transform_tf.c

/* (c) 2009 Richard Andrews <andrews@ntop.org> */

#include "n2n.h"
#include "n2n_transforms.h"
#include "twofish.h"
#ifndef _MSC_VER
/* Not included in Visual Studio 2008 */
#include <strings.h> /* index() */
#endif

#define N2N_TWOFISH_NUM_SA              32 /* space for SAa */

#define N2N_TWOFISH_TRANSFORM_VERSION   1  /* version of the transform encoding */

struct sa_twofish
{
    n2n_cipherspec_t    spec;   /* cipher spec parameters */
    n2n_sa_t            sa_id;  /* security association index */
    TWOFISH            *enc_tf; /* tx state */
    TWOFISH            *dec_tf; /* rx state */
};

typedef struct sa_twofish sa_twofish_t;


/** Twofish transform state data.
 *
 *  With a key-schedule in place this will be populated with a number of
 *  SAs. Each SA has a lifetime and some opque data. The opaque data for twofish
 *  consists of the SA number and key material.
 *
 */
struct transop_tf
{
    ssize_t             tx_sa;
    size_t              num_sa;
    sa_twofish_t        sa[N2N_TWOFISH_NUM_SA];
};

typedef struct transop_tf transop_tf_t;

static int transop_deinit_twofish(n2n_trans_op_t *arg)
{
    transop_tf_t *priv = (transop_tf_t *) arg->priv;
    size_t i;

    if (priv)
    {
        /* Memory was previously allocated */
        for (i = 0; i < N2N_TWOFISH_NUM_SA; ++i)
        {
            sa_twofish_t *sa = &(priv->sa[i]);

            TwoFishDestroy(sa->enc_tf); /* deallocate TWOFISH */
            sa->enc_tf = NULL;

            TwoFishDestroy(sa->dec_tf); /* deallocate TWOFISH */
            sa->dec_tf = NULL;

            sa->sa_id = 0;
        }

        priv->num_sa = 0;
        priv->tx_sa = -1;

        free(priv);
    }

    arg->priv = NULL; /* return to fully uninitialised state */

    return 0;
}

static size_t tf_choose_tx_sa(transop_tf_t *priv)
{
    return priv->tx_sa; /* set in tick */
}

#define TRANSOP_TF_VER_SIZE     1       /* Support minor variants in encoding in one module. */
#define TRANSOP_TF_NONCE_SIZE   4
#define TRANSOP_TF_SA_SIZE      4

/** The twofish packet format consists of:
 *
 *  - a 8-bit twofish encoding version in clear text
 *  - a 32-bit SA number in clear text
 *  - ciphertext encrypted from a 32-bit nonce followed by the payload.
 *
 *  [V|SSSS|nnnnDDDDDDDDDDDDDDDDDDDDD]
 *         |<------ encrypted ------>|
 */
static int transop_encode_twofish(n2n_trans_op_t   *arg,
                                  uint8_t          *outbuf,
                                  size_t            out_len,
                                  const uint8_t    *inbuf,
                                  size_t            in_len)
{
    int len = -1;
    transop_tf_t *priv = (transop_tf_t *) arg->priv;
    uint8_t assembly[N2N_PKT_BUF_SIZE];
    uint32_t *pnonce;

    if ((in_len + TRANSOP_TF_NONCE_SIZE) <= N2N_PKT_BUF_SIZE)
    {
        if ((in_len + TRANSOP_TF_NONCE_SIZE + TRANSOP_TF_SA_SIZE + TRANSOP_TF_VER_SIZE) <= out_len)
        {
            size_t idx = 0;
            sa_twofish_t *sa;
            size_t tx_sa_num = 0;

            /* The transmit sa is periodically updated */
            tx_sa_num = tf_choose_tx_sa(priv);

            sa = &(priv->sa[tx_sa_num]); /* Proper Tx SA index */

            traceDebug("encode_twofish %lu with SA %lu.", in_len, sa->sa_id);

