diff --git a/mmc.c b/mmc.c
index bc8f74e..3ff7308 100644
--- a/mmc.c
+++ b/mmc.c
@@ -250,6 +250,17 @@ static struct Command commands[] = {
 		"be 1.",
 	NULL
 	},
+	{ do_lock_unlock, -3,
+	"cmd42", "<password> " "<parameter> " "<device>\n"
+		"Usage: mmc cmd42 <password> <s|c|l|u|e> <device>\n"
+		"s\tset password\n"
+		"c\tclear password\n"
+		"l\tlock\n"
+		"sl\tset password and lock\n"
+		"u\tunlock\n"
+		"e\tforce erase\n",
+	NULL
+	},
 	{ do_softreset, -1,
 	  "softreset", "<device>\n"
 	  "Issues a CMD0 softreset, e.g. for testing if hardware reset for UHS works",
diff --git a/mmc.h b/mmc.h
index 6f1bf3e..f8bac22 100644
--- a/mmc.h
+++ b/mmc.h
@@ -30,6 +30,7 @@
 #define MMC_SEND_STATUS		13	/* ac   [31:16] RCA        R1  */
 #define R1_SWITCH_ERROR   (1 << 7)  /* sx, c */
 #define MMC_SWITCH_MODE_WRITE_BYTE	0x03	/* Set target to value */
+#define MMC_SET_BLOCKLEN	16  /* ac [31:0] block len R1 */
 #define MMC_READ_MULTIPLE_BLOCK  18   /* adtc [31:0] data addr   R1  */
 #define MMC_SET_BLOCK_COUNT      23   /* adtc [31:0] data addr   R1  */
 #define MMC_WRITE_BLOCK		24	/* adtc [31:0] data addr	R1  */
@@ -46,6 +47,7 @@
 					      [1] Discard Enable
 					      [0] Identify Write Blocks for
 					      Erase (or TRIM Enable)  R1b */
+#define MMC_LOCK_UNLOCK		42  /* adtc R1b */
 #define MMC_GEN_CMD		56   /* adtc  [31:1] stuff bits.
 					      [0]: RD/WR1 R1 */
 
@@ -70,6 +72,15 @@
 #define R1_EXCEPTION_EVENT      (1 << 6)        /* sr, a */
 #define R1_APP_CMD              (1 << 5)        /* sr, c */
 
+#define MMC_CMD42_UNLOCK	0x0 /* UNLOCK */
+#define MMC_CMD42_SET_PWD	0x1 /* SET_PWD */
+#define MMC_CMD42_CLR_PWD	0x2 /* CLR_PWD */
+#define MMC_CMD42_LOCK		0x4 /* LOCK */
+#define MMC_CMD42_SET_LOCK	0x5 /* SET_PWD & LOCK */
+#define MMC_CMD42_ERASE		0x8 /* ERASE */
+#define MAX_PWD_LENGTH		32 /* max PWDS_LEN: old+new */
+#define MMC_BLOCK_SIZE		512 /* data blk size for cmd42 */
+
 /*
  * EXT_CSD fields
  */
diff --git a/mmc_cmds.c b/mmc_cmds.c
index 936e0c5..03fe04f 100644
--- a/mmc_cmds.c
+++ b/mmc_cmds.c
@@ -129,6 +129,129 @@ int send_status(int fd, __u32 *response)
 	return ret;
 }
 
