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diff --git a/crypto/heimdal/doc/programming.texi b/crypto/heimdal/doc/programming.texi new file mode 100644 index 0000000..ffcac21 --- /dev/null +++ b/crypto/heimdal/doc/programming.texi @@ -0,0 +1,287 @@ +@c $Id: programming.texi,v 1.2 2001/05/16 22:11:00 assar Exp $ + +@node Programming with Kerberos +@chapter Programming with Kerberos + +First you need to know how the Kerberos model works, go read the +introduction text (@pxref{What is Kerberos?}). + +@macro manpage{man, section} +@cite{\man\(\section\)} +@end macro + +@menu +* Kerberos 5 API Overview:: +* Walkthru a sample Kerberos 5 client:: +* Validating a password in a server application:: +@end menu + +@node Kerberos 5 API Overview, Walkthru a sample Kerberos 5 client, Programming with Kerberos, Programming with Kerberos +@section Kerberos 5 API Overview + +Most functions are documenteded in manual pages. This overview only +tries to point to where to look for a specific function. + +@subsection Kerberos context + +A kerberos context (@code{krb5_context}) holds all per thread state. All global variables that +are context specific are stored in this struture, including default +encryption types, credential-cache (ticket file), and default realms. + +See the manual pages for @manpage{krb5_context,3} and +@manpage{krb5_init_context,3}. + +@subsection Kerberos authenication context + +Kerberos authentication context (@code{krb5_auth_context}) holds all +context related to an authenticated connection, in a similar way to the +kerberos context that holds the context for the thread or process. + +The @code{krb5_auth_context} is used by various functions that are +directly related to authentication between the server/client. Example of +data that this structure contains are various flags, addresses of client +and server, port numbers, keyblocks (and subkeys), sequence numbers, +replay cache, and checksum types. + +See the manual page for @manpage{krb5_auth_context,3}. + +@subsection Keytab managment + +A keytab is a storage for locally stored keys. Heimdal includes keytab +support for Kerberos 5 keytabs, Kerberos 4 srvtab, AFS-KeyFile's, +and for storing keys in memory. + +See also manual page for @manpage{krb5_keytab,3} + +@node Walkthru a sample Kerberos 5 client, Validating a password in a server application, Kerberos 5 API Overview, Programming with Kerberos +@section Walkthru a sample Kerberos 5 client + +This example contains parts of a sample TCP Kerberos 5 clients, if you +want a real working client, please look in @file{appl/test} directory in +the Heimdal distribution. + +All Kerberos error-codes that are returned from kerberos functions in +this program are passed to @code{krb5_err}, that will print a +descriptive text of the error code and exit. Graphical programs can +convert error-code to a humal readable error-string with the +@manpage{krb5_get_err_text,3} function. + +Note that you should not use any Kerberos function before +@code{krb5_init_context()} have completed successfully. That is the +reson @code{err()} is used when @code{krb5_init_context()} fails. + +First the client needs to call @code{krb5_init_context} to initialize +the Kerberos 5 library. This is only needed once per thread +in the program. If the function returns a non-zero value it indicates +that either the Kerberos implemtation is failing or its disabled on +this host. + +@example +#include <krb5.h> + +int +main(int argc, char **argv) +@{ + krb5_context context; + + if (krb5_context(&context)) + errx (1, "krb5_context"); +@end example + +Now the client wants to connect to the host at the other end. The +preferred way of doing this is using @manpage{getaddrinfo,3} (for +operating system that have this function implemented), since getaddrinfo +is neutral to the address type and can use any protocol that is available. + +@example + struct addrinfo *ai, *a; + struct addrinfo hints; + int error; + + memset (&hints, 0, sizeof(hints)); + hints.ai_socktype = SOCK_STREAM; + hints.ai_protocol = IPPROTO_TCP; + + error = getaddrinfo (hostname, "pop3", &hints, &ai); + if (error) + errx (1, "%s: %s", hostname, gai_strerror(error)); + + for (a = ai; a != NULL; a = a->ai_next) @{ + int s; + + s = socket (a->ai_family, a->ai_socktype, a->ai_protocol); + if (s < 0) + continue; + if (connect (s, a->ai_addr, a->ai_addrlen) < 0) @{ + warn ("connect(%s)", hostname); + close (s); + continue; + @} + freeaddrinfo (ai); + ai = NULL; + @} + if (ai) @{ + freeaddrinfo (ai); + errx ("failed to contact %s", hostname); + @} +@end example + +Before authenticating, an authentication context needs to be +created. This context keeps