            /* Encode the twofish format version. */
            encode_uint8(outbuf, &idx, N2N_TWOFISH_TRANSFORM_VERSION);

            /* Encode the security association (SA) number */
            encode_uint32(outbuf, &idx, sa->sa_id);

            /* The assembly buffer is a source for encrypting data. The nonce is
             * written in first followed by the packet payload. The whole
             * contents of assembly are encrypted. */
            pnonce = (uint32_t *) assembly;
            *pnonce = rand();
            memcpy(assembly + TRANSOP_TF_NONCE_SIZE, inbuf, in_len);

            /* Encrypt the assembly contents and write the ciphertext after the SA. */
            len = TwoFishEncryptRaw(assembly, /* source */
                                    outbuf + TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE,
                                    in_len + TRANSOP_TF_NONCE_SIZE, /* enc size */
                                    sa->enc_tf);
            if (len > 0)
            {
                len += TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE; /* size of data carried in UDP. */
            }
            else
            {
                traceError("encode_twofish encryption failed.");
            }
        }
        else
        {
            traceError("encode_twofish outbuf too small.");
        }
    }
    else
    {
        traceError("encode_twofish inbuf too big to encrypt.");
    }

    return len;
}


/* Search through the array of SAs to find the one with the required ID.
 *
 * @return array index where found or -1 if not found
 */
static ssize_t twofish_find_sa(const transop_tf_t *priv, const n2n_sa_t req_id)
{
    size_t i;

    for (i = 0; i < priv->num_sa; ++i)
    {
        const sa_twofish_t *sa = NULL;

        sa = &(priv->sa[i]);
        if (req_id == sa->sa_id)
        {
            return i;
        }
    }

    return -1;
}


/** The twofish packet format consists of:
 *
 *  - a 8-bit twofish encoding version in clear text
 *  - a 32-bit SA number in clear text
 *  - ciphertext encrypted from a 32-bit nonce followed by the payload.
 *
 *  [V|SSSS|nnnnDDDDDDDDDDDDDDDDDDDDD]
 *         |<------ encrypted ------>|
 */
static int transop_decode_twofish(n2n_trans_op_t   *arg,
                                  uint8_t          *outbuf,
                                  size_t            out_len,
                                  const uint8_t    *inbuf,
                                  size_t            in_len)
{
    int len = 0;
    transop_tf_t *priv = (transop_tf_t *) arg->priv;
    uint8_t assembly[N2N_PKT_BUF_SIZE];

    if (   ((in_len - (TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE)) <= N2N_PKT_BUF_SIZE)     /* Cipher text fits in assembly */
        && (in_len >= (TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE + TRANSOP_TF_NONCE_SIZE))) /* Has at least version, SA and nonce */
    {
        n2n_sa_t sa_rx;
        ssize_t sa_idx = -1;
        size_t rem = in_len;
        size_t idx = 0;
        uint8_t tf_enc_ver = 0;

        /* Get the encoding version to make sure it is supported */
        decode_uint8(&tf_enc_ver, inbuf, &rem, &idx);

        if (N2N_TWOFISH_TRANSFORM_VERSION == tf_enc_ver)
        {
            /* Get the SA number and make sure we are decrypting with the right one. */
            decode_uint32(&sa_rx, inbuf, &rem, &idx);

            sa_idx = twofish_find_sa(priv, sa_rx);
            if (sa_idx >= 0)
            {
                sa_twofish_t *sa = &(priv->sa[sa_idx]);

                traceDebug("decode_twofish %lu with SA %lu.", in_len, sa_rx, sa->sa_id);

                len = TwoFishDecryptRaw((void *) (inbuf + TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE),
                                        assembly, /* destination */
                                        (in_len - (TRANSOP_TF_VER_SIZE + TRANSOP_TF_SA_SIZE)),
                                        sa->dec_tf);

                if (len > 0)
                {
                    /* Step over 4-byte random nonce value */
                    len -= TRANSOP_TF_NONCE_SIZE; /* size of ethernet packet */

                    memcpy(outbuf,
                           assembly + TRANSOP_TF_NONCE_SIZE,
                           len);
                }
                else
                {
                    traceError("decode_twofish decryption failed.");
                }

