diff --git a/src/main/java/de/mlessmann/certassist/openssl/OpenSSLCertificateCreator.java b/src/main/java/de/mlessmann/certassist/openssl/OpenSSLCertificateCreator.java
index b3d1007..18730c3 100644
--- a/src/main/java/de/mlessmann/certassist/openssl/OpenSSLCertificateCreator.java
+++ b/src/main/java/de/mlessmann/certassist/openssl/OpenSSLCertificateCreator.java
@@ -15,6 +15,7 @@ import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
 import java.util.List;
 import java.util.Optional;
+import java.util.UUID;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -25,7 +26,6 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.lang.NonNull;
-import org.springframework.lang.Nullable;
 import org.springframework.stereotype.Service;
 import org.springframework.util.CollectionUtils;
 import org.zeroturnaround.exec.ProcessExecutor;
@@ -135,6 +135,7 @@ public class OpenSSLCertificateCreator {
                     "genrsa",
                     "-out",
                     keyFile.toString(),
+                    "-aes256",
                     "-passout",
                     "env:KEY_PASS",
                     Integer.toString(request.getRequestedKeyLength())
@@ -282,20 +283,28 @@ public class OpenSSLCertificateCreator {
         }
     }
 
+    /**
+     * Checks whether the provided key file is encrypted using a passphrase
+     */
     public boolean isKeyEncrypted(@NonNull Path keyFile) throws InterruptedException, CommandLineOperationException {
-        // If any random passphrase works, the key is not encrypted.
-        return !verifyKeyPassphrase(keyFile, null);
+        // If the key is not encrypted, any passphrase will work -> so generate a random one to check.
+        String passphrase = UUID.randomUUID().toString();
+        boolean firstPass = verifyKeyPassphrase(keyFile, passphrase);
+        if (firstPass) {
+            // Try with another random passphrase in case we randomly got lucky guessing the passphrase the first time.
+            passphrase = UUID.randomUUID().toString();
+            return !verifyKeyPassphrase(keyFile, passphrase);
+        }
+        return true;
     }
 
     /**
      * Verifies a passphrase against a provided key.
-     * @implNote Due to the implementation of the OpenSSL cli, any password will be valid for unencrypted keys. (Check with {@link #isKeyEncrypted(Path) or by passing {@code null} as the passphrase.)
+     * @implNote Due to the implementation of the OpenSSL cli, <em>any password</em> will be valid for unencrypted keys. (Check with {@link #isKeyEncrypted(Path).)
      */
-    public boolean verifyKeyPassphrase(@NonNull Path keyFile, @Nullable String passphrase)
+    public boolean verifyKeyPassphrase(@NonNull Path keyFile, @NonNull String passphrase)
         throws CommandLineOperationException, InterruptedException {
-        // Run OpenSSL command: openssl rsa -check -in <keyFile> -passin pass:<randomKey> -noout and check exit code
         try {
-            String keyPass = passphrase != null ? passphrase : passwordProvider.generateNewPassword();
             StartedProcess verifyCommand = new ProcessExecutor()
                 .command(
                     resolveOpenSSL(),
@@ -304,16 +313,14 @@ public class OpenSSLCertificateCreator {
                     "-in",
                     keyFile.toString(),
                     "-passin",
-                    "pass:" + keyPass,
+                    "pass:" + passphrase,
                     "-noout"
                 )
                 .redirectOutput(Slf4jStream.ofCaller().asError())
                 .redirectError(Slf4jStream.ofCaller().asError())
                 .start();
             var verifyResult = verifyCommand.getFuture().get();
-            boolean commandSuccess = verifyResult.getExitValue() == 0;
-            log.trace("Key check {} with passphrase provided={}", commandSuccess, passphrase != null);
-            return commandSuccess;
+            return verifyResult.getExitValue() == 0;
         } catch (IOException | InterruptedException | ExecutionException e) {
             throw new CommandLineOperationException("Failed to verify key encryption", e);
         }