/* Transform module - bulk data transformation */

/*
 * This file is part of secnet.
 * See README for full list of copyright holders.
 *
 * secnet is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 * 
 * secnet is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * version 3 along with secnet; if not, see
 * https://www.gnu.org/licenses/gpl.html.
 */

/* For now it's hard-coded to do sequence
   number/pkcs5/serpent-cbcmac/serpent with a 256 bit key for each
   instance of serpent. We also require key material for the IVs for
   cbcmac and cbc. Hack: we're not using full 128-bit IVs, we're just
   using 32 bits and encrypting to get the full IV to save space in
   the packets sent over the wire. */

#include <stdio.h>
#include <string.h>
#include "secnet.h"
#include "util.h"
#include "serpent.h"
#include "unaligned.h"
#include "hexdebug.h"

/* Required key length in bytes */
#define REQUIRED_KEYLEN ((512+64+32)/8)

#include "transform-common.h"

struct transform_params {
    SEQNUM_PARAMS_FIELDS;
};

struct transform {
    closure_t cl;
    struct transform_if ops;
    struct transform_params p;
};

struct transform_inst {
    struct transform_inst_if ops;
    struct transform_params p;
    struct keyInstance cryptkey;
    struct keyInstance mackey;
    uint32_t cryptiv;
    uint32_t maciv;
    SEQNUM_KEYED_FIELDS;
};

#define PKCS5_MASK 15

static bool_t transform_setkey(void *sst, uint8_t *key, int32_t keylen,
			       bool_t direction)
{
    struct transform_inst *ti=sst;

    if (keylen<REQUIRED_KEYLEN) {
	Message(M_ERR,"transform_create: insufficient key material supplied "
		"(need %d bytes, got %d)\n",REQUIRED_KEYLEN,keylen);
	return False;
    }

#if 0
    {
	printf("Setting key to: ");
	hexdebug(stdout,key,keylen);
	printf("\n");
    }
#endif /* 0 */

    serpentbe_makekey(&ti->cryptkey,256,key);
    serpentbe_makekey(&ti->mackey,256,key+32);
    ti->cryptiv=get_uint32(key+64);
    ti->maciv=get_uint32(key+68);
    uint32_t firstseq=get_uint32(key+72);
    SEQNUM_KEYED_INIT(firstseq,firstseq);

    return True;
}

TRANSFORM_VALID;

static void transform_delkey(void *sst)
{
    struct transform_inst *ti=sst;

    FILLZERO(ti->cryptkey);
    FILLZERO(ti->mackey);
    ti->keyed=False;
}

static transform_apply_return transform_forward(void *sst,
            struct buffer_if *buf, const char **errmsg)
{
    struct transform_inst *ti=sst;
    uint8_t *padp;
    int padlen;
    uint8_t iv[16];
    uint8_t macplain[16];
    uint8_t macacc[16];
    uint8_t *p, *n;
    int i;

    KEYED_CHECK;

    /* Sequence number */
    buf_prepend_uint32(buf,ti->sendseq);
    ti->sendseq++;

    /* PKCS5, stolen from IWJ */
                                    /* eg with blocksize=4 mask=3 mask+2=5   */
                                    /* msgsize    20    21    22    23   24  */
    padlen= PKCS5_MASK-buf->size;   /*           -17   -18   -19   -16  -17  */
    padlen &= PKCS5_MASK;           /*             3     2     1     0    3  */
    padlen++;                       /*             4     3     2     1    4  */

    padp=buf_append(buf,padlen);
    memset(padp,padlen,padlen);

    /* Serpent-CBCMAC. We expand the IV from 32-bit to 128-bit using
       one encryption. Then we do the MAC and append the result. We don't
       bother sending the IV - it's the same each time. (If we wanted to send
       it we've have to add 16 bytes to each message, not 4, so that the
       message stays a multiple of 16 bytes long.) */
    FILLZERO(iv);
    put_uint32(iv, ti->maciv);
    serpentbe_encrypt(&ti->mackey,iv,macacc);

