Projects/Audit

This is an early stage project for MIT Kerberos. It is being fleshed out by its proponents. Feel free to help flesh out the details of this project. After the project is ready, it will be presented for review and approval.

Purpose

Create an Audit infrastructure within MIT Kerberos to monitor security related events on the KDC. In future expand Kerberos Audit facility to the application servers, kadmin if it remains desirable.

Requirements

The new audit system should be:

• build-time enabled;
• run-time pluggable;
• simple, so it could be easily replaced with the OS specific implementations;

Events

This section details the categories of the auditable events and the associated information.

Audit module loaded/unloaded

Startup and shutdown of the audit system must be recorded by audit system;

KDC started/stopped

KDC start-up basic information: List of KDC realms and corresponding ports on which the Kerberos server should listen for UDP and TCP requests; allowable amount of clockskew in seconds; location and names of the plugins; indicator whether weak encryption types are allowed;

KDC stopped - no additional information;

Authentication

(Common Criteria Class FIA)

AS exchange:

Basic information: client principal name; requested service name; remote port; selected keytype for the ticket session key; KDC status message;

On success: tgt_id; returned ticket start, end and renew until times; ticket flags;

TGS exchange:

TGS

Basic information: tgt_id; client principal name; requested service name; remote port; authtime timestamp; selected keytype for the ticket session key; KDC status message; if the request is for referral ticket indicate to which server;

On success: returned ticket start, end and renew until times; ticket flags; if the request was to renew ticket – indicate that ticket was renewed;

Alternate

Basic information: tgt_id; client principal name; requested service name; authtime timestamp; KDC status message;

On success: alternate TGT

Cross-realm

Basic information: tgt_id; client principal name; requested service name, remote port; authtime timestamp; KDC status message;

On success: cross-realm TGT

U2U

Basic information: tgt_id; client principal name; requested service name; authtime timestamp; KDC status message;

On success: second ticket client and server name

S4U extensions

Basic information: tgt_id; client principal name; requested service name; authtime timestamp; s4u extention type; KDC status message;

On success: s4u client name

Policy: Policies violation when processing requests - TBD;

AS request

TGS request

S4U2PROXY request

Session keys 

(Common Criteria FCS_CKM.1, FCS_CKM.4):

AS and TGS exchange: tgt_id; client principal name; requested service name, remote port; authtime timestamp; keytype list in request and selected keytype for the ticket session key;

AS and TGS exchange: tgt_id; session key cleaning;

Design details

Ticket ID

We need to introduce a new concept of ticket ID tgt_id (perhaps, session key hash) that would allow to link tickets to their initial TGT.

TODO: Consider a new authorization data element AD_TKT_ID per http://tools.ietf.org/html/draft-ietf-krb-wg-cammac-03 draft.

KDC facing API

/* Audit plugin loaded/unloaded */
krb5_error_code 
load_audit_plugin(krb5_context context);
krb5_error_code 
unload_audit_plugin(krb5_context context);

/* KDC started /stopped */
krb5_error_code 
kau_kdc_start(krb5_context context, int status);
krb5_error_code 
kau_kdc_stop(krb5_context context, krb5_error_code status);

/* AS exchange: Successful (status=1) or unsuccessful (status=0) attempt */
krb5_error_code 
kau_as_req(krb5_context context, struct as_req_state *state, int status);

/* TGS exchange: Successful (status=1) or unsuccessful (status=0) attempt; alternate, u2u, s4u and cross-realm TGS */
krb5_error_code 
kau_tgs(krb5_context context,
        struct tgs_req_audit_state *state, int status);
krb5_error_code 
kau_tgs_alt(krb5_context context,
            struct tgs_req_audit_state *state, int status);
krb5_error_code
kau_tgs_u2u(krb5_context context, struct tgs_req_audit_state *state,
            krb5_principal cl2, int status);
krb5_error_code
kau_tgs_s4u(krb5_context context, struct tgs_req_audit_state *state,
            krb5_error_code status);
krb5_error_code
kau_tgs_xrealm(krb5_context context, struct tgs_req_audit_state *state,
               char* xrealm, int status);

