1 files changed, 49 insertions, 0 deletions
diff --git a/src/cnki_kdh.c b/src/cnki_kdh.c
new file mode 100644
index 0000000..8441319
--- /dev/null
+++ b/src/cnki_kdh.c
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2020, yzrh <yzrh@tuta.io>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "cnki.h"
+
+int
+cnki_kdh(cnki_t **param)
+{
+	if (*param == NULL)
+		return 1;
+
+	if ((*param)->stat > 0)
+		printf("Begin 'KDH' decryption\n");
+
+	fseek((*param)->fp_i, 0, SEEK_END);
+
+	long size = ftell((*param)->fp_i);
+
+	fseek((*param)->fp_i, ADDRESS_KDH_BODY, SEEK_SET);
+
+	const char key[] = KEY_KDH;
+	const int key_len = KEY_KDH_LENGTH;
+	long key_cur = 0;
+
+	char buf[(*param)->size_buf];
+
+	for (;;) {
+		fread(buf, (*param)->size_buf, 1, (*param)->fp_i);
+
+		for (int i = 0; i < (*param)->size_buf; i++) {
+			buf[i] ^= key[key_cur % key_len];
+			key_cur++;
+		}
+
+		fwrite(buf, (*param)->size_buf, 1, (*param)->fp_o);
+
+		if (ftell((*param)->fp_i) == size)
+			break;
+	}
+
+	if ((*param)->stat > 0)
+		printf("Decryption ended total %ld byte(s) written\n",
+			ftell((*param)->fp_o));
+
+	return 0;
+}