X509_ATTRIBUTE_SET1_OBJECT(3) | Library Functions Manual | X509_ATTRIBUTE_SET1_OBJECT(3)

# NAME

`X509_ATTRIBUTE_set1_object`, `X509_ATTRIBUTE_set1_data`, `X509_ATTRIBUTE_create_by_OBJ`, `X509_ATTRIBUTE_create_by_NID`, `X509_ATTRIBUTE_create_by_txt` — modify an X.501 Attribute

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509.h>`

int
`X509_ATTRIBUTE_set1_object`(X509_ATTRIBUTE *attr, const ASN1_OBJECT *obj);

int
`X509_ATTRIBUTE_set1_data`(X509_ATTRIBUTE *attr, int type, const void *data, int len);

X509_ATTRIBUTE *
`X509_ATTRIBUTE_create_by_OBJ`(X509_ATTRIBUTE **pattr, const ASN1_OBJECT *obj, int type, const void *data, int len);

X509_ATTRIBUTE *
`X509_ATTRIBUTE_create_by_NID`(X509_ATTRIBUTE **pattr, int nid, int type, const void *data, int len);

X509_ATTRIBUTE *
`X509_ATTRIBUTE_create_by_txt`(X509_ATTRIBUTE **pattr, const char *name, int type, const unsigned char *data, int len);

# DESCRIPTION

`X509_ATTRIBUTE_set1_object`() sets the type of attr to obj. If obj is dynamically allocated, a deep copy is created. If the type of attr was already set, the old type is freed as far as it was dynamically allocated. After calling this function, attr may be in an inconsistent state because its values may not agree with the new attribute type.

`X509_ATTRIBUTE_set1_data`() sets attr to be multi-valued and initializes its set of values to contain a single new ASN.1 ANY object representing the data.

The interpretation of the data depends on the values of the type and len arguments; there are four different cases.

If the type argument has the bit `MBSTRING_FLAG` set, data is expected to point to a multibyte character string that is len bytes long and uses the encoding specified by the type argument, and it is expected that an attribute type was already assigned to attr, for example by calling `X509_ATTRIBUTE_set1_object`() before calling `X509_ATTRIBUTE_set1_data`(). In this case, an appropriate ASN.1 multibyte string type is chosen and a new object of that type is allocated and populated to represent the data by calling ASN1_STRING_set_by_NID(3). The type of that new ASN.1 string object is subsequently used instead of the type argument.

If the type argument does not have the bit `MBSTRING_FLAG` set and the len argument is not -1, the type argument is expected to be one of the types documented in ASN1_STRING_new(3) and data is expected to point to a buffer of len bytes. In this case, a new object is allocated with ASN1_STRING_type_new(3) and populated with ASN1_STRING_set(3).

If the type argument does not have the bit `MBSTRING_FLAG` set and the len argument is -1, data is expected to point to an object of the given type rather than to a buffer. In this case, a deep copy of the existing object into the new ASN.1 ANY object is performed with ASN1_TYPE_set1(3).

If the type argument is 0, the data and len arguments are ignored and the set of values is left empty instead of adding a single ASN.1 ANY object to it. This violates section 8.2 of the X.501 standard, which requires every attribute to contain at least one value, but some attribute types used by the library use empty sets of values anyway.

`X509_ATTRIBUTE_create_by_OBJ`() sets the type of **attr to obj using `X509_ATTRIBUTE_set1_object`() and copies the data into it using `X509_ATTRIBUTE_set1_data`(). If attr or *attr is `NULL`, a new X509_ATTRIBUTE object is allocated, populated, and returned.

`X509_ATTRIBUTE_create_by_NID`() is a wrapper around `X509_ATTRIBUTE_create_by_OBJ`() that obtains the required obj argument by calling OBJ_nid2obj(3) on the nid argument.

`X509_ATTRIBUTE_create_by_txt`() is a similar wrapper that obtains obj by calling OBJ_txt2obj(3) with the arguments name and 0, which means that long names, short names, and numerical OID strings are all acceptable.

# RETURN VALUES

`X509_ATTRIBUTE_set1_object`() returns 1 if successful or 0 if attr or obj is `NULL` or if memory allocation fails.

`X509_ATTRIBUTE_set1_data`() returns 1 if successful or 0 if attr is `NULL` or if ASN1_STRING_set_by_NID(3), ASN1_STRING_set(3), ASN1_TYPE_set1(3), or memory allocation fails.

`X509_ATTRIBUTE_create_by_OBJ`(), `X509_ATTRIBUTE_create_by_NID`(), and `X509_ATTRIBUTE_create_by_txt`() return a pointer to the changed or new object or `NULL` if obtaining obj, allocating memory, or copying fails.

# SEE ALSO

ASN1_OBJECT_new(3), ASN1_STRING_new(3), ASN1_STRING_set(3), ASN1_STRING_set_by_NID(3), ASN1_TYPE_new(3), OBJ_nid2obj(3), X509_ATTRIBUTE_get0_object(3), X509_ATTRIBUTE_new(3)

# HISTORY

These functions first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.

# BUGS

If attr already contains one or more values, `X509_ATTRIBUTE_set1_data`(), `X509_ATTRIBUTE_create_by_OBJ`(), `X509_ATTRIBUTE_create_by_NID`(), and `X509_ATTRIBUTE_create_by_txt`() silently overwrite the pointers to the old values and leak the memory used for them.

June 8, 2025 | Debian