/* Policy driven events - TBD */
krb5_error_code
kau_policy_as_req(krb5_context context, struct as_req_state *state,
                  krb5_error_code status);
krb5_error_code
kau_policy_s4u2proxy_req(krb5_context context, struct tgs_req_audit_state *state,
                         krb5_db_entry *st_client, krb5_error_code status);
krb5_error_code
kau_policy_tgs_req(krb5_context context, struct tgs_req_audit_state *state,
                   krb5_ticket *header_ticket, krb5_error_code status);

/* Session key generation and cleaning up */
krb5_error_code 
kau_sesskey_as_generated(krb5_context context,
                         struct as_req_state *state, int status);
krb5_error_code 
kau_sesskey_as_cleared(krb5_context context,
                       struct as_req_state *state, int status);
krb5_error_code 
kau_sesskey_tgs_generated(krb5_context context,
                          struct tgs_req_audit_state *state,int status);
krb5_error_code 
kau_sesskey_tgs_cleared(krb5_context context,
                        struct tgs_req_audit_state *state, int status);

/* Name of audit module */
krb5_error_code 
kau_plugin_name(krb5_context context, char **name);

struct tgs_req_audit_state {
   krb5_kdc_req *request;
   krb5_timestamp authtime;
   char *sname, *cname, *s4u_name, *u2ucname;
   krb5_principal altprinc;
   char *xrealm;
   const krb5_fulladdr *from;
   unsigned int c_flags;
   const char *status; /* KDC status message */
   krb5_enctype useenctype;
   krb5_boolean tkt_renewed;
   krb5_boolean is_referral;
};

Pluggable interface

/* Audit plugin vtable */
typedef struct krb5_audit_vtable_st {
   /* Mandatory: name of module. */
   char *name;
   kau_open_fn  open;
   kau_close_fn close;
   kau_kdc_start_fn  kdc_start;
   kau_kdc_stop_fn   kdc_stop;
   kau_as_req_fn     as_req;
   kau_tgs_fn        tgs;
   kau_tgs_alt_fn    tgs_alt;
   kau_tgs_u2u_fn    tgs_u2u;
   kau_tgs_s4u_fn    tgs_s4u;
   kau_tgs_xrealm_fn tgs_xrealm;
   kau_policy_as_req_fn        policy_as_req;
   kau_policy_tgs_req_fn       policy_tgs_req;
   kau_policy_s4u2proxy_req_fn policy_s4u2proxy_req;
   kau_sesskey_as_generated_fn  sesskey_as_generated;
   kau_sesskey_as_cleared_fn    sesskey_as_cleared;
   kau_sesskey_tgs_generated_fn sesskey_tgs_generated;
   kau_sesskey_tgs_cleared_fn   sesskey_tgs_cleared;
} *krb5_audit_vtable;

typedef krb5_error_code
(*kau_open_fn)(krb5_context context , kau_ctx *au_ctx);

typedef krb5_error_code
(*kau_close_fn)(krb5_context context, kau_ctx au_ctx);

typedef krb5_error_code
(*kau_kdc_start_fn)(krb5_context context, kau_ctx au_ctx,
                    krb5_deltat clockskew, const char *realm_port,
                    krb5_boolean allow_weak_crypto,
                    const char *plugins, const char *plugin_dir, int status);

typedef krb5_error_code
(*kau_kdc_stop_fn)(krb5_context context, kau_ctx au_ctx, krb5_error_code  status);
 
typedef krb5_error_code
(*kau_as_req_fn)(krb5_context context, kau_ctx au_ctx,                  
                 const char *cname, const char *sname,
                 const int from_port, krb5_enctype sesskey_etype,
                 krb5_flags tkt_flags, const char *tkt_cname, 
                 krb5_deltat tkt_start_time, krb5_deltat tkt_end_time, krb5_deltat tkt_renew_till,
                 const char *kdc_status, int status);

