pgp-decrypt.c

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/*
 * pgp-decrypt.c
 *    OpenPGP decrypt.
 *
 * 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-decrypt.c
 */

#include "postgres.h"

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

#define NO_CTX_SIZE     0
#define ALLOW_CTX_SIZE  1
#define NO_COMPR        0
#define ALLOW_COMPR     1
#define NO_MDC          0
#define NEED_MDC        1

#define PKT_NORMAL 1
#define PKT_STREAM 2
#define PKT_CONTEXT 3

#define MAX_CHUNK (16*1024*1024)

static int
parse_new_len(PullFilter *src, int *len_p)
{
    uint8       b;
    int         len;
    int         pkttype = PKT_NORMAL;

    GETBYTE(src, b);
    if (b <= 191)
        len = b;
    else if (b >= 192 && b <= 223)
    {
        len = ((unsigned) (b) - 192) << 8;
        GETBYTE(src, b);
        len += 192 + b;
    }
    else if (b == 255)
    {
        GETBYTE(src, b);
        len = b;
        GETBYTE(src, b);
        len = (len << 8) | b;
        GETBYTE(src, b);
        len = (len << 8) | b;
        GETBYTE(src, b);
        len = (len << 8) | b;
    }
    else
    {
        len = 1 << (b & 0x1F);
        pkttype = PKT_STREAM;
    }

    if (len < 0 || len > MAX_CHUNK)
    {
        px_debug("parse_new_len: weird length");
        return PXE_PGP_CORRUPT_DATA;
    }

    *len_p = len;
    return pkttype;
}

static int
parse_old_len(PullFilter *src, int *len_p, int lentype)
{
    uint8       b;
    int         len;

    GETBYTE(src, b);
    len = b;

    if (lentype == 1)
    {
        GETBYTE(src, b);
        len = (len << 8) | b;
    }
    else if (lentype == 2)
    {
        GETBYTE(src, b);
        len = (len << 8) | b;
        GETBYTE(src, b);
        len = (len << 8) | b;
        GETBYTE(src, b);
        len = (len << 8) | b;
    }

    if (len < 0 || len > MAX_CHUNK)
    {
        px_debug("parse_old_len: weird length");
        return PXE_PGP_CORRUPT_DATA;
    }
    *len_p = len;
    return PKT_NORMAL;
}

/* returns pkttype or 0 on eof */
int
pgp_parse_pkt_hdr(PullFilter *src, uint8 *tag, int *len_p, int allow_ctx)
{
    int         lentype;
    int         res;
    uint8      *p;

    /* EOF is normal here, thus we don't use GETBYTE */
    res = pullf_read(src, 1, &p);
    if (res < 0)
        return res;
    if (res == 0)
        return 0;

    if ((*p & 0x80) == 0)
    {
        px_debug("pgp_parse_pkt_hdr: not pkt hdr");
        return PXE_PGP_CORRUPT_DATA;
    }

    if (*p & 0x40)
    {
        *tag = *p & 0x3f;
        res = parse_new_len(src, len_p);
    }
    else
    {
        lentype = *p & 3;
        *tag = (*p >> 2) & 0x0F;
        if (lentype == 3)
            res = allow_ctx ? PKT_CONTEXT : PXE_PGP_CORRUPT_DATA;
        else
            res = parse_old_len(src, len_p, lentype);
    }
    return res;
}

/*
 * Packet reader
 */
struct PktData
{
    int         type;
    int         len;
};

static int
pktreader_pull(void *priv, PullFilter *src, int len,
               uint8 **data_p, uint8 *buf, int buflen)
{
    int         res;
    struct PktData *pkt = priv;

    /* PKT_CONTEXT means: whatever there is */
    if (pkt->type == PKT_CONTEXT)
        return pullf_read(src, len, data_p);

    while (pkt->len == 0)
    {
        /* this was last chunk in stream */
        if (pkt->type == PKT_NORMAL)
            return 0;

        /* next chunk in stream */
        res = parse_new_len(src, &pkt->len);
        if (res < 0)
            return res;
        pkt->type = res;
    }

    if (len > pkt->len)
        len = pkt->len;

    res = pullf_read(src, len, data_p);
    if (res > 0)
        pkt->len -= res;

    return res;
}

static void
pktreader_free(void *priv)
{
    struct PktData *pkt = priv;

    px_memset(pkt, 0, sizeof(*pkt));
    px_free(pkt);
}

static struct PullFilterOps pktreader_filter = {
    NULL, pktreader_pull, pktreader_free
};

