diff --git a/crypto-openssl.cpp b/crypto-openssl.cpp
index 6ae8293..48d7af5 100644
--- a/crypto-openssl.cpp
+++ b/crypto-openssl.cpp
@@ -48,8 +48,8 @@ struct Aes_impl {
 };
 
 Aes_ecb_encryptor::Aes_ecb_encryptor (const unsigned char* raw_key)
+: impl(new Aes_impl)
 {
-	impl = new Aes_impl;
 	if (AES_set_encrypt_key(raw_key, KEY_LEN * 8, &(impl->key)) != 0) {
 		throw Crypto_error("Aes_ctr_encryptor::Aes_ctr_encryptor", "AES_set_encrypt_key failed");
 	}
@@ -57,7 +57,8 @@ Aes_ecb_encryptor::Aes_ecb_encryptor (const unsigned char* raw_key)
 
 Aes_ecb_encryptor::~Aes_ecb_encryptor ()
 {
-	delete impl;
+	// Note: Explicit destructor necessary because class contains an auto_ptr
+	// which contains an incomplete type when the auto_ptr is declared.
 }
 
 void Aes_ecb_encryptor::encrypt(const unsigned char* plain, unsigned char* cipher)
@@ -70,15 +71,17 @@ struct Hmac_impl {
 };
 
 Hmac_sha1_state::Hmac_sha1_state (const unsigned char* key, size_t key_len)
+: impl(new Hmac_impl)
 {
-	impl = new Hmac_impl;
 	HMAC_Init(&(impl->ctx), key, key_len, EVP_sha1());
 }
 
 Hmac_sha1_state::~Hmac_sha1_state ()
 {
+	// Note: Explicit destructor necessary because class contains an auto_ptr
+	// which contains an incomplete type when the auto_ptr is declared.
+
 	HMAC_cleanup(&(impl->ctx));
-	delete impl;
 }
 
 void Hmac_sha1_state::add (const unsigned char* buffer, size_t buffer_len)
diff --git a/crypto.hpp b/crypto.hpp
index ae6a14c..4eedc07 100644
--- a/crypto.hpp
+++ b/crypto.hpp
@@ -36,6 +36,7 @@
 #include <stddef.h>
 #include <iosfwd>
 #include <string>
+#include <memory>
 
 void init_crypto ();
 
@@ -56,11 +57,7 @@ public:
 	};
 
 private:
-	Aes_impl*	impl;
-
-	// disallow copy/assignment:
-	Aes_ecb_encryptor (const Aes_ecb_encryptor&);
-	Aes_ecb_encryptor& operator= (const Aes_ecb_encryptor&);
+	std::auto_ptr<Aes_impl>	impl;
 
 public:
 	Aes_ecb_encryptor (const unsigned char* key);
@@ -104,11 +101,7 @@ public:
 	};
 
 private:
-	Hmac_impl*	impl;
-
-	// disallow copy/assignment:
-	Hmac_sha1_state (const Hmac_sha1_state&) { }
-	Hmac_sha1_state& operator= (const Hmac_sha1_state&) { return *this; }
+	std::auto_ptr<Hmac_impl>	impl;
 
 public:
 	Hmac_sha1_state (const unsigned char* key, size_t key_len);