ng_mppc -- Microsoft MPPC/MPPE compression and encryption netgraph node
type
#include <sys/types.h>
#include <netgraph/ng_mppc.h>
The mppc node type implements the Microsoft Point-to-Point Compression
(MPPC) and Microsoft Point-to-Point Encryption (MPPE) sub-protocols of
the PPP protocol. These protocols are often used in conjunction with the
Point-to-Point Tunneling Protocol (PPTP).
The node has two hooks, comp for compression and decomp for decompression.
Typically one or both of these hooks would be connected to the
ng_ppp(4) node type hook of the same name. Each direction of traffic
flow is independent of the other.
This node type supports the following hooks:
comp Connection to ng_ppp(4) comp hook. Incoming frames are
compressed and/or encrypted, and sent back out the same
hook.
decomp Connection to ng_ppp(4) decomp hook. Incoming frames are
decompressed and/or decrypted, and sent back out the same
hook.
This node type supports the generic control messages, plus the following:
NGM_MPPC_CONFIG_COMP
This command resets and configures the node for a session in the
outgoing traffic direction (i.e., for compression and/or encryption).
This command takes a struct ng_mppc_config as an argument:
/* Length of MPPE key */
#define MPPE_KEY_LEN 16
/* MPPC/MPPE PPP negotiation bits */
#define MPPC_BIT 0x00000001 /* mppc compression bits */
#define MPPE_40 0x00000020 /* use 40 bit key */
#define MPPE_56 0x00000080 /* use 56 bit key */
#define MPPE_128 0x00000040 /* use 128 bit key */
#define MPPE_BITS 0x000000e0 /* mppe encryption bits */
#define MPPE_STATELESS 0x01000000 /* use stateless mode */
#define MPPC_VALID_BITS 0x010000e1 /* possibly valid bits */
/* Configuration for a session */
struct ng_mppc_config {
u_char enable; /* enable */
u_int32_t bits; /* config bits */
u_char startkey[MPPE_KEY_LEN]; /* start key */
};
The enabled field enables traffic flow through the node. The bits
field contains the bits as negotiated by the Compression Control
Protocol (CCP) in PPP. The startkey is only necessary if MPPE was
negotiated, and must be equal to the session start key as defined
for MPPE. This key is based on the MS-CHAP credentials used at link
authentication time.
NGM_MPPC_CONFIG_DECOMP
This command resets and configures the node for a session in the
incoming traffic direction (i.e., for decompression and/or decryption).
This command takes a struct ng_mppc_config as an argument.
NGM_MPPC_RESETREQ
This message contains no arguments, and is bi-directional. If an
error is detected during decompression, this message is sent by the
node to the originator of the NGM_MPPC_CONFIG_DECOMP message that
initiated the session. The receiver should respond by sending a PPP
CCP Reset-Request to the peer.
This message may also be received by this node type when a CCP
Reset-Request is received by the local PPP entity. The node will
respond by flushing its outgoing compression and encryption state so
the remote side can resynchronize.
This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
when both hooks have been disconnected.
The kernel options NETGRAPH_MPPC_COMPRESSION and NETGRAPH_MPPC_ENCRYPTION
are supplied to selectively compile in either or both capabilities. At
least one of these must be defined, or else this node type is useless.
The MPPC protocol requires proprietary compression code available from
Hi/Fn (formerly STAC). These files must be obtained elsewhere and added
to the kernel sources before this node type will compile with the
NETGRAPH_MPPC_COMPRESSION option.
In PPP, encryption should be handled by the Encryption Control Protocol
(ECP) rather than CCP. However, Microsoft combined both compression and
encryption into their ``compression'' algorithm, which is confusing.
netgraph(4), ng_ppp(4), ngctl(8)
G. Pall, Microsoft Point-To-Point Compression (MPPC) Protocol, RFC 2118.
G. S. Pall and G. Zorn, Microsoft Point-To-Point Encryption (MPPE)
Protocol, draft-ietf-pppext-mppe-04.txt.
K. Hamzeh, G. Pall, W. Verthein, J. Taarud, W. Little, and G. Zorn,
Point-to-Point Tunneling Protocol (PPTP), RFC 2637.
Archie Cobbs <[email protected]>
FreeBSD 5.2.1 December 8, 1999 FreeBSD 5.2.1 [ Back ] | 