diff --git a/include/iscsi-private.h b/include/iscsi-private.h
index 6bd72a4..1fce36a 100644
--- a/include/iscsi-private.h
+++ b/include/iscsi-private.h
@@ -98,7 +98,7 @@ struct iscsi_in_pdu {
 void iscsi_free_iscsi_in_pdu(struct iscsi_context *iscsi, struct iscsi_in_pdu *in);
 
 /* size of chap response field */
-#define MAX_CHAP_R_SIZE 20 /* md5:16  sha1:20 */
+#define MAX_CHAP_R_SIZE 32 /* md5:16  sha1:20 */
 
 /* max length of chap challange */
 #define MAX_CHAP_C_LENGTH 2048
@@ -124,7 +124,7 @@ struct iscsi_context {
 	char target_user[MAX_STRING_SIZE+1];
 	char target_passwd[MAX_STRING_SIZE+1];
 	int target_chap_i;
-	char target_chap_r[MAX_CHAP_R_SIZE];
+	unsigned char target_chap_r[MAX_CHAP_R_SIZE];
 
 	char error_string[MAX_STRING_SIZE+1];
 
diff --git a/lib/login.c b/lib/login.c
index 120c8c2..0dbe3de 100644
--- a/lib/login.c
+++ b/lib/login.c
@@ -936,8 +936,9 @@ iscsi_login_add_chap_response(struct iscsi_context *iscsi, struct iscsi_pdu *pdu
 
 	/* bidirectional chap */
 	if (iscsi->target_user[0]) {
-		char target_chap_c[MAX_CHAP_R_SIZE * 2];
-
+		char target_chap_c[MAX_CHAP_R_SIZE * 2] = {0};
+		char target_chap_c_hex[MAX_CHAP_R_SIZE * 4 + 1] = { 0 };
+		
 		iscsi->target_chap_i++;
 		snprintf(str, MAX_STRING_SIZE, "CHAP_I=%d",
 			 iscsi->target_chap_i);
@@ -962,6 +963,7 @@ iscsi_login_add_chap_response(struct iscsi_context *iscsi, struct iscsi_pdu *pdu
 			c = target_chap_c[i];
 			cc[0] = i2h((c >> 4)&0x0f);
 			cc[1] = i2h((c     )&0x0f);
+			memcpy(target_chap_c_hex + i * 2, cc, 2);
 			if (iscsi_pdu_add_data(iscsi, pdu, &cc[0], 2) != 0) {
 				iscsi_set_error(iscsi, "Out-of-memory: pdu add "
 						"data failed.");
@@ -977,7 +979,7 @@ iscsi_login_add_chap_response(struct iscsi_context *iscsi, struct iscsi_pdu *pdu
 
                 compute_chap_r(iscsi, iscsi->target_chap_i,
                                (unsigned char *)iscsi->target_passwd,
-                               (unsigned char *)target_chap_c,
+                               (unsigned char *)target_chap_c_hex,
                                (unsigned char *)iscsi->target_chap_r);
 	}