GETIPSECALGBYNAME(3NSL) Networking Services Library Functions


getipsecalgbyname, getipsecalgbynum, freeipsecalgent - query algorithm
mapping entries


cc -flag ... file ...-lnsl [ -library ... ]
#include <netdb.h>

struct ipsecalgent *getipsecalgbyname
(const char *alg_name, int protocol_num, int *errnop

struct ipsecalgent *getipsecalgbynum(int alg_num, int protocol_num,
int *errnop

void freeipsecalgent(struct ipsecalgent *ptr


Use the getipsecalgbyname(), getipsecalgbynum(), freeipsecalgent()
functions to obtain the IPsec algorithm mappings that are defined by
ipsecalgs(1M). The IPsec algorithms and associated protocol name spaces
are defined by RFC 2407.

getipsecalgbyname() and getipsecalgbynum() return a structure that
describes the algorithm entry found. This structure is described in the
RETURN VALUES section below.

freeipsecalgent() must be used by the caller to free the structures
returned by getipsecalgbyname() and getipsecalgbynum() when they are no
longer needed.

Both getipsecalgbyname() and getipsecalgbynum() take as parameter the
protocol identifier in which the algorithm is defined. See
getipsecprotobyname(3NSL) and getipsecprotobyname(3NSL).

The following protocol numbers are pre-defined:

Defines the encryption algorithms (transforms) that
can be used by IPsec to provide data confidentiality.

Defines the authentication algorithms (transforms)
that can be used by IPsec to provide authentication.

getipsecalgbyname() looks up the algorithm by its name, while
getipsecalgbynum() looks up the algorithm by its assigned number.


A pointer to an integer used to return an error status value
on certain error conditions. See ERRORS.


The getipsecalgbyname() and getipsecalgbynum() functions return a pointer
to the structure ipsecalgent_t, defined in <netdb.h>. If the requested
algorithm cannot be found, these functions return NULL.

The structure ipsecalgent_t is defined as follows:

typedef struct ipsecalgent {
char **a_names; /* algorithm names */
int a_proto_num; /* protocol number */
int a_alg_num; /* algorithm number */
char *a_mech_name; /* mechanism name */
int *a_block_sizes; /* supported block sizes */
int *a_key_sizes; /* supported key sizes */
int a_key_increment; /* key size increment */
} ipsecalgent_t;

If a_key_increment is non-zero, a_key_sizes[0] contains the default key
size for the algorithm. a_key_sizes[1] and a_key_sizes[2] specify the
smallest and biggest key sizes support by the algorithm, and
a_key_increment specifies the valid key size increments in that range.

If a_key_increment is zero, the array a_key_sizes contains the set of
key sizes, in bits, supported by the algorithm. The last key length in
the array is followed by an element of value 0. The first element of this
array is used as the default key size for the algorithm.

a_name is an array of algorithm names, terminated by an element
containing a NULL pointer. a_name[0] is the primary name for the

a_proto_num is the protocol identifer of this algorithm. a_alg_num is the
algorithm number. a_mech_name contains the mechanism name associated with
the algorithm.

a_block_sizes is an array containing the supported block lengths or MAC
lengths, in bytes, supported by the algorithm. The last valid value in
the array is followed by an element containing the value 0.


When the specified algorithm cannot be returned to the caller,
getipsecalgbynam() and getipsecalgbynum() return a value of NULL and set
the integer pointed to by the errnop parameter to one of the following

Not enough memory

Specified algorithm not found

Specified protocol number not found


See attributes(5) for descriptions of the following attributes:

|MT Level | MT Safe |
|Interface Stability | Evolving |


cryptoadm(1M), ipsecalgs(1M), getipsecprotobyname(3NSL),
getipsecprotobyname(3NSL), attributes(5)

Piper, D. RFC 2407, The Internet IP Security Domain of Interpretation for
ISAKMP. Network Working Group. November, 1998.