krb_sendauth, krb_recvauth, krb_net_write, krb_net_read - Kerberos routines for sending authentication via network stream sockets

#include <krb.h>
#include <des.h>
#include <netinet/in.h>

long options;
int fd;
KTEXT ktext;
char *service, *inst, *realm;
u_long checksum;
MSG_DAT *msg_data;
CREDENTIALS *cred;
Key_schedule schedule;
struct sockaddr_in *laddr, *faddr;
char *version;

long options;
int fd;
KTEXT ktext;
char *service, *inst;
struct sockaddr_in *faddr, *laddr;
AUTH_DAT *auth_data;
char *filename;
Key_schedule schedule;
char *version;			

int krb_net_write(fd, buf, len)
int fd;
char *buf;
int len;

int krb_net_read(fd, buf, len)
int fd;
char *buf;
int len;

These functions, which are built on top of the core Kerberos library, provide a convenient means for client and server programs to send authentication messages to one another through network connections. The krb_sendauth function sends an authenticated ticket from the client program to the server program by writing the ticket to a network socket. The krb_recvauth function receives the ticket from the client by reading from a network socket.

This function writes the ticket to the network socket specified by the file descriptor fd, returning KSUCCESS if the write proceeds successfully, and an error code if it does not.

The ktext argument should point to an allocated KTEXT_ST structure. The service, inst, and realm arguments specify the server program's Kerberos principal name, instance, and realm. If you are writing a client that uses the local realm exclusively, you can set the realm argument to NULL.

The version argument allows the client program to pass an application-specific version string that the server program can then match against its own version string. The version string can be up to KSEND_VNO_LEN (see <krb.h>) characters in length.

The checksum argument can be used to pass checksum information to the server program. The client program is responsible for specifying this information. This checksum information is difficult to corrupt because krb_sendauth passes it over the network in encrypted form. The checksum argument is passed as the checksum argument to krb_mk_req.

You can set krb_sendauth's other arguments to NULL unless you want the client and server programs to mutually authenticate themselves. In the case of mutual authentication, the client authenticates itself to the server program, and demands that the server in turn authenticate itself to the client.

If you want mutual authentication, make sure that you read all pending data from the local socket before calling krb_sendauth. Set krb_sendauth's options argument to KOPT_DO_MUTUAL (this macro is defined in the krb.h file); make sure that the laddr argument points to the address of the local socket, and that faddr points to the foreign socket's network address.

Krb_sendauth fills in the other arguments-- msg_data, cred, and schedule--before sending the ticket to the server program. You must, however, allocate space for these arguments before calling the function.

Krb_sendauth supports two other options: KOPT_DONT_MK_REQ, and KOPT_DONT_CANON. If called with options set as KOPT_DONT_MK_REQ, krb_sendauth will not use the krb_mk_req function to retrieve the ticket from the Kerberos server. The ktext argument must point to an existing ticket and authenticator (such as would be created by krb_mk_req), and the service, inst, and realm arguments can be set to NULL.

If called with options set as KOPT_DONT_CANON, krb_sendauth will not convert the service's instance to canonical form using krb_get_phost(3).

If you want to call krb_sendauth with a multiple options specification, construct options as a bitwise-OR of the options you want to specify.

The krb_recvauth function reads a ticket/authenticator pair from the socket pointed to by the fd argument. Set the options argument as a bitwise-OR of the options desired. Currently only KOPT_DO_MUTUAL is useful to the receiver.

The ktext argument should point to an allocated KTEXT_ST structure. Krb_recvauth fills ktext with the ticket/authenticator pair read from fd, then passes it to krb_rd_req.

The service and inst arguments specify the expected service and instance for which the ticket was generated. They are also passed to krb_rd_req. The inst argument may be set to "*" if the caller wishes krb_mk_req to fill in the instance used (note that there must be space in the inst argument to hold a full instance name, see krb_mk_req(3)).

The faddr argument should point to the address of the peer which is presenting the ticket. It is also passed to krb_rd_req.

If the client and server plan to mutually authenticate one another, the laddr argument should point to the local address of the file descriptor. Otherwise you can set this argument to NULL.

The auth_data argument should point to an allocated AUTH_DAT area. It is passed to and filled in by krb_rd_req. The checksum passed to the corresponding krb_sendauth is available as part of the filled-in AUTH_DAT area.

The filename argument specifies the filename which the service program should use to obtain its service key. Krb_recvauth passes filename to the krb_rd_req function. If you set this argument to "", krb_rd_req looks for the service key in the file /etc/srvtab.

If the client and server are performing mutual authenication, the schedule argument should point to an allocated Key_schedule. Otherwise it is ignored and may be NULL.

The version argument should point to a character array of at least KSEND_VNO_LEN characters. It is filled in with the version string passed by the client to krb_sendauth.

The krb_net_write function emulates the write(2) system call, but guarantees that all data specified is written to fd before returning, unless an error condition occurs.

The krb_net_read function emulates the read(2) system call, but guarantees that the requested amount of data is read from fd before returning, unless an error condition occurs.

krb_sendauth, krb_recvauth, krb_net_write, and krb_net_read will not work properly on sockets set to non-blocking I/O mode.

krb_mk_req(3), krb_rd_req(3), krb_get_phost(3)

John T. Kohl, MIT Project Athena

Copyright 1988, Massachusetts Instititute of Technology. For copying and distribution information, please see the file <mit-copyright.h>.