            }
            else
            {
                /* Wrong security association; drop the packet as it is undecodable. */
                traceError("decode_twofish SA number %lu not found.", sa_rx);

                /* REVISIT: should be able to load a new SA at this point to complete the decoding. */
            }
        }
        else
        {
            /* Wrong security association; drop the packet as it is undecodable. */
            traceError("decode_twofish unsupported twofish version %u.", tf_enc_ver);

            /* REVISIT: should be able to load a new SA at this point to complete the decoding. */
        }
    }
    else
    {
        traceError("decode_twofish inbuf wrong size (%ul) to decrypt.", in_len);
    }

    return len;
}

static int transop_addspec_twofish(n2n_trans_op_t *arg, const n2n_cipherspec_t *cspec)
{
    int retval = 1;
    ssize_t pstat = -1;
    transop_tf_t *priv = (transop_tf_t *) arg->priv;
    uint8_t keybuf[N2N_MAX_KEYSIZE];

    if (priv->num_sa < N2N_TWOFISH_NUM_SA)
    {
        const char *op = (const char *) cspec->opaque;
        const char *sep = index( op, '_' );

        if (sep)
        {
            char tmp[256];
            size_t s;

            s = sep - op;
            memcpy(tmp, cspec->opaque, s);
            tmp[s] = 0;

            s = strlen(sep + 1); /* sep is the _ which might be immediately followed by NULL */

            priv->sa[priv->num_sa].spec = *cspec;
            priv->sa[priv->num_sa].sa_id = strtoul(tmp, NULL, 10);

            pstat = n2n_parse_hex(keybuf, N2N_MAX_KEYSIZE, sep + 1, s);
            if (pstat > 0)
            {
                priv->sa[priv->num_sa].enc_tf = TwoFishInit(keybuf, pstat);
                priv->sa[priv->num_sa].dec_tf = TwoFishInit(keybuf, pstat);

                traceDebug("transop_addspec_twofish sa_id=%u data=%s.\n",
                           priv->sa[priv->num_sa].sa_id, sep + 1);

                ++(priv->num_sa);
                retval = 0;
            }
        }
        else
        {
            traceError("transop_addspec_twofish : bad key data - missing '_'.\n");
        }
    }
    else
    {
        traceError("transop_addspec_twofish : full.\n");
    }
    
    return retval;
}


static n2n_tostat_t transop_tick_twofish(n2n_trans_op_t *arg, time_t now)
{
    transop_tf_t *priv = (transop_tf_t *) arg->priv;
    size_t i;
    int found = 0;
    n2n_tostat_t r;

    memset(&r, 0, sizeof(r));

    traceDebug("transop_tf tick num_sa=%u", priv->num_sa);

    for (i = 0; i < priv->num_sa; ++i)
    {
        if (0 == validCipherSpec(&(priv->sa[i].spec), now))
        {
            time_t remaining = priv->sa[i].spec.valid_until - now;

            traceInfo("transop_tf choosing tx_sa=%u (valid for %lu sec)", priv->sa[i].sa_id, remaining);
            priv->tx_sa = i;
            found = 1;
            break;
        }
        else
        {
            traceDebug("transop_tf tick rejecting sa=%u  %lu -> %lu",
                       priv->sa[i].sa_id, priv->sa[i].spec.valid_from, priv->sa[i].spec.valid_until);
        }
    }

    if (0 == found)
    {
        traceInfo("transop_tf no keys are currently valid. Keeping tx_sa=%u", priv->tx_sa);
    }
    else
    {
        r.can_tx = 1;
        r.tx_spec.t = N2N_TRANSFORM_ID_TWOFISH;
        r.tx_spec = priv->sa[priv->tx_sa].spec;
    }