    /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
       block encrypted once again. */
    for (n=buf->start; n<buf->start+buf->size; n+=16)
    {
	for (i = 0; i < 16; i++)
	    macplain[i] = macacc[i] ^ n[i];
	serpentbe_encrypt(&ti->mackey,macplain,macacc);
    }
    serpentbe_encrypt(&ti->mackey,macacc,macacc);
    BUF_ADD_BYTES(append,buf,macacc,16);

    /* Serpent-CBC. We expand the ID as for CBCMAC, do the encryption,
       and prepend the IV before increasing it. */
    FILLZERO(iv);
    put_uint32(iv, ti->cryptiv);
    serpentbe_encrypt(&ti->cryptkey,iv,iv);

    /* CBC: each block is XORed with the previous encrypted block (or the IV)
       before being encrypted. */
    p=iv;

    for (n=buf->start; n<buf->start+buf->size; n+=16)
    {
	for (i = 0; i < 16; i++)
	    n[i] ^= p[i];
	serpentbe_encrypt(&ti->cryptkey,n,n);
	p=n;
    }

    buf_prepend_uint32(buf,ti->cryptiv);
    ti->cryptiv++;
    return 0;
}

static transform_apply_return transform_reverse(void *sst,
                struct buffer_if *buf, const char **errmsg)
{
    struct transform_inst *ti=sst;
    uint8_t *padp;
    int padlen;
    int i;
    uint32_t seqnum;
    uint8_t iv[16];
    uint8_t pct[16];
    uint8_t macplain[16];
    uint8_t macacc[16];
    uint8_t *n;
    uint8_t *macexpected;

    KEYED_CHECK;

    if (buf->size < 4 + 16 + 16) {
	*errmsg="msg too short";
	return transform_apply_err;
    }

    /* CBC */
    FILLZERO(iv);
    {
	uint32_t ivword = buf_unprepend_uint32(buf);
	put_uint32(iv, ivword);
    }
    /* Assert bufsize is multiple of blocksize */
    if (buf->size&0xf) {
	*errmsg="msg not multiple of cipher blocksize";
	return transform_apply_err;
    }
    serpentbe_encrypt(&ti->cryptkey,iv,iv);
    for (n=buf->start; n<buf->start+buf->size; n+=16)
    {
	for (i = 0; i < 16; i++)
	    pct[i] = n[i];
	serpentbe_decrypt(&ti->cryptkey,n,n);
	for (i = 0; i < 16; i++)
	    n[i] ^= iv[i];
	COPY_OBJ(iv, pct);
    }

    /* CBCMAC */
    macexpected=buf_unappend(buf,16);
    FILLZERO(iv);
    put_uint32(iv, ti->maciv);
    serpentbe_encrypt(&ti->mackey,iv,macacc);

    /* CBCMAC: encrypt in CBC mode. The MAC is the last encrypted
       block encrypted once again. */
    for (n=buf->start; n<buf->start+buf->size; n+=16)
    {
	for (i = 0; i < 16; i++)
	    macplain[i] = macacc[i] ^ n[i];
	serpentbe_encrypt(&ti->mackey,macplain,macacc);
    }
    serpentbe_encrypt(&ti->mackey,macacc,macacc);
    if (!consttime_memeq(macexpected,macacc,16)) {
	*errmsg="invalid MAC";
	return transform_apply_err;
    }

    /* PKCS5, stolen from IWJ */

    padp=buf_unappend(buf,1);
    padlen=*padp;
    if (!padlen || (padlen > PKCS5_MASK+1)) {
	*errmsg="pkcs5: invalid length";
	return transform_apply_err;
    }

    buf_unappend(buf,padlen-1);

    /* Sequence number must be within max_skew of lastrecvseq; lastrecvseq
       is only allowed to increase. */
    seqnum=buf_unprepend_uint32(buf);
    SEQNUM_CHECK(seqnum, &ti->p);
    
    return 0;
}

TRANSFORM_DESTROY;

static struct transform_inst_if *transform_create(void *sst)
{
    struct transform *st=sst;

