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101 lines
4.1 KiB
101 lines
4.1 KiB
/* (c) 2009 Richard Andrews <andrews@ntop.org> */
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/** Key files
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*
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* Edge implements a very simple interface for getting instructions about
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* rolling keys.
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*
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* Key definitions are written as individual files in <transform>/<sa>.key. The
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* format of each key is a single line of hex nibbles as follows:
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*
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* 0102030405060708090a0b0c0d0e0f
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*
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* Any external key exchange mechanism can receive the key data write it into
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* the keyfiles.
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*
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* To control which keys are active at what times the key control file is
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* used. This is a single file which is periodically reread. It contains key
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* definitions in chronological order with one line per key definition as
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* follows:
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*
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* <valid_from> <valid_until> <transform> <opaque>
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*
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* edge reads the key control file periodically to get updates in policy. edge
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* holds a number of keys in memory. Data can be decoded if it was encoded by
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* any of the keys still in memory. By having at least 2 keys in memory it
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* allows for clock skew and transmission delay when encoder and decoder roll
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* keys at slightly different times. The amount of overlap in the valid time
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* ranges provides the tolerance to timing skews in the system.
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*
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* The keys have the same level of secrecy as any other user file. Existing
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* UNIX permission systems can be used to provide access controls.
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*
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*/
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/** How Edge Uses The Key Schedule
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*
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* Edge provides state space for a number of transform algorithms. Each
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* transform uses its state space to store the SA information for its keys as
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* found in the key file. When a packet is received the transform ID is in
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* plain text. The packets is then sent to that transform for decoding. Each
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* transform can store its SA numbers differently (or not at all). The
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* transform code then finds the SA number, then finds the cipher (with key) in
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* the state space and uses this to decode the packet.
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*
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* To support this, as edge reads each key line, it passes it to the
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* appropriate transform to parse the line and store the SA information in its
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* state space.
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*
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* When encoding a packet, edge has several transforms and potentially valid
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* SAs to choose from. To keep track of which one to use for encoding edge does
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* its own book-keeping as each key line is passed to the transform code: it
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* stores a lookup of valid_from -> transform. When encoding a packet it then
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* just calls the transform with the best valid_from in the table. The
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* transform's own state space has all the SAs for its keys and the best of
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* those is chosen.
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*/
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#if !defined( N2N_KEYFILE_H_ )
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#define N2N_KEYFILE_H_
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#include "n2n_wire.h"
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#include <time.h>
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#define N2N_MAX_KEYSIZE 256 /* bytes */
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#define N2N_MAX_NUM_CIPHERSPECS 8
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#define N2N_KEYPATH_SIZE 256
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#define N2N_KEYFILE_LINESIZE 256
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/** This structure stores an encryption cipher spec. */
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struct n2n_cipherspec
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{
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n2n_transform_t t; /* N2N_TRANSFORM_ID_xxx for this spec. */
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time_t valid_from; /* Start using the key at this time. */
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time_t valid_until; /* Key is valid if time < valid_until. */
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uint16_t opaque_size; /* Size in bytes of key. */
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uint8_t opaque[N2N_MAX_KEYSIZE];/* Key matter. */
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};
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typedef struct n2n_cipherspec n2n_cipherspec_t;
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static const char * const DELIMITERS=" \t\n\r";
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/** @return number of cipherspec items filled. */
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int n2n_read_keyfile( n2n_cipherspec_t * specs, /* fill out this array of cipherspecs */
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size_t numspecs, /* number of slots in the array. */
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const char * ctrlfile_path ); /* path to control file */
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int validCipherSpec( const n2n_cipherspec_t * k,
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time_t now );
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ssize_t n2n_parse_hex( uint8_t * keyBuf,
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size_t keyMax,
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const char * textKey,
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size_t textLen );
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/*----------------------------------------------------------------------------*/
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#endif /* #if !defined( N2N_KEYFILE_H_ ) */
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