+        return Base64.encode(sig.sign());
+    }
+
+    static final String SIGNING_ALGORITHM = "SHA256";
+}

core/src/test/groovy/jenkins/security/RSAConfidentialKeyTest.groovy

+package jenkins.security
+
+import org.junit.Rule
+import org.junit.Test
+
+/**
+ *
+ *
+ * @author Kohsuke Kawaguchi
+ */
+class RSAConfidentialKeyTest {
+    @Rule
+    public ConfidentialStoreRule store = new ConfidentialStoreRule()
+
+    def key = new RSAConfidentialKey("test") {}
+
+    @Test
+    void loadingExistingKey() {
+        // this second key of the same ID will cause it to load the key from the disk
+        def key2 = new RSAConfidentialKey("test") {}
+
+        assert key.privateKey==key2.privateKey;
+        assert key.publicKey ==key2.publicKey;
+    }
+}