+//lock/unlock feature implementation
+int do_lock_unlock(int nargs, char **argv)
+{
+	int fd, ret = 0;
+	char *device;
+	__u8 data_block[MMC_BLOCK_SIZE]={0};
+	__u8 data_block_onebyte[1]={0};
+	int block_size = 0;
+	struct mmc_ioc_cmd idata;
+	int cmd42_para;			//parameter of cmd42
+	char pwd[MAX_PWD_LENGTH+1];	//password
+	int pwd_len;			//password length
+	__u32 r1_response;		//R1 response token
+
+	if (nargs != 4){
+		fprintf(stderr, "Usage: mmc cmd42 <password> <s|c|l|u|e> <device>\n");
+		exit(1);
+	}
+
+	strcpy(pwd, argv[1]);
+	pwd_len = strlen(pwd);
+
+	if (!strcmp("s", argv[2])) {
+		cmd42_para = MMC_CMD42_SET_PWD;
+		printf("Set password: password=%s ...\n", pwd);
+	}
+	else if (!strcmp("c", argv[2])) {
+		cmd42_para = MMC_CMD42_CLR_PWD;
+		printf("Clear password: password=%s ...\n", pwd);
+	}
+	else if (!strcmp("l", argv[2])) {
+		cmd42_para = MMC_CMD42_LOCK;
+		printf("Lock the card: password=%s ...\n", pwd);
+	}
+	else if (!strcmp("sl", argv[2])) {
+		cmd42_para = MMC_CMD42_SET_LOCK;
+		printf("Set password and lock the card: password - %s ...\n", pwd);
+	}
+	else if (!strcmp("u", argv[2])) {
+		cmd42_para = MMC_CMD42_UNLOCK;
+		printf("Unlock the card: password=%s ...\n", pwd);
+	}
+	else if (!strcmp("e", argv[2])) {
+		cmd42_para = MMC_CMD42_ERASE;
+		printf("Force erase ... (Warning: all card data will be erased together with PWD!)\n");
+	}
+	else {
+		printf("Invalid parameter:\n" "s\tset password\n" "c\tclear password\n" "l\tlock\n"
+			"sl\tset password and lock\n" "u\tunlock\n" "e\tforce erase\n");
+		exit(1);
+	}
+
+	device = argv[nargs-1];
+
+	fd = open(device, O_RDWR);
+	if (fd < 0) {
+		perror("open");
+		exit(1);
+	}
+
+	if (cmd42_para==MMC_CMD42_ERASE)
+		block_size = 2; //set blk size to 2-byte for Force Erase @DDR50 compability
+	else
+		block_size = MMC_BLOCK_SIZE;
+
+	ret = set_block_len(fd, block_size); //set data block size prior to cmd42
+	printf("Set to data block length = %d byte(s).\n", block_size);
+
+	if (cmd42_para==MMC_CMD42_ERASE) {
+		data_block_onebyte[0] = cmd42_para;
+	} else {
+		data_block[0] = cmd42_para;
+		data_block[1] = pwd_len;
+		memcpy((char *)(data_block+2), pwd, pwd_len);
+	}
+
+	memset(&idata, 0, sizeof(idata));
+	idata.write_flag = 1;
+	idata.opcode = MMC_LOCK_UNLOCK;
+	idata.arg = 0;		//set all 0 for cmd42 arg
+	idata.flags = MMC_RSP_R1 | MMC_CMD_AC | MMC_CMD_ADTC;
+	idata.blksz = block_size;
+	idata.blocks = 1;
+
+	if (cmd42_para==MMC_CMD42_ERASE)
+		mmc_ioc_cmd_set_data(idata, data_block_onebyte);
+	else
+		mmc_ioc_cmd_set_data(idata, data_block);
+
+	ret = ioctl(fd, MMC_IOC_CMD, &idata);		//Issue CMD42
+
+	r1_response = idata.response[0];
+	printf("cmd42 response: 0x%08x\n", r1_response);
+	if (r1_response & R1_ERROR) {		//check CMD42 error
+		printf("cmd42 error! Error code: 0x%08x\n", r1_response & R1_ERROR);
+		ret=-1;
+	}
+	if (r1_response & R1_LOCK_UNLOCK_FAILED) {	//check lock/unlock error
+		printf("Card lock/unlock fail! Error code: 0x%08x\n",
+		r1_response & R1_LOCK_UNLOCK_FAILED);
+		ret=-1;
+	}
+
+	close(fd);
+	return ret;
+}
+
+//change data block length
+int set_block_len(int fd, int blk_len)
+{
+	int ret = 0;
+	struct mmc_ioc_cmd idata;
+
+	memset(&idata, 0, sizeof(idata));
+	idata.opcode = MMC_SET_BLOCKLEN;
+	idata.arg = blk_len;
+	idata.flags = MMC_RSP_R1 | MMC_CMD_AC;
+
+	ret = ioctl(fd, MMC_IOC_CMD, &idata);
+
+	return ret;
+}
+
 static __u32 get_size_in_blks(int fd)
 {
 	int res;
diff --git a/mmc_cmds.h b/mmc_cmds.h
index 5f2bef1..9ee78a2 100644
--- a/mmc_cmds.h
+++ b/mmc_cmds.h
@@ -50,3 +50,5 @@ int do_general_cmd_read(int nargs, char **argv);
 int do_softreset(int nargs, char **argv);
 int do_preidle(int nargs, char **argv);
 int do_alt_boot_op(int nargs, char **argv);
+int do_lock_unlock(int nargs, char **argv);
+int set_block_len(int fd, int blk_len);
