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.\" Copyright (c) 2016, 2021 Ingo Schwarze <schwarze@openbsd.org>
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.Dd $Mdocdate: October 26 2021 $
.Dt X509_ATTRIBUTE_NEW 3
.Os
.Sh NAME
.Nm X509_ATTRIBUTE_new ,
.Nm X509_ATTRIBUTE_create ,
.Nm X509_ATTRIBUTE_dup ,
.Nm X509_ATTRIBUTE_free
.\" In the following line, "X.501" and "Attribute" are not typos.
.\" The "Attribute" type is defined in X.501, not in X.509.
.\" The type is called "Attribute" with capital "A", not "attribute".
.Nd generic X.501 Attribute
.Sh SYNOPSIS
.In openssl/x509.h
.Ft X509_ATTRIBUTE *
.Fn X509_ATTRIBUTE_new void
.Ft X509_ATTRIBUTE *
.Fn X509_ATTRIBUTE_create "int nid" "int type" "void *value"
.Ft X509_ATTRIBUTE *
.Fn X509_ATTRIBUTE_dup "X509_ATTRIBUTE *attr"
.Ft void
.Fn X509_ATTRIBUTE_free "X509_ATTRIBUTE *attr"
.Sh DESCRIPTION
In the X.501 standard, an
.Vt Attribute
is the fundamental ASN.1 data type used to represent any kind of
property of any kind of directory entry.
In OpenSSL, very few objects use it directly, most notably the
.Vt X509_REQ_INFO
object used for PKCS#10 certification requests described in
.Xr X509_REQ_new 3 ,
the
.Vt PKCS8_PRIV_KEY_INFO
object used for PKCS#8 private key information described in
.Xr PKCS8_PRIV_KEY_INFO_new 3 ,
and the
.Vt PKCS12_SAFEBAG
container object described in
.Xr PKCS12_SAFEBAG_new 3 .
.Pp
.Fn X509_ATTRIBUTE_new
allocates and initializes an empty
.Vt X509_ATTRIBUTE
object.
.Pp
.Fn X509_ATTRIBUTE_create
allocates a new multi-valued
.Vt X509_ATTRIBUTE
object of the type
.Fa nid
and initializes its set of values
to contain one new ASN.1 ANY object with the given
.Fa value
and
.Fa type .
The
.Fa type
usually is one of the
.Dv V_ASN1_*
constants defined in
.In openssl/asn1.h ;
it is stored without validating it.
If the function succeeds, ownership of the
.Fa value
is transferred to the new
.Vt X509_ATTRIBUTE
object.
.Pp
Be careful to not confuse the type of the attribute
and the type of the value.
.Pp
.Fn X509_ATTRIBUTE_dup
creates a deep copy of
.Fa attr .
.Pp
.Fn X509_ATTRIBUTE_free
frees
.Fa attr .
.Sh RETURN VALUES
.Fn X509_ATTRIBUTE_new ,
.Fn X509_ATTRIBUTE_create ,
and
.Fn X509_ATTRIBUTE_dup
return the new
.Vt X509_ATTRIBUTE
object or
.Dv NULL
if an error occurs.
.Pp
In particular, these functions fail if memory allocation fails.
.Fn X509_ATTRIBUTE_create
also fails if
.Xr OBJ_nid2obj 3
fails on
.Fa nid .
.Sh SEE ALSO
.Xr d2i_X509_ATTRIBUTE 3 ,
.Xr EVP_PKEY_add1_attr 3 ,
.Xr OBJ_nid2obj 3 ,
.Xr PKCS12_SAFEBAG_new 3 ,
.Xr PKCS7_add_attribute 3 ,
.Xr PKCS8_pkey_get0_attrs 3 ,
.Xr PKCS8_PRIV_KEY_INFO_new 3 ,
.Xr X509_ATTRIBUTE_get0_object 3 ,
.Xr X509_ATTRIBUTE_set1_object 3 ,
.Xr X509_EXTENSION_new 3 ,
.Xr X509_new 3 ,
.Xr X509_REQ_add1_attr 3 ,
.Xr X509_REQ_new 3 ,
.Xr X509at_add1_attr 3 ,
.Xr X509at_get_attr 3
.Sh STANDARDS
.Bl -ohang
.It Xo
For the general definition of the
.Vt Attribute
data type:
.Xc
ITU-T Recommendation X.501, also known as ISO/IEC 9594-2:
Information Technology \(en Open Systems Interconnection \(en
The Directory: Models, section 8.2: Overall structure
.It For the specific definition in the context of certification requests:
RFC 2986: PKCS #10: Certification Request Syntax Specification,
section 4.1: CertificationRequestInfo
.It For the specific use in the context of private key information:
RFC 5208: Public-Key Cryptography Standards (PKCS) #8:
Private-Key Information Syntax Specification
.It For the specific definition in the context of PFX:
RFC 7292: PKCS #12: Personal Information Exchange Syntax,
section 4.2: The SafeBag Type
.El
.Sh HISTORY
.Fn X509_ATTRIBUTE_new
and
.Fn X509_ATTRIBUTE_free
first appeared in SSLeay 0.5.1 and have been available since
.Ox 2.4 .
.Pp
.Fn X509_ATTRIBUTE_create
and
.Fn X509_ATTRIBUTE_dup
first appeared in SSLeay 0.9.1 and have been available since
.Ox 2.6 .
.Sh BUGS
A data type designed to hold arbitrary data is an oxymoron.
.Pp
While it may occasionally be useful for abstract syntax specification
or for generic container objects, using it for the representation
of specific data in a specific data structure feels like dubious
design.
.Pp
Having two distinct data types to hold arbitrary data \(en
in this case,
.Vt X509_ATTRIBUTE
on the X.501 language level and
.Vt X509_EXTENSION
as described in
.Xr X509_EXTENSION_new 3
on the X.509 language level \(en feels even more questionable,
in particular considering that Attributes in certification requests
can be used to ask for Extensions in certificates.
.Pp
At the very least, the direct use of the low-level generic
.Vt X509_ATTRIBUTE
type in specific data types like certification requests or private
key information looks like a layering violation and appears to put
type safety into jeopardy.