X509_ATTRIBUTE(3)

NAME
X509_ATTRIBUTE, X509at_get_attr, X509at_get_attr_count, X509at_get_attr_by_NID, X509at_get_attr_by_OBJ, X509at_delete_attr, X509at_add1_attr, X509at_add1_attr_by_OBJ, X509at_add1_attr_by_NID, X509at_add1_attr_by_txt, X509at_get0_data_by_OBJ, X509_ATTRIBUTE_create, X509_ATTRIBUTE_create_by_NID, X509_ATTRIBUTE_create_by_OBJ, X509_ATTRIBUTE_create_by_txt, X509_ATTRIBUTE_set1_object, X509_ATTRIBUTE_set1_data, X509_ATTRIBUTE_count, X509_ATTRIBUTE_get0_data, X509_ATTRIBUTE_get0_object, X509_ATTRIBUTE_get0_type - X509 attribute functions

SYNOPSIS
 #include <openssl/x509.h>

 typedef struct x509_attributes_st X509_ATTRIBUTE;

 int X509at_get_attr_count(const STACK_OF(X509_ATTRIBUTE) *x);
 int X509at_get_attr_by_NID(const STACK_OF(X509_ATTRIBUTE) *x, int nid,
                            int lastpos);
 int X509at_get_attr_by_OBJ(const STACK_OF(X509_ATTRIBUTE) *sk,
                            const ASN1_OBJECT *obj, int lastpos);
 X509_ATTRIBUTE *X509at_get_attr(const STACK_OF(X509_ATTRIBUTE) *x, int loc);
 X509_ATTRIBUTE *X509at_delete_attr(STACK_OF(X509_ATTRIBUTE) *x, int loc);
 STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr(STACK_OF(X509_ATTRIBUTE) **x,
                                            X509_ATTRIBUTE *attr);
 STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr_by_OBJ(STACK_OF(X509_ATTRIBUTE)
                                                   **x, const ASN1_OBJECT *obj,
                                                   int type,
                                                   const unsigned char *bytes,
                                                   int len);
 STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr_by_NID(STACK_OF(X509_ATTRIBUTE)
                                                   **x, int nid, int type,
                                                   const unsigned char *bytes,
                                                   int len);
 STACK_OF(X509_ATTRIBUTE) *X509at_add1_attr_by_txt(STACK_OF(X509_ATTRIBUTE)
                                                   **x, const char *attrname,
                                                   int type,
                                                   const unsigned char *bytes,
                                                   int len);
 void *X509at_get0_data_by_OBJ(const STACK_OF(X509_ATTRIBUTE) *x,
                               const ASN1_OBJECT *obj, int lastpos, int type);
 X509_ATTRIBUTE *X509_ATTRIBUTE_create(int nid, int atrtype, void *value);
 X509_ATTRIBUTE *X509_ATTRIBUTE_create_by_NID(X509_ATTRIBUTE **attr, int nid,
                                              int atrtype, const void *data,
                                              int len);
 X509_ATTRIBUTE *X509_ATTRIBUTE_create_by_OBJ(X509_ATTRIBUTE **attr,
                                              const ASN1_OBJECT *obj,
                                              int atrtype, const void *data,
                                              int len);
 X509_ATTRIBUTE *X509_ATTRIBUTE_create_by_txt(X509_ATTRIBUTE **attr,
                                              const char *atrname, int type,
                                              const unsigned char *bytes,
                                              int len);
 int X509_ATTRIBUTE_set1_object(X509_ATTRIBUTE *attr, const ASN1_OBJECT *obj);
 int X509_ATTRIBUTE_set1_data(X509_ATTRIBUTE *attr, int attrtype,
                              const void *data, int len);
 const void *X509_ATTRIBUTE_get0_data(const X509_ATTRIBUTE *attr, int idx,
                                      int atrtype, void *data);
 int X509_ATTRIBUTE_count(const X509_ATTRIBUTE *attr);
 const ASN1_OBJECT *X509_ATTRIBUTE_get0_object(const X509_ATTRIBUTE *attr);
 const ASN1_TYPE *X509_ATTRIBUTE_get0_type(const X509_ATTRIBUTE *attr, int idx);

DESCRIPTION
X509_ATTRIBUTE objects are used by many standards including X509, X509_REQ, PKCS12, PKCS8, PKCS7 and CMS.

