diff --git a/AUTHORS b/AUTHORS
old mode 100644
new mode 100755
diff --git a/LICENSE b/LICENSE
old mode 100644
new mode 100755
diff --git a/README.rst b/README.rst
old mode 100644
new mode 100755
diff --git a/des.c b/des.c
old mode 100644
new mode 100755
index ada929c..6287b4c
--- a/des.c
+++ b/des.c
@@ -11,7 +11,7 @@ int initial_key_permutaion[] = {57, 49,  41, 33,  25,  17,  9,
 								63, 55,  47, 39,  31,  23, 15,
 								 7, 62,  54, 46,  38,  30, 22,
 								14,  6,  61, 53,  45,  37, 29,
-								21, 13,   5, 28,  20,  12,  4};
+								21, 13,   5, 28,  20,  12,  4};//选择置换PC-1，密钥置换64-56
 
 int initial_message_permutation[] =	   {58, 50, 42, 34, 26, 18, 10, 2,
 										60, 52, 44, 36, 28, 20, 12, 4,
@@ -20,9 +20,9 @@ int initial_message_permutation[] =	   {58, 50, 42, 34, 26, 18, 10, 2,
 										57, 49, 41, 33, 25, 17,  9, 1,
 										59, 51, 43, 35, 27, 19, 11, 3,
 										61, 53, 45, 37, 29, 21, 13, 5,
-										63, 55, 47, 39, 31, 23, 15, 7};
+										63, 55, 47, 39, 31, 23, 15, 7};//初始置换IP，明文代换，64-64，分两块
 
-int key_shift_sizes[] = {-1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1};
+int key_shift_sizes[] = {-1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1};//左移位数，16次
 
 int sub_key_permutation[] =    {14, 17, 11, 24,  1,  5,
 								 3, 28, 15,  6, 21, 10,
@@ -31,7 +31,7 @@ int sub_key_permutation[] =    {14, 17, 11, 24,  1,  5,
 								41, 52, 31, 37, 47, 55,
 								30, 40, 51, 45, 33, 48,
 								44, 49, 39, 56, 34, 53,
-								46, 42, 50, 36, 29, 32};
+								46, 42, 50, 36, 29, 32};//选择置换PC-2，56-48，得子密钥
 
 int message_expansion[] =  {32,  1,  2,  3,  4,  5,
 							 4,  5,  6,  7,  8,  9,
@@ -40,7 +40,7 @@ int message_expansion[] =  {32,  1,  2,  3,  4,  5,
 							16, 17, 18, 19, 20, 21,
 							20, 21, 22, 23, 24, 25,
 							24, 25, 26, 27, 28, 29,
-							28, 29, 30, 31, 32,  1};
+							28, 29, 30, 31, 32,  1};//扩展变换E，R扩展，32-48
 
 int S1[] = {14,  4, 13,  1,  2, 15, 11,  8,  3, 10,  6, 12,  5,  9,  0,  7,
 			 0, 15,  7,  4, 14,  2, 13,  1, 10,  6, 12, 11,  9,  5,  3,  8,
@@ -80,7 +80,7 @@ int S7[] = { 4, 11,  2, 14, 15,  0,  8, 13,  3, 12,  9,  7,  5, 10,  6,  1,
 int S8[] = {13,  2,  8,  4,  6, 15, 11,  1, 10,  9,  3, 14,  5,  0, 12,  7,
 			 1, 15, 13,  8, 10,  3,  7,  4, 12,  5,  6, 11,  0, 14,  9,  2,
 			 7, 11,  4,  1,  9, 12, 14,  2,  0,  6, 10, 13, 15,  3,  5,  8,
-			 2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11};
+			 2,  1, 14,  7,  4, 10,  8, 13, 15, 12,  9,  0,  3,  5,  6, 11};//八个S盒，替换异或后的8组
 
 int right_sub_message_permutation[] =    {16,  7, 20, 21,
 									29, 12, 28, 17,
@@ -89,7 +89,7 @@ int right_sub_message_permutation[] =    {16,  7, 20, 21,
 									 2,  8, 24, 14,
 									32, 27,  3,  9,
 									19, 13, 30,  6,
-									22, 11,  4, 25};
+									22, 11,  4, 25};//P置换，S盒后的32位代换
 
 int final_message_permutation[] =  {40,  8, 48, 16, 56, 24, 64, 32,
 									39,  7, 47, 15, 55, 23, 63, 31,
@@ -98,7 +98,7 @@ int final_message_permutation[] =  {40,  8, 48, 16, 56, 24, 64, 32,
 									36,  4, 44, 12, 52, 20, 60, 28,
 									35,  3, 43, 11, 51, 19, 59, 27,
 									34,  2, 42, 10, 50, 18, 58, 26,
-									33,  1, 41,  9, 49, 17, 57, 25};
+									33,  1, 41,  9, 49, 17, 57, 25};//初始逆置换IP
 
 
 void print_char_as_binary(char input) {
@@ -115,8 +115,10 @@ void print_char_as_binary(char input) {
 
 void generate_key(unsigned char* key) {
 	int i;
+	printf("Please input your key(less than 8 bytes)\n");
 	for (i=0; i<8; i++) {
-		key[i] = rand()%255;
+		scanf("%c",&key[i]);
+		//key[i] = rand()%255;
 	}
 }
 
diff --git a/des.h b/des.h
old mode 100644
new mode 100755
diff --git a/instructions.txt b/instructions.txt
new file mode 100644
index 0000000..d2046cf
--- /dev/null
+++ b/instructions.txt
@@ -0,0 +1,7 @@
+gcc -O3 des.c run_des.c -o run_des.o
+
+./run_des.o -g keyfile.key
+
+./run_des.o -e keyfile.key sample.txt sample.enc
+
+./run_des.o -d keyfile.key sample.enc sample_decrypted.txt
diff --git a/run_des.c b/run_des.c
old mode 100644
new mode 100755