all information for one (to be) authenticated +connection (see @manpage{krb5_auth_context,3}). + +@example + status = krb5_auth_con_init (context, &auth_context); + if (status) + krb5_err (context, 1, status, "krb5_auth_con_init"); +@end example + +For setting the address in the authentication there is a help function +@code{krb5_auth_con_setaddrs_from_fd} that does everthing that is needed +when given a connected file descriptor to the socket. + +@example + status = krb5_auth_con_setaddrs_from_fd (context, + auth_context, + &sock); + if (status) + krb5_err (context, 1, status, + "krb5_auth_con_setaddrs_from_fd"); +@end example + +The next step is to build a server principal for the service we want +to connect to. (See also @manpage{krb5_sname_to_principal,3}.) + +@example + status = krb5_sname_to_principal (context, + hostname, + service, + KRB5_NT_SRV_HST, + &server); + if (status) + krb5_err (context, 1, status, "krb5_sname_to_principal"); +@end example + +The client principal is not passed to @manpage{krb5_sendauth,3} +function, this causes the @code{krb5_sendauth} function to try to figure it +out itself. + +The server program is using the function @manpage{krb5_recvauth,3} to +receive the Kerberos 5 authenticator. + +In this case, mutual authenication will be tried. That means that the server +will authenticate to the client. Using mutual authenication +is good since it enables the user to verify that they are talking to the +right server (a server that knows the key). + +If you are using a non-blocking socket you will need to do all work of +@code{krb5_sendauth} yourself. Basically you need to send over the +authenticator from @manpage{krb5_mk_req,3} and, in case of mutual +authentication, verifying the result from the server with +@manpage{krb5_rd_rep,3}. + +@example + status = krb5_sendauth (context, + &auth_context, + &sock, + VERSION, + NULL, + server, + AP_OPTS_MUTUAL_REQUIRED, + NULL, + NULL, + NULL, + NULL, + NULL, + NULL); + if (status) + krb5_err (context, 1, status, "krb5_sendauth"); +@end example + +Once authentication has been performed, it is time to send some +data. First we create a krb5_data structure, then we sign it with +@manpage{krb5_mk_safe,3} using the @code{auth_context} that contains the +session-key that was exchanged in the +@manpage{krb5_sendauth,3}/@manpage{krb5_recvauth,3} authentication +sequence. + +@example + data.data = "hej"; + data.length = 3; + + krb5_data_zero (&packet); + + status = krb5_mk_safe (context, + auth_context, + &data, + &packet, + NULL); + if (status) + krb5_err (context, 1, status, "krb5_mk_safe"); +@end example + +And send it over the network. + +@example + len = packet.length; + net_len = htonl(len); + + if (krb5_net_write (context, &sock, &net_len, 4) != 4) + err (1, "krb5_net_write"); + if (krb5_net_write (context, &sock, packet.data, len) != len) + err (1, "krb5_net_write"); +@end example + +To send encrypted (and signed) data @manpage{krb5_mk_priv,3} should be +used instead. @manpage{krb5_mk_priv,3} works the same way as +@manpage{krb5_mk_safe,3}, with the exception that it encrypts the data +in addition to signing it. + +@example + data.data = "hemligt"; + data.length = 7; + + krb5_data_free (&packet); + + status = krb5_mk_priv (context, + auth_context, + &data, + &packet, + NULL); + if (status) + krb5_err (context, 1, status, "krb5_mk_priv"); +@end example + +And send it over the network. + +@example + len = packet.length; + net_len = htonl(len); + + if (krb5_net_write (context, &sock, &net_len, 4) != 4) + err (1, "krb5_net_write"); + if (krb5_net_write (context, &sock, packet.data, len) != len) + err (1, "krb5_net_write"); + +@end example + +The server is using @manpage{krb5_rd_safe,3} and +@manpage{krb5_rd_priv,3} to verify the signature and decrypt the packet. + +@node Validating a password in a server application, , Walkthru a sample Kerberos 5 client, Programming with Kerberos +@section Validating a password in an application + +See the manual page for @manpage{krb5_verify_user,3}. + +@c @node Why you should use GSS-API for new applications, Walkthru a sample GSS-API client, Validating a password in a server application, Programming with Kerberos +@c @section Why you should use GSS-API for new applications +@c +@c SSPI, bah, bah, microsoft, bah, bah, almost GSS-API. +@c +@c It would also be possible for other mechanisms then Kerberos, but that +@c doesn't exist any other GSS-API implementations today. +@c +@c @node Walkthru a sample GSS-API client, , Why you should use GSS-API for new applications, Programming with Kerberos +@c @section Walkthru a sample GSS-API client +@c +@c Write about how gssapi_clent.c works. |