    return r;
}


int transop_twofish_setup(n2n_trans_op_t *ttt,
                          n2n_sa_t sa_num,
                          uint8_t *encrypt_pwd,
                          uint32_t encrypt_pwd_len)
{
    int retval = 1;
    transop_tf_t *priv = NULL;

    if (ttt->priv)
    {
        transop_deinit_twofish(ttt);
    }

    memset(ttt, 0, sizeof(n2n_trans_op_t));

    priv = (transop_tf_t *) malloc(sizeof(transop_tf_t));

    if (NULL != priv)
    {
        size_t i;
        sa_twofish_t *sa = NULL;

        /* install the private structure. */
        ttt->priv = priv;

        for (i = 0; i < N2N_TWOFISH_NUM_SA; ++i)
        {
            sa = &(priv->sa[i]);
            sa->sa_id = 0;
            memset(&(sa->spec), 0, sizeof(n2n_cipherspec_t));
            sa->enc_tf = NULL;
            sa->dec_tf = NULL;
        }

        priv->num_sa = 1;           /* There is one SA in the array. */
        priv->tx_sa = 0;
        sa = &(priv->sa[priv->tx_sa]);
        sa->sa_id = sa_num;
        sa->spec.valid_until = 0x7fffffff;

        /* This is a preshared key setup. Both Tx and Rx are using the same security association. */

        sa->enc_tf = TwoFishInit(encrypt_pwd, encrypt_pwd_len);
        sa->dec_tf = TwoFishInit(encrypt_pwd, encrypt_pwd_len);

        if ((sa->enc_tf) && (sa->dec_tf))
        {
            ttt->transform_id  = N2N_TRANSFORM_ID_TWOFISH;
            ttt->deinit        = transop_deinit_twofish;
            ttt->addspec       = transop_addspec_twofish;
            ttt->tick          = transop_tick_twofish; /* chooses a new tx_sa */
            ttt->fwd           = transop_encode_twofish;
            ttt->rev           = transop_decode_twofish;

            retval = 0;
        }
        else
        {
            traceError("TwoFishInit failed");
        }
    }
    else
    {
        memset(ttt, 0, sizeof(n2n_trans_op_t));
        traceError("Failed to allocate priv for twofish");
    }

    return retval;
}

int transop_twofish_init(n2n_trans_op_t *ttt)
{
    int retval = 1;
    transop_tf_t *priv = NULL;

    if (ttt->priv)
    {
        transop_deinit_twofish(ttt);
    }

    memset(ttt, 0, sizeof(n2n_trans_op_t));

    priv = (transop_tf_t *) malloc(sizeof(transop_tf_t));

    if (NULL != priv)
    {
        size_t i;
        sa_twofish_t *sa = NULL;

        /* install the private structure. */
        ttt->priv = priv;
        priv->num_sa = 0;
        priv->tx_sa  = 0; /* We will use this sa index for encoding. */

        ttt->transform_id   = N2N_TRANSFORM_ID_TWOFISH;
        ttt->addspec        = transop_addspec_twofish;
        ttt->tick           = transop_tick_twofish; /* chooses a new tx_sa */
        ttt->deinit         = transop_deinit_twofish;
        ttt->fwd            = transop_encode_twofish;
        ttt->rev            = transop_decode_twofish;

        for (i = 0; i < N2N_TWOFISH_NUM_SA; ++i)
        {
            sa = &(priv->sa[i]);
            sa->sa_id = 0;
            memset(&(sa->spec), 0, sizeof(n2n_cipherspec_t));
            sa->enc_tf = NULL;
            sa->dec_tf = NULL;
        }

        retval = 0;
    }
    else
    {
        memset(ttt, 0, sizeof(n2n_trans_op_t));
        traceError("Failed to allocate priv for twofish");
    }

    return retval;
}