typedef krb5_error_code
(*kau_tgs_fn)(krb5_context context, kau_ctx au_ctx,
              krb5_timestamp authtime, 
              const char *cname, const char *sname,
              const int from_port,  krb5_enctype session_key_etype,
              const int is_referral, const int tkt_renewed,
              krb5_flags tkt_flags, krb5_deltat tkt_start_time,
              krb5_deltat tkt_end_time, krb5_deltat tkt_renew_till,
              const char *kdc_status, int status);

typedef krb5_error_code
(*kau_tgs_alt_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp authtime, 
                  const char *cname, const char *sname,  const char *altsrv, 
                  const int from_port, const char *kdc_status, int status);

typedef krb5_error_code
(*kau_tgs_u2u_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp authtime,
                  const char *cname, const char *sname,
                  const char *cl2, const char *srv2,
                  const int from_port, const char *kdc_status, int status);

typedef krb5_error_code
(*kau_tgs_s4u_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp authtime,
                  const char *cname, const char *sname,
                  const char * s4u_type, const char * s4u_name,
                  const int from_port, 
                  const char *kdc_status, int status);
 
typedef krb5_error_code
(*kau_tgs_xrealm_fn)(krb5_context context, kau_ctx au_ctx,
                     krb5_timestamp authtime,
                     const char *cname, const char *sname, const char *xrealm,
                     krb5_flags c_flags, krb5_flags s_flags,
                     const int from_port, const char *kdc_status, int status);

typedef krb5_error_code
(*kau_sesskey_as_generated_fn)(krb5_context context, kau_ctx au_ctx,
                               const char *cname, const char *sname,
                               const int from_port,
                               const char * ktypes, krb5_enctype used_ktype,
                               const char *kdc_status, int status);

typedef krb5_error_code
(*kau_sesskey_as_cleared_fn)(krb5_context context, kau_ctx au_ctx,
                             const char *cname, const char *sname,
                             const int from_port, krb5_enctype used_ktype,
                             const char *kdc_status, int status);

typedef krb5_error_code
(*kau_sesskey_tgs_generated_fn)(krb5_context context, kau_ctx au_ctx,
                                const char *cname, const char *sname,
                                const int from_port,
                                const char *ktypes, krb5_enctype used_ktype,
                                const char *kdc_status, int status);

typedef krb5_error_code
(*kau_sesskey_tgs_cleared_fn)(krb5_context context, kau_ctx au_ctx,                         
                              const char *cname, const char *sname,
                              const int from_port, krb5_enctype used_ktype,
                              const char *kdc_status, int status);
                                                                       

Configuration

The following ./configure option to be added:

--with-audit-plugin=simple

(For demo and testing purposes) Build the audit plugin "simple" and enable audit plugin.

Test implementation

We will use libaudit module available on Fedora, Debian, Suse for the first round.

Some "simple" audit plugin will be implemented and Python test system will become aware of its existence. New ./configure --with-audit-plugin option will be introduced to build "simple" audit plugin for testing purpose. If audit is enabled and audit plugin is available, "make check" will store audit messages into audit log file.

References

1. Common Criteria for Information Technology Security Evaluation http://www.commoncriteriaportal.org/files/ccfiles/CCPART2V3.1R4.pdf
2. Oracle Solaris Auditing http://docs.oracle.com/cd/E19963-01/html/821-1456/auditov-1.html
3. Understanding Linux Audit http://doc.opensuse.org/products/draft/SLES/SLES-security_sd_draft/cha.audit.comp.html
4. Advanced Security Audit Policy Settings http://technet.microsoft.com/en-us/library/dd772712(v=ws.10).aspx
5. Events Classification in Log Audit http://airccse.org/journal/nsa/0410ijnsa5.pdf