The X509_ATTRIBUTE object is used to represent the ASN.1 Attribute as defined in RFC 5280, i.e.

 Attribute ::= SEQUENCE {
   type             AttributeType,
   values    SET OF AttributeValue }

 AttributeType ::= OBJECT IDENTIFIER
 AttributeValue ::= ANY -- DEFINED BY AttributeType

For example CMS defines the signing-time attribute as:

  id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
      us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }

  SigningTime ::= Time

  Time ::= CHOICE {
    utcTime UTCTime,
    generalizedTime GeneralizedTime }

In OpenSSL AttributeType maps to an ASN1_OBJECT object and AttributeValue maps to a list of ASN1_TYPE objects.

The following functions are used for X509_ATTRIBUTE objects.

X509at_get_attr_by_OBJ() finds the location of the first matching object obj in a list of attributes sk. The search starts at the position after lastpos. If the returned value is positive then it can be used on the next call to X509at_get_attr_by_OBJ() as the value of lastpos in order to iterate through the remaining attributes. lastpos can be set to any negative value on the first call, in order to start searching from the start of the list.

X509at_get_attr_by_NID() is similar to X509at_get_attr_by_OBJ() except that it passes the numerical identifier (NID) nid associated with the object. See <openssl/obj_mac.h> for a list of NID_*.

X509at_get_attr() returns the X509_ATTRIBUTE object at index loc in the list of attributes x. loc should be in the range from 0 to X509at_get_attr_count() - 1.

X509at_delete_attr() removes the X509_ATTRIBUTE object at index loc in the list of attributes x.

X509at_add1_attr() pushes a copy of the passed in X509_ATTRIBUTE object to the list x. Both x and attr must be non NULL or an error will occur. If *x is NULL then a new list is created, otherwise it uses the passed in list. An error will occur if an existing attribute (with the same attribute type) already exists in the attribute list.

X509at_add1_attr_by_OBJ() creates a new X509_ATTRIBUTE using X509_ATTRIBUTE_set1_object() and X509_ATTRIBUTE_set1_data() to assign a new obj with type type and data bytes of length len and then pushes it to the attribute list x. Both x and attr must be non NULL or an error will occur. If *x is NULL then a new attribute list is created. If obj already exists in the attribute list then an error occurs.

X509at_add1_attr_by_NID() is similar to X509at_add1_attr_by_OBJ() except that it passes the numerical identifier (NID) nid associated with the object. See <openssl/obj_mac.h> for a list of NID_*.

X509at_add1_attr_by_txt() is similar to X509at_add1_attr_by_OBJ() except that it passes a name attrname associated with the object. See <openssl/obj_mac.h> for a list of SN_* names.

X509_ATTRIBUTE_set1_object() assigns a ASN1_OBJECT obj to the attribute attr. If attr contained an existing ASN1_OBJECT then it is freed. An error occurs if either attr or obj are NULL, or if the passed in obj cannot be duplicated.

X509_ATTRIBUTE_set1_data() pushes a new ASN1_TYPE object onto the attr attributes list. The new object is assigned a copy of the data in data of size len. If attrtype has flag MBSTRING_FLAG set then a table lookup using the attr attributes NID is used to set an ASN1_STRING using ASN1_STRING_set_by_NID(), and the passed in data must be in the format required for that object type or an error will occur. If len is not -1 then internally ASN1_STRING_type_new() is used with the passed in attrtype. If attrtype is 0 the call does nothing except return 1.

X509_ATTRIBUTE_create() creates a new X509_ATTRIBUTE using the nid to set the ASN1_OBJECT OID and the atrtype and value to set the ASN1_TYPE.

X509_ATTRIBUTE_create_by_OBJ() uses X509_ATTRIBUTE_set1_object() and X509_ATTRIBUTE_set1_data() to assign a new obj with type atrtype and data data of length len. If the passed in attribute attr OR *attr is NULL then a new X509_ATTRIBUTE will be returned, otherwise the passed in X509_ATTRIBUTE is used. Note that the ASN1_OBJECT obj is pushed onto the attributes existing list of objects, which could be an issue if the attributes <ASN1_OBJECT> was different.

