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

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,