diff --git a/src/Cryptography/Keys/EcdsaPrivateKey.php b/src/Cryptography/Keys/EcdsaPrivateKey.php
index 54fc119..86411b4 100644
--- a/src/Cryptography/Keys/EcdsaPrivateKey.php
+++ b/src/Cryptography/Keys/EcdsaPrivateKey.php
@@ -33,7 +33,7 @@ public function __construct(string $key, string $passphrase = '', ?string $id =
     }
 
     /**
-     * @return mixed
+     * @return resource
      */
     public function getResource()
     {
diff --git a/src/Cryptography/Keys/EcdsaPublicKey.php b/src/Cryptography/Keys/EcdsaPublicKey.php
index c4fab54..b0161af 100644
--- a/src/Cryptography/Keys/EcdsaPublicKey.php
+++ b/src/Cryptography/Keys/EcdsaPublicKey.php
@@ -32,7 +32,7 @@ public function __construct(string $key, ?string $id = null)
     }
 
     /**
-     * @return mixed
+     * @return resource
      */
     public function getResource()
     {
diff --git a/src/Cryptography/Keys/RsaPrivateKey.php b/src/Cryptography/Keys/RsaPrivateKey.php
index 960e507..f558aa9 100644
--- a/src/Cryptography/Keys/RsaPrivateKey.php
+++ b/src/Cryptography/Keys/RsaPrivateKey.php
@@ -33,7 +33,7 @@ public function __construct(string $key, string $passphrase = '', ?string $id =
     }
 
     /**
-     * @return mixed
+     * @return resource
      */
     public function getResource()
     {
diff --git a/src/Cryptography/Keys/RsaPublicKey.php b/src/Cryptography/Keys/RsaPublicKey.php
index 0592ba2..2bd4632 100644
--- a/src/Cryptography/Keys/RsaPublicKey.php
+++ b/src/Cryptography/Keys/RsaPublicKey.php
@@ -32,7 +32,7 @@ public function __construct(string $key, ?string $id = null)
     }
 
     /**
-     * @return mixed
+     * @return resource
      */
     public function getResource()
     {