diff --git a/include/gmssl/asn1.h b/include/gmssl/asn1.h
index 307fc646..49c0b0b7 100644
--- a/include/gmssl/asn1.h
+++ b/include/gmssl/asn1.h
@@ -69,42 +69,6 @@ enum ASN1_TAG {
 };
 
 
-/*
-DER encoding (d, dlen) to_der
-
-	d != NULL && dlen != 0: return 1 on success or -1 on failure
-	d == NULL && dlen != 0: invalid input, return -1
-	d == NULL && dlen == 0: do nothing, return 0 to info OPTIONAL types
-	d != NULL && dlen == 0: encode an empty type, output tag and length = 0 without value
-
-解码函数的返回值：
-
-	ret == 0
-		当前剩余的数据数据长度为0
-		或者下一个对象与期待不符，即输入对象的标签不等于输入的tag
-		当对象为OPTIONAL时，调用方可以通过判断返回值是否为0进行处理
-	ret < 0
-		标签正确但是长度或数据解析出错
-	ret == 1
-		解析正确
-
-
-解码函数的输入：
-
-	*in != NULL
-		例如一个SEQUENCE中的属性均为OPTIONAL，解析后指针仍不为空
-		因此不允许输入空的输入数据指针
-
-
-处理规则
-
-	当返回值 ret <= 0 时，*tag, *in, *inlen 的值保持不变
-
-	如果一个类型有 DEFAULT 属性，调用方可以将返回数据预先设置为默认值，
-	如果该对象未被编码，即返回值为0，那么解码函数不会修改已经设置的默认值
-
-*/
-
 const char *asn1_tag_name(int tag);
 int asn1_tag_is_cstring(int tag);
 int asn1_tag_to_der(int tag, uint8_t **out, size_t *outlen);
@@ -293,8 +257,8 @@ int asn1_sequence_of_int_print(FILE *fp, int fmt, int ind, const char *label, co
 
 #define asn1_set_to_der(d,dlen,out,outlen) asn1_nonempty_type_to_der(ASN1_TAG_SET,d,dlen,out,outlen)
 #define asn1_set_from_der(d,dlen,in,inlen) asn1_nonempty_type_from_der(ASN1_TAG_SET,d,dlen,in,inlen)
-#define asn1_implicit_set_to_der(i,d,dlen,out,outlen) asn1_nonempty_type_to_der(ASN1_TAG_EXPLICIT(i),d,dlen,out,outlen)
-#define asn1_implicit_set_from_der(i,d,dlen,in,inlen) asn1_nonempty_type_from_der(ASN1_TAG_EXPLICIT(i),d,dlen,in,inlen)
+#define asn1_implicit_set_to_der(i,d,dlen,out,outlen) asn1_type_to_der(ASN1_TAG_EXPLICIT(i),d,dlen,out,outlen)
+#define asn1_implicit_set_from_der(i,d,dlen,in,inlen) asn1_type_from_der(ASN1_TAG_EXPLICIT(i),d,dlen,in,inlen)
 
 #define asn1_set_of_to_der(d,dlen,out,outlen) asn1_nonempty_type_to_der(ASN1_TAG_SET,d,dlen,out,outlen)
 #define asn1_set_of_from_der(d,dlen,in,inlen) asn1_nonempty_type_from_der(ASN1_TAG_SET,d,dlen,in,inlen)
diff --git a/src/x509_cer.c b/src/x509_cer.c
index c77ef0b2..5cfe2b48 100644
--- a/src/x509_cer.c
+++ b/src/x509_cer.c
@@ -647,7 +647,7 @@ int x509_name_add_country_name(uint8_t *d, size_t *dlen, size_t maxlen, const ch
 {
 	int ret;
 	ret = x509_name_add_rdn(d, dlen, maxlen,
-		OID_at_country_name, ASN1_TAG_PrintableString, (uint8_t *)val, 2, NULL, 0);
+		OID_at_country_name, ASN1_TAG_PrintableString, (uint8_t *)val, val ? 2 : 0, NULL, 0);
 	if (ret < 0) error_print();
 	return ret;
 }
diff --git a/src/x509_ext.c b/src/x509_ext.c
index 5aa2700f..f2e1476c 100644
--- a/src/x509_ext.c
+++ b/src/x509_ext.c
@@ -1762,6 +1762,9 @@ int x509_attributes_print(FILE *fp, int fmt, int ind, const char *label, const u
 		format_print(fp, fmt, ind, "%s\n", label);
 		ind += 4;
 	}
+	if (!dlen) {
+		format_print(fp, fmt, ind, "(null)\n");
+	}
 	while (dlen) {
 		if (asn1_sequence_from_der(&p, &len, &d, &dlen) != 1) {
 			error_print();
diff --git a/src/x509_req.c b/src/x509_req.c
index e39aad53..91fb30ba 100644
--- a/src/x509_req.c
+++ b/src/x509_req.c
@@ -41,12 +41,12 @@ int x509_request_info_to_der(
 	if (asn1_int_to_der(version, NULL, &len) != 1
 		|| asn1_sequence_to_der(subject, subject_len, NULL, &len) != 1
 		|| x509_public_key_info_to_der(subject_public_key, NULL, &len) != 1
-		|| asn1_implicit_set_to_der(0, attrs, attrs_len, NULL, &len) < 0
+		|| asn1_implicit_set_to_der(0, attrs, attrs_len, NULL, &len) != 1
 		|| asn1_sequence_header_to_der(len, out, outlen) != 1
 		|| asn1_int_to_der(version, out, outlen) != 1
 		|| asn1_sequence_to_der(subject, subject_len, out, outlen) != 1
 		|| x509_public_key_info_to_der(subject_public_key, out, outlen) != 1
-		|| asn1_implicit_set_to_der(0, attrs, attrs_len, out, outlen) < 0) {
+		|| asn1_implicit_set_to_der(0, attrs, attrs_len, out, outlen) != 1) {
 		error_print();
 		return -1;
 	}
diff --git a/tools/reqgen.c b/tools/reqgen.c
index 226de63e..2aeffa66 100644
--- a/tools/reqgen.c
+++ b/tools/reqgen.c
@@ -72,6 +72,10 @@ int reqgen_main(int argc, char **argv)
 	char *org_unit = NULL;
 	char *common_name = NULL;
 
+	// Attributs
+	uint8_t attrs[512];
+	size_t attrs_len = 0;
+
 	// Private Key
 	FILE *keyfp = NULL;
 	char *pass = NULL;
@@ -203,7 +207,7 @@ bad:
 		X509_version_v1,
 		name, namelen,
 		&sm2_key,
-		NULL, 0,
+		attrs, attrs_len,
 		OID_sm2sign_with_sm3,
 		&sm2_key, signer_id, signer_id_len,
 		&p, &reqlen) != 1) {