.\"	$OpenBSD: OBJ_nid2obj.3,v 1.4 2016/11/27 18:22:25 schwarze Exp $
.\"	OpenSSL c264592d May 14 11:28:00 2006 +0000
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.Dd $Mdocdate: November 27 2016 $
.Dt OBJ_NID2OBJ 3
.Os
.Sh NAME
.Nm OBJ_nid2obj ,
.Nm OBJ_nid2ln ,
.Nm OBJ_nid2sn ,
.Nm OBJ_obj2nid ,
.Nm OBJ_ln2nid ,
.Nm OBJ_sn2nid ,
.Nm OBJ_txt2nid ,
.Nm OBJ_txt2obj ,
.Nm OBJ_obj2txt ,
.Nm OBJ_cmp ,
.Nm OBJ_dup ,
.Nm OBJ_create ,
.Nm OBJ_cleanup ,
.Nm i2t_ASN1_OBJECT
.Nd ASN.1 object utility functions
.Sh SYNOPSIS
.In openssl/objects.h
.Ft ASN1_OBJECT *
.Fo OBJ_nid2obj
.Fa "int n"
.Fc
.Ft const char *
.Fo OBJ_nid2ln
.Fa "int n"
.Fc
.Ft const char *
.Fo OBJ_nid2sn
.Fa "int n"
.Fc
.Ft int
.Fo OBJ_obj2nid
.Fa "const ASN1_OBJECT *o"
.Fc
.Ft int
.Fo OBJ_ln2nid
.Fa "const char *ln"
.Fc
.Ft int
.Fo OBJ_sn2nid
.Fa "const char *sn"
.Fc
.Ft int
.Fo OBJ_txt2nid
.Fa "const char *s"
.Fc
.Ft ASN1_OBJECT *
.Fo OBJ_txt2obj
.Fa "const char *s"
.Fa "int no_name"
.Fc
.Ft int
.Fo OBJ_obj2txt
.Fa "char *buf"
.Fa "int buf_len"
.Fa "const ASN1_OBJECT *a"
.Fa "int no_name"
.Fc
.Ft int
.Fo OBJ_cmp
.Fa "const ASN1_OBJECT *a"
.Fa "const ASN1_OBJECT *b"
.Fc
.Ft ASN1_OBJECT *
.Fo OBJ_dup
.Fa "const ASN1_OBJECT *o"
.Fc
.Ft int
.Fo OBJ_create
.Fa "const char *oid"
.Fa "const char *sn"
.Fa "const char *ln"
.Fc
.Ft void
.Fn OBJ_cleanup void
.In openssl/asn1.h
.Ft int
.Fo i2t_ASN1_OBJECT
.Fa "char *buf"
.Fa "int buf_len"
.Fa "ASN1_OBJECT *a"
.Fc
.Sh DESCRIPTION
The ASN.1 object utility functions process
.Vt ASN1_OBJECT
structures which are a representation of the ASN.1 OBJECT IDENTIFIER
(OID) type.
For convenience, OIDs are usually represented in source code as
numeric identifiers, or NIDs.
OpenSSL has an internal table of OIDs that are generated when the
library is built, and their corresponding NIDs are available as
defined constants.
For the functions below, application code should treat all returned
values \(em OIDs, NIDs, or names \(em as constants.
.Pp
.Fn OBJ_nid2obj ,
.Fn OBJ_nid2ln ,
and
.Fn OBJ_nid2sn
convert the NID
.Fa n
to an
.Vt ASN1_OBJECT
structure, its long name, and its short name, respectively, or return
.Dv NULL
if an error occurred.
.Pp
.Fn OBJ_obj2nid ,
.Fn OBJ_ln2nid ,
and
.Fn OBJ_sn2nid
return the corresponding NID for the object
.Fa o ,
the long name
.Fa ln ,
or the short name
.Fa sn ,
respectively, or
.Dv NID_undef
if an error occurred.
.Pp
.Fn OBJ_txt2nid
returns the NID corresponding to text string
.Fa s .
.Fa s
can be a long name, a short name, or the numerical representation
of an object.
