ASN1对象与OID之间转换的函数,经常会用到.

Name

OBJ_nid2obj, OBJ_nid2ln, OBJ_nid2sn, OBJ_obj2nid, OBJ_txt2nid, OBJ_ln2nid, OBJ_sn2nid, OBJ_cmp, OBJ_dup, OBJ_txt2obj, OBJ_obj2txt, OBJ_create, OBJ_cleanup - ASN1 object utility functions

//OBJ_nid2obj, OBJ_nid2ln, OBJ_nid2sn, OBJ_obj2nid, OBJ_txt2nid, OBJ_ln2nid, OBJ_sn2nid, OBJ_cmp, OBJ_dup, OBJ_txt2obj, OBJ_obj2txt, OBJ_create, OBJ_cleanup这些是ASN1对象的工具函数.

Synopsis

//函数定义如下:

• ASN1_OBJECT * OBJ_nid2obj(int n);
• const char *  OBJ_nid2ln(int n);
• const char *  OBJ_nid2sn(int n);
• int OBJ_obj2nid(const ASN1_OBJECT *o);
• int OBJ_ln2nid(const char *ln);
• int OBJ_sn2nid(const char *sn);
• int OBJ_txt2nid(const char *s);
• ASN1_OBJECT * OBJ_txt2obj(const char *s, int no_name);
• int OBJ_obj2txt(char *buf, int buf_len, const ASN1_OBJECT *a, int no_name);
• int OBJ_cmp(const ASN1_OBJECT *a,const ASN1_OBJECT *b);
• ASN1_OBJECT * OBJ_dup(const ASN1_OBJECT *o);
• int OBJ_create(const char *oid,const char *sn,const char *ln);
• void OBJ_cleanup(void);

Description

//ASN1对象工具函数可将ASN1对象处理表现成一个OID的类型

The ASN1 object utility functions process ASN1_OBJECT structures which are a representation of the ASN1 OBJECT IDENTIFIER ( OID ) type.

• OBJ_nid2obj(), OBJ_nid2ln() and OBJ_nid2sn() convert the NID n to an ASN1_OBJECT structure, its long name and its short name respectively, or NULL is an error occurred. 
• OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() return the corresponding NID for the object o, the long name <ln> or the short name <sn> respectively or NID_undef if an error occurred.
• OBJ_txt2nid() returns NID corresponding to text string <s>. s can be a long name, a short name or the numerical respresentation of an object.
• OBJ_txt2obj() 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.
• OBJ_obj2txt() converts the ASN1_OBJECT a into a textual representation. The representation is written as a null 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 then if the object has a long or short name then that will be used, otherwise the numerical form will be used. If no_name is 1 then the numerical form will always be used.
• OBJ_cmp() compares a to b. If the two are identical 0 is returned.
• OBJ_dup() returns a copy of o.
• OBJ_create() adds a new object to the internal table. oid is the numerical form of the object, sn the short name and ln the long name. A new NID is returned for the created object.
• OBJ_cleanup() cleans up OpenSSLs internal object table: this should be called before an application exits if any new objects were added using OBJ_create().

Notes

Objects in OpenSSL 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 objects.h.

//Openssl的ASN1对象均是有个简称,全称以及一个数字类型的标识.一个标准的对象集合在以一个内部表形式存在,具体定义在头文件objects.h中.

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().

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 NID_undef.

Objects do not need to be in the internal tables to be processed, the functions OBJ_txt2obj() and OBJ_obj2txt() can process the numerical form of an OID .

Examples

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 NID and initialize an object from it:

int new_nid;

ASN1_OBJECT *obj;

new_nid = OBJ_create("1.2.3.4", "NewOID", "New Object Identifier");

//这样我们就可以通过OBJ_create函数,创建自己的ASN1对象了.

obj = OBJ_nid2obj(new_nid);

Create a new object directly:

obj = OBJ_txt2obj("1.2.3.4", 1);

Bugs

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.

Return Values

OBJ_nid2obj() returns an ASN1_OBJECT structure or NULL is an error occurred.

OBJ_nid2ln() and OBJ_nid2sn() returns a valid string or NULL on error.

OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() and OBJ_txt2nid() return a NID or NID_undef on error.

See Also

err_get_error(3)

History

TBA

更详细的英文说明地址:http://linux.die.net/man/3/obj_ln2nid

本文转自风车车  博客园博客，原文链接：http://www.cnblogs.com/xray2005/archive/2009/07/29/1534157.html，如需转载请自行联系原作者