diff --git a/composer.json b/composer.json
index b51b1e0..2321393 100644
--- a/composer.json
+++ b/composer.json
@@ -13,6 +13,7 @@
     ],
     "require": {
         "php": ">=5.3",
+        "ext-mcrypt": "*",
         "christian-riesen/base32": "~1",
         "eloquent/enumeration": "~4",
         "icecave/isolator": "~2"
diff --git a/composer.lock b/composer.lock
index cd75c86..c973941 100644
--- a/composer.lock
+++ b/composer.lock
@@ -3,7 +3,7 @@
         "This file locks the dependencies of your project to a known state",
         "Read more about it at http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file"
     ],
-    "hash": "41e7b0062b41224d2d3bb7a8f1807d7b",
+    "hash": "e5c2d2b5b7d786f466d8253fbd1f37ed",
     "packages": [
         {
             "name": "christian-riesen/base32",
@@ -1316,7 +1316,8 @@
         "icecave/archer": 15
     },
     "platform": {
-        "php": ">=5.3"
+        "php": ">=5.3",
+        "ext-mcrypt": "*"
     },
     "platform-dev": [
 
diff --git a/src/Eloquent/Otis/Configuration/CounterBasedOtpConfigurationInterface.php b/src/Eloquent/Otis/Configuration/CounterBasedOtpConfigurationInterface.php
new file mode 100644
index 0000000..cb81568
--- /dev/null
+++ b/src/Eloquent/Otis/Configuration/CounterBasedOtpConfigurationInterface.php
@@ -0,0 +1,34 @@
+<?php
+
+/*
+ * This file is part of the Otis package.
+ *
+ * Copyright © 2013 Erin Millard
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Eloquent\Otis\Configuration;
+
+/**
+ * The interface implemented by counter-based one-time password multi-factor
+ * authentication configurations.
+ */
+interface CounterBasedOtpConfigurationInterface extends
+    MfaConfigurationInterface
+{
+    /**
+     * Get the amount of counter increments to search through for a match.
+     *
+     * @return integer The amount of counter increments to search through for a match.
+     */
+    public function window();
+
+    /**
+     * Get the initial counter value.
+     *
+     * @return integer The initial counter value.
+     */
+    public function initialCounter();
+}
diff --git a/src/Eloquent/Otis/Hotp/Configuration/HotpConfigurationInterface.php b/src/Eloquent/Otis/Hotp/Configuration/HotpConfigurationInterface.php
index f4f787b..20a1fac 100644
--- a/src/Eloquent/Otis/Hotp/Configuration/HotpConfigurationInterface.php
+++ b/src/Eloquent/Otis/Hotp/Configuration/HotpConfigurationInterface.php
@@ -11,22 +11,13 @@
 
 namespace Eloquent\Otis\Hotp\Configuration;
 