X509_ATTRIBUTE_create_by_NID() is similar to X509_ATTRIBUTE_create_by_OBJ() except that it passes the numerical identifier (NID) nid associated with the object. See <openssl/obj_mac.h> for a list of NID_*.

X509_ATTRIBUTE_create_by_txt() is similar to X509_ATTRIBUTE_create_by_OBJ() except that it passes a name atrname associated with the object. See <openssl/obj_mac.h> for a list of SN_* names.

X509_ATTRIBUTE_count() returns the number of ASN1_TYPE objects in an attribute attr.

X509_ATTRIBUTE_get0_type() returns the ASN1_TYPE object at index idx in the attribute list attr. idx should be in the range of 0 to X509_ATTRIBUTE_count() - 1 or an error will occur.

X509_ATTRIBUTE_get0_data() returns the data of an ASN1_TYPE object at index idx in the attribute attr. data is unused and can be set to NULL. An error will occur if the attribute type atrtype does not match the type of the ASN1_TYPE object at index idx OR if atrtype is either V_ASN1_BOOLEAN or V_ASN1_NULL OR if the idx is not in the range 0 to X509_ATTRIBUTE_count() - 1.

X509at_get0_data_by_OBJ() finds the first attribute in an attribute list x that matches the obj starting at index lastpos and returns the data retrieved from the found attributes first ASN1_TYPE object. An error will occur if the attribute type type does not match the type of the ASN1_TYPE object OR if type is either V_ASN1_BOOLEAN or V_ASN1_NULL OR the attribute is not found. If lastpos is less than -1 then an error will occur if there are multiple objects in the list x that match obj. If lastpos is less than -2 then an error will occur if there is more than one ASN1_TYPE object in the found attribute.

RETURN VALUES
X509at_get_attr_count() returns the number of attributes in the list x or -1 if x is NULL.

X509at_get_attr_by_OBJ() returns -1 if either the list is empty OR the object is not found, otherwise it returns the location of the object in the list.

X509at_get_attr_by_NID() is similar to X509at_get_attr_by_OBJ(), except that it returns -2 if the nid is not known by OpenSSL.

X509at_get_attr() returns either an X509_ATTRIBUTE or NULL if there is a error.

X509at_delete_attr() returns either the removed X509_ATTRIBUTE or NULL if there is a error.

X509_ATTRIBUTE_count() returns -1 on error, otherwise it returns the number of ASN1_TYPE elements.

X509_ATTRIBUTE_get0_type() returns NULL on error, otherwise it returns a ASN1_TYPE object.

X509_ATTRIBUTE_get0_data() returns NULL if an error occurs, otherwise it returns the data associated with an ASN1_TYPE object.

X509_ATTRIBUTE_set1_object() and X509_ATTRIBUTE_set1_data() returns 1 on success, or 0 otherwise.

X509_ATTRIBUTE_create(), X509_ATTRIBUTE_create_by_OBJ(), X509_ATTRIBUTE_create_by_NID() and X509_ATTRIBUTE_create_by_txt() return either a X509_ATTRIBUTE on success, or NULL if there is a error.

X509at_add1_attr(), X509at_add1_attr_by_OBJ(), X509at_add1_attr_by_NID() and X509at_add1_attr_by_txt() return NULL on error, otherwise they return a list of X509_ATTRIBUTE.

X509at_get0_data_by_OBJ() returns the data retrieved from the found attributes first ASN1_TYPE object, or NULL if an error occurs.

SEE ALSO
ASN1_TYPE_get(3), ASN1_INTEGER_get(3), ASN1_ENUMERATED_get(3), ASN1_STRING_get0_data(3), ASN1_STRING_length(3), ASN1_STRING_type(3), X509_REQ_get_attr(3), EVP_PKEY_get_attr(3), CMS_signed_get_attr(3), PKCS8_pkey_get0_attrs(3),

COPYRIGHT
Copyright 2023-2026 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.