inspect and create ASN.1 object
const char *
const char *
OBJ_ln2nid(const char *ln);
OBJ_sn2nid(const char *sn);
OBJ_txt2nid(const char *s);
OBJ_txt2obj(const char *s,
int buf_len, const ASN1_OBJECT
*a, int no_name);
OBJ_cmp(const ASN1_OBJECT *a,
const ASN1_OBJECT *b);
int buf_len, const ASN1_OBJECT
const ASN1_OBJECT *a);
The ASN.1 object utility functions process 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 — OIDs, NIDs, or names — as constants.
convert the NID n to an
ASN1_OBJECT structure, its long name, and its short
name, respectively, or return
NULL if an error
return the corresponding NID for the object o, the
long name ln, or the short name
sn, respectively, or
if an error occurred.
returns the NID corresponding to text string s.
s can be a long name, a short name, or the numerical
representation of an object.
converts the text string s into an
ASN1_OBJECT structure. If
no_name is 0 then long names and short names will be
interpreted as well as numerical forms. If no_name is
1, only the numerical form is acceptable.
converts the ASN1_OBJECT a into
a textual representation. The representation is written as a NUL terminated
string to buf. At most buf_len
bytes are written, truncating the result if necessary. The total amount of
space required is returned. If 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.
is the same as
no_name set to 0.
writes a textual representation of a to
BIO_write(3). It does not write a terminating NUL byte. If
NULL or contains no data,
it writes the 4-byte string "NULL". If
i2a_ASN1_OBJECT() writes the 9-byte string
"<INVALID>". Otherwise, it writes the string constructed
compares a to b. If the two are
identical, 0 is returned.
returns a deep copy of o if o is
marked as dynamically allocated. The new object and all data contained in it
is marked as dynamically allocated. If o is not marked
as dynamically allocated,
OBJ_dup() just returns
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
For example, the OID for commonName has the following definitions:
#define SN_commonName "CN" #define LN_commonName "commonName" #define NID_commonName 13
New objects can be added by calling OBJ_create(3).
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.
Objects which are not in the table have the NID value
Objects do not need to be in the internal
tables to be processed: the functions
OBJ_obj2txt() can process the numerical form of
return an ASN1_OBJECT object or
NULL if an error occurs.
OBJ_nid2sn() return a valid string or
NULL on error.
OBJ_txt2nid() return a NID or
NID_undef on error.
i2t_ASN1_OBJECT() return the amount of space
required in bytes, including the terminating NUL byte.
i2a_ASN1_OBJECT() returns the number of
bytes written, even if a is invalid or contains
invalid data, but a negative value if memory allocation or a write operation
OBJ_cmp() returns 0 if the contents of
a and b are identical, or
In some cases of failure of
i2a_ASN1_OBJECT(), the reason can be determined with
Create an object for commonName:
ASN1_OBJECT *o; o = OBJ_nid2obj(NID_commonName);
Check if an object is commonName:
if (OBJ_obj2nid(obj) == NID_commonName) /* Do something */
Create a new object directly:
obj = OBJ_txt2obj("18.104.22.168", 1);
ASN1_OBJECT_new(3), BIO_new(3), d2i_ASN1_OBJECT(3), OBJ_add_sigid(3), OBJ_create(3), OBJ_NAME_add(3)
first appeared in SSLeay 0.5.1.
first appeared in SSLeay 0.6.0, and
i2t_ASN1_OBJECT() in SSLeay 0.9.0. All these
functions have been available since OpenBSD 2.4.
OBJ_txt2obj() first appeared in OpenSSL
OBJ_obj2txt() first appeared in OpenSSL
0.9.4. Both functions have been available since OpenBSD
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
NULL to determine the amount of data
that should be written. Instead buf must point to a
valid buffer and 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.