crypto: Adapt kdf_t interface to support KDFs with fixed output length

src/libstrongswan/crypto/crypto_tester.c

@@ -1309,6 +1309,17 @@ METHOD(crypto_tester_t, test_kdf, bool,
 		{
 			goto failure;
 		}
+		if (kdf_has_fixed_output_length(alg))
+		{
+			if (kdf->get_length(kdf) != vector->out.len)
+			{
+				goto failure;
+			}
+		}
+		else if (kdf->get_length(kdf) != SIZE_MAX)
+		{
+			goto failure;
+		}
 		/* allocated bytes */
 		if (!kdf->allocate_bytes(kdf, vector->out.len, &out))
 		{
@@ -1318,6 +1329,19 @@ METHOD(crypto_tester_t, test_kdf, bool,
 		{
 			goto failure;
 		}
+		/* allocate without knowing the length */
+		if (kdf_has_fixed_output_length(alg))
+		{
+			chunk_free(&out);
+			if (!kdf->allocate_bytes(kdf, 0, &out))
+			{
+				goto failure;
+			}
+			if (!chunk_equals(out, vector->out))
+			{
+				goto failure;
+			}
+		}
 		/* bytes to existing buffer */
 		memset(out.ptr, 0, out.len);
 		if (!kdf->get_bytes(kdf, out.len, out.ptr))

src/libstrongswan/crypto/kdfs/kdf.c

@@ -26,3 +26,17 @@ ENUM(key_derivation_function_names, KDF_UNDEFINED, KDF_PRF_PLUS,
 	"KDF_UNDEFINED",
 	"KDF_PRF_PLUS",
 );
+
+/*
+ * Described in header
+ */
+bool kdf_has_fixed_output_length(key_derivation_function_t type)
+{
+	switch (type)
+	{
+		case KDF_PRF_PLUS:
+		case KDF_UNDEFINED:
+			break;
+	}
+	return FALSE;
+}

src/libstrongswan/crypto/kdfs/kdf.h

@@ -85,9 +85,18 @@ struct kdf_t {
 	 */
 	key_derivation_function_t (*get_type)(kdf_t *this);
 
+	/**
+	 * Output length for KDFs that produce a fixed amount of output.
+	 *
+	 * @return			fixed output length, SIZE_MAX for variable length
+	 */
+	size_t (*get_length)(kdf_t *this);
+
 	/**
 	 * Derives a key of the given length and writes it to the buffer.
 	 *
+	 * @note Fails if out_len doesn't match for KDFs with fixed output length.
+	 *
 	 * @param out_len	number of key bytes requested
 	 * @param buffer	pointer where the derived key will be written
 	 * @return			TRUE if key derived successfully
@@ -98,7 +107,12 @@ struct kdf_t {
 	/**
 	 * Derives a key of the given length and allocates space for it.
 	 *
-	 * @param out_len	number of key bytes requested
+	 * @note Fails if out_len doesn't match for KDFs with fixed output length.
+	 * However, for simplified usage, 0 can be passed for out_len to
+	 * automatically allocate a chunk of the correct size.
+	 *
+	 * @param out_len	number of key bytes requested, or 0 for KDFs with fixed
+	 *					output length
 	 * @param chunk		chunk which will hold the derived key
 	 * @return			TRUE if key derived successfully
 	 */
@@ -121,4 +135,12 @@ struct kdf_t {
 	void (*destroy)(kdf_t *this);
 };
 
+/**
+ * Check if the given KDF type has a fixed output length.
+ *
+ * @param type			KDF type
+ * @return				TRUE if the KDF type has a fixed output length
+ */
+bool kdf_has_fixed_output_length(key_derivation_function_t type);
+
 #endif /** KDF_H_ @}*/

src/libstrongswan/plugins/botan/botan_kdf.c

@@ -71,6 +71,12 @@ METHOD(kdf_t, get_type, key_derivation_function_t,
 	return KDF_PRF_PLUS;
 }
 
+METHOD(kdf_t, get_length, size_t,
+	private_kdf_t *this)
+{
+	return SIZE_MAX;
+}
+
 METHOD(kdf_t, get_bytes, bool,
 	private_kdf_t *this, size_t out_len, uint8_t *buffer)
 {
@@ -162,6 +168,7 @@ kdf_t *botan_kdf_create(key_derivation_function_t algo, va_list args)
 	INIT(this,
 		.public = {
 			.get_type = _get_type,
+			.get_length = _get_length,
 			.get_bytes = _get_bytes,
 			.allocate_bytes = _allocate_bytes,
 			.set_param = _set_param,

src/libstrongswan/plugins/kdf/kdf_prf_plus.c

@@ -51,6 +51,12 @@ METHOD(kdf_t, get_type, key_derivation_function_t,
 	return KDF_PRF_PLUS;
 }
 
+METHOD(kdf_t, get_length, size_t,
+	private_kdf_t *this)
+{
+	return SIZE_MAX;
+}
+
 METHOD(kdf_t, get_bytes, bool,
 	private_kdf_t *this, size_t out_len, uint8_t *buffer)
 {
@@ -156,6 +162,7 @@ kdf_t *kdf_prf_plus_create(key_derivation_function_t algo, va_list args)
 	INIT(this,
 		.public = {
 			.get_type = _get_type,
+			.get_length = _get_length,
 			.get_bytes = _get_bytes,
 			.allocate_bytes = _allocate_bytes,
 			.set_param = _set_param,

src/libstrongswan/plugins/openssl/openssl_kdf.c

@@ -66,6 +66,12 @@ METHOD(kdf_t, get_type, key_derivation_function_t,
 	return KDF_PRF_PLUS;
 }
 
+METHOD(kdf_t, get_length, size_t,
+	private_kdf_t *this)
+{
+	return SIZE_MAX;
+}
+
 METHOD(kdf_t, get_bytes, bool,
 	private_kdf_t *this, size_t out_len, uint8_t *buffer)
 {
@@ -153,6 +159,7 @@ kdf_t *openssl_kdf_create(key_derivation_function_t algo, va_list args)
 	INIT(this,
 		.public = {
 			.get_type = _get_type,
+			.get_length = _get_length,
 			.get_bytes = _get_bytes,
 			.allocate_bytes = _allocate_bytes,
 			.set_param = _set_param,

src/libstrongswan/plugins/wolfssl/wolfssl_kdf.c

@@ -64,6 +64,12 @@ METHOD(kdf_t, get_type, key_derivation_function_t,
 	return KDF_PRF_PLUS;
 }
 
+METHOD(kdf_t, get_length, size_t,
+	private_kdf_t *this)
+{
+	return SIZE_MAX;
+}
+
 METHOD(kdf_t, get_bytes, bool,
 	private_kdf_t *this, size_t out_len, uint8_t *buffer)
 {
@@ -141,6 +147,7 @@ kdf_t *wolfssl_kdf_create(key_derivation_function_t algo, va_list args)
 	INIT(this,
 		.public = {
 			.get_type = _get_type,
+			.get_length = _get_length,
 			.get_bytes = _get_bytes,
 			.allocate_bytes = _allocate_bytes,
 			.set_param = _set_param,