.Pp
.Fn OBJ_txt2obj
converts the text string
.Fa s
into an
.Vt ASN1_OBJECT
structure.
If
.Fa no_name
is 0 then long names and short names will be interpreted as well as
numerical forms.
If
.Fa no_name
is 1 only the numerical form is acceptable.
.Pp
.Fn OBJ_obj2txt
converts the
.Vt ASN1_OBJECT
.Fa a
into a textual representation.
The representation is written as a NUL terminated string to
.Fa buf .
At most
.Fa buf_len
bytes are written, truncating the result if necessary.
The total amount of space required is returned.
If
.Fa no_name
is 0 and the object has a long or short name, then that will be used,
otherwise the numerical form will be used.
.Pp
.Fn i2t_ASN1_OBJECT
is the same as
.Fn OBJ_obj2txt
with
.Fa no_name
set to 0.
.Pp
.Fn OBJ_cmp
compares
.Fa a
to
.Fa b .
If the two are identical, 0 is returned.
.Pp
.Fn OBJ_dup
returns a copy of
.Fa o .
.Pp
.Fn OBJ_create
adds a new object to the internal table.
.Fa oid
is the numerical form of the object,
.Fa sn
the short name and
.Fa ln
the long name.
A new NID is returned for the created object.
.Pp
.Fn OBJ_cleanup
cleans up the internal object table: this should be called before
an application exits if any new objects were added using
.Fn OBJ_create .
.Pp
Objects can have a short name, a long name, and a numerical
identifier (NID) associated with them.
A standard set of objects is represented in an internal table.
The appropriate values are defined in the header file
.In openssl/objects.h .
.Pp
For example, the OID for commonName has the following definitions:
.Bd -literal
#define SN_commonName                   "CN"
#define LN_commonName                   "commonName"
#define NID_commonName                  13
.Ed
.Pp
New objects can be added by calling
.Fn OBJ_create .
.Pp
Table objects have certain advantages over other objects: for example
their NIDs can be used in a C language switch statement.
They are also static constant structures which are shared: that is there
is only a single constant structure for each table object.
.Pp
Objects which are not in the table have the NID value
.Dv NID_undef .
.Pp
Objects do not need to be in the internal tables to be processed:
the functions
.Fn OBJ_txt2obj
and
.Fn OBJ_obj2txt
can process the numerical form of an OID.
.Sh RETURN VALUES
.Fn OBJ_nid2obj
returns an
.Vt ASN1_OBJECT
structure or
.Dv NULL
if an error occurred.
.Pp
.Fn OBJ_nid2ln
and
.Fn OBJ_nid2sn
return a valid string or
.Dv NULL
on error.
.Pp
.Fn OBJ_obj2nid ,
.Fn OBJ_ln2nid ,
.Fn OBJ_sn2nid ,
and
.Fn OBJ_txt2nid
return a NID or
.Dv NID_undef
on error.
.Sh EXAMPLES
Create an object for
.Sy commonName :
.Bd -literal -offset indent
ASN1_OBJECT *o;
o = OBJ_nid2obj(NID_commonName);
.Ed
.Pp
Check if an object is
.Sy commonName :
.Bd -literal -offset indent
if (OBJ_obj2nid(obj) == NID_commonName)
	/* Do something */
.Ed
.Pp
Create a new NID and initialize an object from it:
.Bd -literal -offset indent
int new_nid;
ASN1_OBJECT *obj;
new_nid = OBJ_create("1.2.3.4", "NewOID", "New Object Identifier");
obj = OBJ_nid2obj(new_nid);
.Ed
.Pp
Create a new object directly:
.Bd -literal -offset indent
obj = OBJ_txt2obj("1.2.3.4", 1);
.Ed
.Sh SEE ALSO
.Xr ERR_get_error 3
.Sh BUGS
.Fn OBJ_obj2txt
is awkward and messy to use: it doesn't follow the convention of other
OpenSSL functions where the buffer can be set to
.Dv NULL
to determine the amount of data that should be written.
Instead
.Fa buf
must point to a valid buffer and
.Fa buf_len
should be set to a positive value.
A buffer length of 80 should be more than enough to handle any OID
encountered in practice.