    TRANSFORM_CREATE_CORE;

    ti->p=st->p;

    return &ti->ops;
}

static list_t *transform_apply(closure_t *self, struct cloc loc,
			       dict_t *context, list_t *args)
{
    struct transform *st;
    item_t *item;
    dict_t *dict;

    NEW(st);
    st->cl.description="serpent-cbc256";
    st->cl.type=CL_TRANSFORM;
    st->cl.apply=NULL;
    st->cl.interface=&st->ops;
    st->ops.st=st;
    update_max_start_pad(&transform_max_start_pad, 28);
        /* 4byte seqnum, 16byte pad, 4byte MACIV, 4byte IV */

    /* We need 256*2 bits for serpent keys, 32 bits for CBC-IV and 32 bits
       for CBCMAC-IV, and 32 bits for init sequence number */
    st->ops.keylen=REQUIRED_KEYLEN;
    st->ops.create=transform_create;

    /* First parameter must be a dict */
    item=list_elem(args,0);
    if (!item || item->type!=t_dict)
	cfgfatal(loc,"serpent256-cbc","parameter must be a dictionary\n");
    
    dict=item->data.dict;

    SEQNUM_PARAMS_INIT(dict,&st->p,"serpent-cbc256",loc);

    SET_CAPAB_BIT(CAPAB_BIT_SERPENT256CBC);

    return new_closure(&st->cl);
}

void transform_cbcmac_module(dict_t *dict)
{
    struct keyInstance k;
    uint8_t data[32];
    uint8_t plaintext[16];
    uint8_t ciphertext[16];

    /*
     * Serpent self-test.
     * 
     * This test pattern was taken directly from the Serpent test
     * vectors, which results in a big-endian Serpent which is not
     * compatible with other implementations.
     */

    /* Serpent self-test */
    memcpy(data,
           "\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff"
           "\xff\xee\xdd\xcc\xbb\xaa\x99\x88\x77\x66\x55\x44\x33\x22\x11\x00",
           32);
    serpentbe_makekey(&k,256,data);

    memcpy(plaintext,
           "\x01\x23\x45\x67\x89\xab\xcd\xef\xfe\xdc\xba\x98\x76\x54\x32\x10",
           16);
    serpentbe_encrypt(&k,plaintext,ciphertext);

    if (memcmp(ciphertext, "\xca\x7f\xa1\x93\xe3\xeb\x9e\x99"
               "\xbd\x87\xe3\xaf\x3c\x9a\xdf\x93", 16)) {
	fatal("transform_module: serpent failed self-test (encrypt)");
    }
    serpentbe_decrypt(&k,ciphertext,plaintext);
    if (memcmp(plaintext, "\x01\x23\x45\x67\x89\xab\xcd\xef"
               "\xfe\xdc\xba\x98\x76\x54\x32\x10", 16)) {
	fatal("transform_module: serpent failed self-test (decrypt)");
    }

    add_closure(dict,"serpent256-cbc",transform_apply);

#ifdef TEST_WHOLE_TRANSFORM
    {
	struct transform *tr;
	void *ti;
	struct buffer_if buf;
	const char text[] = "This is a piece of test text.";
	char keymaterial[76] =
	    "Seventy-six bytes i"
	    "n four rows of 19; "
	    "this looks almost l"
	    "ike a poem but not.";
	const char *errmsg;
	int i;

	NEW(tr);
	tr->max_seq_skew = 20;
	ti = transform_create(tr);

	transform_setkey(ti, keymaterial, 76);

        buf.base = malloc(4096);
	buffer_init(&buf, 2048);
	BUF_ADD_OBJ(append, buf, text, sizeof(text));
	if (transform_forward(ti, &buf, &errmsg)) {
	    fatal("transform_forward test: %s", errmsg);
	}
	printf("transformed text is:\n");
	for (i = 0; i < buf.size; i++)
	    printf("%02x%c", buf.start[i],
		   (i%16==15 || i==buf.size-1 ? '\n' : ' '));
	if (transform_reverse(ti, &buf, &errmsg)) {
	    fatal("transform_reverse test: %s", errmsg);
	}
	printf("transform reversal worked OK\n");
    }
#endif
}