+use Eloquent\Otis\Configuration\CounterBasedOtpConfigurationInterface;
+
 /**
  * The interface implemented by HOTP configurations.
  */
-interface HotpConfigurationInterface extends HotpBasedConfigurationInterface
+interface HotpConfigurationInterface extends
+    HotpBasedConfigurationInterface,
+    CounterBasedOtpConfigurationInterface
 {
-    /**
-     * Get the amount of counter increments to search through for a match.
-     *
-     * @return integer The amount of counter increments to search through for a match.
-     */
-    public function window();
-
-    /**
-     * Get the initial counter value.
-     *
-     * @return integer The initial counter value.
-     */
-    public function initialCounter();
 }
diff --git a/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGenerator.php b/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGenerator.php
new file mode 100644
index 0000000..3a13c80
--- /dev/null
+++ b/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGenerator.php
@@ -0,0 +1,91 @@
+<?php
+
+/*
+ * This file is part of the Otis package.
+ *
+ * Copyright © 2013 Erin Millard
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Eloquent\Otis\Parameters\Generator;
+
+use Eloquent\Otis\Configuration\MfaConfigurationInterface;
+use Eloquent\Otis\Exception\UnsupportedArgumentsException;
+use Eloquent\Otis\Parameters\MfaSharedParametersInterface;
+use Icecave\Isolator\Isolator;
+
+/**
+ * Generates counter-based one-time password shared parameters.
+ */
+class CounterBasedOtpSharedParametersGenerator implements
+    MfaSharedParametersGeneratorInterface,
+    CounterBasedOtpSharedParametersGeneratorInterface
+{
+    /**
+     * Construct a new counter-based one-time password shared parameter generator.
+     *
+     * @param Isolator|null $isolator The isolator to use.
+     */
+    public function __construct(Isolator $isolator = null)
+    {
+        $this->isolator = Isolator::get($isolator);
+    }
+
+    /**
+     * Returns true if this generator supports the supplied configuration.
+     *
+     * @param MfaConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return boolean True if the configuration is supported.
+     */
+    public function supports(MfaConfigurationInterface $configuration)
+    {
+        return $configuration instanceof CounterBasedOtpConfigurationInterface;
+    }
+
+    /**
+     * Generate a set of shared parameters.
+     *
+     * @param MfaConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return MfaSharedParametersInterface  The generated shared parameters.
+     * @throws UnsupportedArgumentsException If the configuration type is not supported.
+     */
+    public function generate(MfaConfigurationInterface $configuration)
+    {
+        if (!$this->supports($configuration)) {
+            throw new UnsupportedArgumentsException;
+        }
+
+        return $this->generateCounterBased($configuration);
+    }
+
+    /**
+     * Generate a set of counter-based one-time password shared parameters.
+     *
+     * @param CounterBasedOtpConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return CounterBasedOtpSharedParametersInterface The generated shared parameters.
+     */
+    public function generateCounterBased(
+        CounterBasedOtpConfigurationInterface $configuration
+    ) {
+        return new CounterBasedOtpSharedParameters(
+            $this->isolator()->mcrypt_create_iv($configuration->secretLength())
+        );
+    }
+
+    /**
+     * Get the isolator.
+     *
+     * @return Isolator The isolator.
+     */
+    public function isolator()
+    {
+        return $this->isolator;
+    }
+
+    private $isolator;
+}
diff --git a/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGeneratorInterface.php b/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGeneratorInterface.php
new file mode 100644
index 0000000..bc1ca17
--- /dev/null
+++ b/src/Eloquent/Otis/Parameters/Generator/CounterBasedOtpSharedParametersGeneratorInterface.php
@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * This file is part of the Otis package.
+ *
+ * Copyright © 2013 Erin Millard
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Eloquent\Otis\Parameters\Generator;
+
+use Eloquent\Otis\Configuration\CounterBasedOtpConfigurationInterface;
+use Eloquent\Otis\Parameters\CounterBasedOtpSharedParametersInterface;
+
+/**
+ * The interface implemented by counter-based one-time password multi-factor
+ * authentication shared parameter generators.
+ */
+interface CounterBasedOtpSharedParametersGeneratorInterface
+{
+    /**
+     * Generate a set of counter-based one-time password shared parameters.
+     *
+     * @param CounterBasedOtpConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return CounterBasedOtpSharedParametersInterface The generated shared parameters.
+     */
+    public function generateCounterBased(
+        CounterBasedOtpConfigurationInterface $configuration
+    );
+}
diff --git a/src/Eloquent/Otis/Parameters/Generator/MfaSharedParametersGeneratorInterface.php b/src/Eloquent/Otis/Parameters/Generator/MfaSharedParametersGeneratorInterface.php
new file mode 100644
index 0000000..5c7fec5
--- /dev/null
+++ b/src/Eloquent/Otis/Parameters/Generator/MfaSharedParametersGeneratorInterface.php
@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the Otis package.
+ *
+ * Copyright © 2013 Erin Millard
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Eloquent\Otis\Parameters\Generator;
+
+use Eloquent\Otis\Configuration\MfaConfigurationInterface;
+use Eloquent\Otis\Parameters\MfaSharedParametersInterface;
+
+/**
+ * The interface implemented by multi-factor authentication shared parameter
+ * generators.
+ */
+interface MfaSharedParametersGeneratorInterface
+{
+    /**
+     * Returns true if this generator supports the supplied configuration.
+     *
+     * @param MfaConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return boolean True if the configuration is supported.
+     */
+    public function supports(MfaConfigurationInterface $configuration);
+
+    /**
+     * Generate a set of shared parameters.
+     *
+     * @param MfaConfigurationInterface $configuration The configuration to generate shared parameters for.
+     *
+     * @return MfaSharedParametersInterface  The generated shared parameters.
+     * @throws UnsupportedArgumentsException If the configuration type is not supported.
+     */
+    public function generate(MfaConfigurationInterface $configuration);
+}