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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



getipsecalgbyname, getipsecalgbynum, freeipsecalgent - query algorithm mapping entries


#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(8). 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(3C) and getipsecprotobynum(3C).

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.

Return Values

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 */
     int *   a_mech_params;   /* mechanism specific parameters */
     int     a_alg_flags;     /* algorithm flags */
} ipsecalgent_t;

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

a_proto_num is the protocol identifier 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.

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.


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


Not enough memory


Specified algorithm not found


Specified protocol number not found


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

getipsecprotobyname(3C), getipsecprotobynum(3C), attributes(7), cryptoadm(8), ipsecalgs(8)

Piper, D. RFC 2407, The Internet IP Security Domain of Interpretation for ISAKMP. Network Working Group. November, 1998. https://tools.ietf.org/html/rfc2407.


These functions were added to Oracle Solaris in the Solaris 10 3/05 release.