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The keytab handing functions

Kerberos Keytabs

See the library functions here: Heimdal Kerberos 5 keytab handling functions

Keytabs are long term key storage for servers, their equvalment of password files.

Normally the only function that useful for server are to specify what keytab to use to other core functions like krb5_rd_req() krb5_kt_resolve(), and krb5_kt_close().

Keytab names

A keytab name is on the form type:residual. The residual part is specific to each keytab-type.

When a keytab-name is resolved, the type is matched with an internal list of keytab types. If there is no matching keytab type, the default keytab is used. The current default type is FILE.

The default value can be changed in the configuration file /etc/krb5.conf by setting the variable [defaults]default_keytab_name.

The keytab types that are implemented in Heimdal are:

Keytab example

This is a minimalistic version of ktutil.

int
main (int argc, char **argv)
{
    krb5_context context;
    krb5_keytab keytab;
    krb5_kt_cursor cursor;
    krb5_keytab_entry entry;
    krb5_error_code ret;
    char *principal;

    if (krb5_init_context (&context) != 0)
        errx(1, "krb5_context");

    ret = krb5_kt_default (context, &keytab);
    if (ret)
        krb5_err(context, 1, ret, "krb5_kt_default");

    ret = krb5_kt_start_seq_get(context, keytab, &cursor);
    if (ret)
        krb5_err(context, 1, ret, "krb5_kt_start_seq_get");
    while((ret = krb5_kt_next_entry(context, keytab, &entry, &cursor)) == 0){
        krb5_unparse_name(context, entry.principal, &principal);
        printf("principal: %s\n", principal);
        free(principal);
        krb5_kt_free_entry(context, &entry);
    }
    ret = krb5_kt_end_seq_get(context, keytab, &cursor);
    if (ret)
        krb5_err(context, 1, ret, "krb5_kt_end_seq_get");
    ret = krb5_kt_close(context, keytab);
    if (ret)
        krb5_err(context, 1, ret, "krb5_kt_close");
    krb5_free_context(context);
    return 0;
}

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