diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/impl/DefaultConnection.java b/acme4j-client/src/main/java/org/shredzone/acme4j/impl/DefaultConnection.java
index 6dd564c9..c46c333b 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/impl/DefaultConnection.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/impl/DefaultConnection.java
@@ -34,7 +34,6 @@ import java.util.regex.Pattern;
 import org.jose4j.base64url.Base64Url;
 import org.jose4j.json.JsonUtil;
 import org.jose4j.jwk.PublicJsonWebKey;
-import org.jose4j.jws.AlgorithmIdentifiers;
 import org.jose4j.jws.JsonWebSignature;
 import org.jose4j.lang.JoseException;
 import org.shredzone.acme4j.Registration;
@@ -47,6 +46,7 @@ import org.shredzone.acme4j.exception.AcmeRateLimitExceededException;
 import org.shredzone.acme4j.exception.AcmeServerException;
 import org.shredzone.acme4j.exception.AcmeUnauthorizedException;
 import org.shredzone.acme4j.util.ClaimBuilder;
+import org.shredzone.acme4j.util.SignatureUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -148,7 +148,7 @@ public class DefaultConnection implements Connection {
             jws.setPayload(claims.toString());
             jws.getHeaders().setObjectHeaderValue("nonce", Base64Url.encode(session.getNonce()));
             jws.getHeaders().setJwkHeaderValue("jwk", jwk);
-            jws.setAlgorithmHeaderValue(AlgorithmIdentifiers.RSA_USING_SHA256);
+            jws.setAlgorithmHeaderValue(SignatureUtils.keyAlgorithm(jwk));
             jws.setKey(keypair.getPrivate());
             byte[] outputData = jws.getCompactSerialization().getBytes("utf-8");
 
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/util/SignatureUtils.java b/acme4j-client/src/main/java/org/shredzone/acme4j/util/SignatureUtils.java
new file mode 100644
index 00000000..c32b8d8b
--- /dev/null
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/util/SignatureUtils.java
@@ -0,0 +1,70 @@
+/*
+ * acme4j - Java ACME client
+ *
+ * Copyright (C) 2016 Richard "Shred" Körber
+ *   http://acme4j.shredzone.org
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+package org.shredzone.acme4j.util;
+
+import org.jose4j.jwk.EllipticCurveJsonWebKey;
+import org.jose4j.jwk.JsonWebKey;
+import org.jose4j.jwk.RsaJsonWebKey;
+import org.jose4j.jws.AlgorithmIdentifiers;
+import org.jose4j.jws.JsonWebSignature;
+
+/**
+ * Utility class for signatures.
+ *
+ * @author Richard "Shred" Körber
+ */
+public final class SignatureUtils {
+
+    private SignatureUtils() {
+        // Utility class without constructor
+    }
+
+    /**
+     * Analyzes the key used in the {@link JsonWebKey}, and returns the key algorithm
+     * identifier for {@link JsonWebSignature}.
+     *
+     * @param jwk
+     *            {@link JsonWebKey} to analyze
+     * @return algorithm identifier
+     * @throws IllegalArgumentException
+     *             there is no corresponding algorithm identifier for the key
+     */
+    public static String keyAlgorithm(JsonWebKey jwk) {
+        if (jwk instanceof EllipticCurveJsonWebKey) {
+            EllipticCurveJsonWebKey ecjwk = (EllipticCurveJsonWebKey) jwk;
+
+            switch (ecjwk.getCurveName()) {
+                case "P-256":
+                    return AlgorithmIdentifiers.ECDSA_USING_P256_CURVE_AND_SHA256;
+
+                case "P-384":
+                    return AlgorithmIdentifiers.ECDSA_USING_P384_CURVE_AND_SHA384;
+
+                case "P-512":
+                    return AlgorithmIdentifiers.ECDSA_USING_P521_CURVE_AND_SHA512;
+
+                default:
+                    throw new IllegalArgumentException("Unknown EC name "
+                        + ecjwk.getCurveName());
+            }
+
+        } else if (jwk instanceof RsaJsonWebKey) {
+            return AlgorithmIdentifiers.RSA_USING_SHA256;
+
+        } else {
+            throw new IllegalArgumentException("Unknown algorithm " + jwk.getAlgorithm());
+        }
+    }
+
+}
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/util/ValidationBuilder.java b/acme4j-client/src/main/java/org/shredzone/acme4j/util/ValidationBuilder.java
index 5d10f5c0..14b96a22 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/util/ValidationBuilder.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/util/ValidationBuilder.java
@@ -21,7 +21,6 @@ import java.util.List;
 import java.util.Map;
 
 import org.jose4j.jwk.PublicJsonWebKey;
-import org.jose4j.jws.AlgorithmIdentifiers;
 import org.jose4j.jws.JsonWebSignature;
 import org.jose4j.lang.JoseException;
 import org.shredzone.acme4j.Registration;
@@ -112,7 +111,7 @@ public class ValidationBuilder {
             JsonWebSignature jws = new JsonWebSignature();
             jws.setPayload(claims.toString());
             jws.getHeaders().setJwkHeaderValue("jwk", jwk);
-            jws.setAlgorithmHeaderValue(AlgorithmIdentifiers.RSA_USING_SHA256);
+            jws.setAlgorithmHeaderValue(SignatureUtils.keyAlgorithm(jwk));
             jws.setKey(keypair.getPrivate());
             jws.sign();