pgp-pubdec.c

/*
 * pgp-pubdec.c
 *      Decrypt public-key encrypted session key.
 *
 * Copyright (c) 2005 Marko Kreen
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * contrib/pgcrypto/pgp-pubdec.c
 */
#include "postgres.h"

#include "px.h"
#include "pgp.h"

/*
 * padded msg = 02 || PS || 00 || M
 * PS - pad bytes
 * M - msg
 */
static uint8 *
check_eme_pkcs1_v15(uint8 *data, int len)
{
    uint8       *data_end = data + len;
    uint8       *p = data;
    int            rnd = 0;

    if (len < 1 + 8 + 1)
        return NULL;

    if (*p++ != 2)
        return NULL;

    while (p < data_end && *p)
    {
        p++;
        rnd++;
    }

    if (p == data_end)
        return NULL;
    if (*p != 0)
        return NULL;
    if (rnd < 8)
        return NULL;
    return p + 1;
}

/*
 * secret message: 1 byte algo, sesskey, 2 byte cksum
 * ignore algo in cksum
 */
static int
control_cksum(uint8 *msg, int msglen)
{
    int            i;
    unsigned    my_cksum,
                got_cksum;

    if (msglen < 3)
        return PXE_PGP_WRONG_KEY;

    my_cksum = 0;
    for (i = 1; i < msglen - 2; i++)
        my_cksum += msg[i];
    my_cksum &= 0xFFFF;
    got_cksum = ((unsigned) (msg[msglen - 2]) << 8) + msg[msglen - 1];
    if (my_cksum != got_cksum)
    {
        px_debug("pubenc cksum failed");
        return PXE_PGP_WRONG_KEY;
    }
    return 0;
}

static int
decrypt_elgamal(PGP_PubKey *pk, PullFilter *pkt, PGP_MPI **m_p)
{
    int            res;
    PGP_MPI    *c1 = NULL;
    PGP_MPI    *c2 = NULL;

    if (pk->algo != PGP_PUB_ELG_ENCRYPT)
        return PXE_PGP_WRONG_KEY;

    /* read elgamal encrypted data */
    res = pgp_mpi_read(pkt, &c1);
    if (res < 0)
        goto out;
    res = pgp_mpi_read(pkt, &c2);
    if (res < 0)
        goto out;

    /* decrypt */
    res = pgp_elgamal_decrypt(pk, c1, c2, m_p);

out:
    pgp_mpi_free(c1);
    pgp_mpi_free(c2);
    return res;
}

static int
decrypt_rsa(PGP_PubKey *pk, PullFilter *pkt, PGP_MPI **m_p)
{
    int            res;
    PGP_MPI    *c;

    if (pk->algo != PGP_PUB_RSA_ENCRYPT
        && pk->algo != PGP_PUB_RSA_ENCRYPT_SIGN)
        return PXE_PGP_WRONG_KEY;

    /* read rsa encrypted data */
    res = pgp_mpi_read(pkt, &c);
    if (res < 0)
        return res;

    /* decrypt */
    res = pgp_rsa_decrypt(pk, c, m_p);

    pgp_mpi_free(c);
    return res;
}

/* key id is missing - user is expected to try all keys */
static const uint8
            any_key[] = {0, 0, 0, 0, 0, 0, 0, 0};

int
pgp_parse_pubenc_sesskey(PGP_Context *ctx, PullFilter *pkt)
{
    int            ver;
    int            algo;
    int            res;
    uint8        key_id[8];
    PGP_PubKey *pk;
    uint8       *msg;
    int            msglen;
    PGP_MPI    *m;

    pk = ctx->pub_key;
    if (pk == NULL)
    {
        px_debug("no pubkey?");
        return PXE_BUG;
    }

    GETBYTE(pkt, ver);
    if (ver != 3)
    {
        px_debug("unknown pubenc_sesskey pkt ver=%d", ver);
        return PXE_PGP_CORRUPT_DATA;
    }

    /*
     * check if keyid's match - user-friendly msg
     */
    res = pullf_read_fixed(pkt, 8, key_id);
    if (res < 0)
        return res;
    if (memcmp(key_id, any_key, 8) != 0
        && memcmp(key_id, pk->key_id, 8) != 0)
    {
        px_debug("key_id's does not match");
        return PXE_PGP_WRONG_KEY;
    }

    /*
     * Decrypt
     */
    GETBYTE(pkt, algo);
    switch (algo)
    {
        case PGP_PUB_ELG_ENCRYPT:
            res = decrypt_elgamal(pk, pkt, &m);
            break;
        case PGP_PUB_RSA_ENCRYPT:
        case PGP_PUB_RSA_ENCRYPT_SIGN:
            res = decrypt_rsa(pk, pkt, &m);
            break;
        default:
            res = PXE_PGP_UNKNOWN_PUBALGO;
    }
    if (res < 0)
        return res;

    /*
     * extract message
     */
    msg = check_eme_pkcs1_v15(m->data, m->bytes);
    if (msg == NULL)
    {
        px_debug("check_eme_pkcs1_v15 failed");
        res = PXE_PGP_WRONG_KEY;
        goto out;
    }
    msglen = m->bytes - (msg - m->data);

    res = control_cksum(msg, msglen);
    if (res < 0)
        goto out;

    /*
     * got sesskey
     */
    ctx->cipher_algo = *msg;
    ctx->sess_key_len = msglen - 3;
    memcpy(ctx->sess_key, msg + 1, ctx->sess_key_len);

out:
    pgp_mpi_free(m);
    if (res < 0)
        return res;
    return pgp_expect_packet_end(pkt);
}