/* needs helper function to pass several parameters */
int
pgp_create_pkt_reader(PullFilter **pf_p, PullFilter *src, int len,
                      int pkttype, PGP_Context *ctx)
{
    int         res;
    struct PktData *pkt = px_alloc(sizeof(*pkt));

    pkt->type = pkttype;
    pkt->len = len;
    res = pullf_create(pf_p, &pktreader_filter, pkt, src);
    if (res < 0)
        px_free(pkt);
    return res;
}

/*
 * Prefix check filter
 * https://tools.ietf.org/html/rfc4880#section-5.7
 * https://tools.ietf.org/html/rfc4880#section-5.13
 */

static int
prefix_init(void **priv_p, void *arg, PullFilter *src)
{
    PGP_Context *ctx = arg;
    int         len;
    int         res;
    uint8      *buf;
    uint8       tmpbuf[PGP_MAX_BLOCK + 2];

    len = pgp_get_cipher_block_size(ctx->cipher_algo);
    if (len > sizeof(tmpbuf))
        return PXE_BUG;

    res = pullf_read_max(src, len + 2, &buf, tmpbuf);
    if (res < 0)
        return res;
    if (res != len + 2)
    {
        px_debug("prefix_init: short read");
        px_memset(tmpbuf, 0, sizeof(tmpbuf));
        return PXE_PGP_CORRUPT_DATA;
    }

    if (buf[len - 2] != buf[len] || buf[len - 1] != buf[len + 1])
    {
        px_debug("prefix_init: corrupt prefix");
        /* report error in pgp_decrypt() */
        ctx->corrupt_prefix = 1;
    }
    px_memset(tmpbuf, 0, sizeof(tmpbuf));
    return 0;
}

static struct PullFilterOps prefix_filter = {
    prefix_init, NULL, NULL
};


/*
 * Decrypt filter
 */

static int
decrypt_init(void **priv_p, void *arg, PullFilter *src)
{
    PGP_CFB    *cfb = arg;

    *priv_p = cfb;

    /* we need to write somewhere, so ask for a buffer */
    return 4096;
}

static int
decrypt_read(void *priv, PullFilter *src, int len,
             uint8 **data_p, uint8 *buf, int buflen)
{
    PGP_CFB    *cfb = priv;
    uint8      *tmp;
    int         res;

    res = pullf_read(src, len, &tmp);
    if (res > 0)
    {
        pgp_cfb_decrypt(cfb, tmp, res, buf);
        *data_p = buf;
    }
    return res;
}

struct PullFilterOps pgp_decrypt_filter = {
    decrypt_init, decrypt_read, NULL
};


/*
 * MDC hasher filter
 */

static int
mdc_init(void **priv_p, void *arg, PullFilter *src)
{
    PGP_Context *ctx = arg;

    *priv_p = ctx;
    return pgp_load_digest(PGP_DIGEST_SHA1, &ctx->mdc_ctx);
}

static void
mdc_free(void *priv)
{
    PGP_Context *ctx = priv;

    if (ctx->use_mdcbuf_filter)
        return;
    px_md_free(ctx->mdc_ctx);
    ctx->mdc_ctx = NULL;
}

static int
mdc_finish(PGP_Context *ctx, PullFilter *src, int len)
{
    int         res;
    uint8       hash[20];
    uint8       tmpbuf[20];
    uint8      *data;

    /* should not happen */
    if (ctx->use_mdcbuf_filter)
        return PXE_BUG;

    /* It's SHA1 */
    if (len != 20)
        return PXE_PGP_CORRUPT_DATA;

    /* mdc_read should not call px_md_update */
    ctx->in_mdc_pkt = 1;

    /* read data */
    res = pullf_read_max(src, len, &data, tmpbuf);
    if (res < 0)
        return res;
    if (res == 0)
    {
        px_debug("no mdc");
        return PXE_PGP_CORRUPT_DATA;
    }

    /* is the packet sane? */
    if (res != 20)
    {
        px_debug("mdc_finish: read failed, res=%d", res);
        return PXE_PGP_CORRUPT_DATA;
    }

    /*
     * ok, we got the hash, now check
     */
    px_md_finish(ctx->mdc_ctx, hash);
    res = memcmp(hash, data, 20);
    px_memset(hash, 0, 20);
    px_memset(tmpbuf, 0, sizeof(tmpbuf));
    if (res != 0)
    {
        px_debug("mdc_finish: mdc failed");
        return PXE_PGP_CORRUPT_DATA;
    }
    ctx->mdc_checked = 1;
    return 0;
}

static int
mdc_read(void *priv, PullFilter *src, int len,
         uint8 **data_p, uint8 *buf, int buflen)
{
    int         res;
    PGP_Context *ctx = priv;

    /* skip this filter? */
    if (ctx->use_mdcbuf_filter || ctx->in_mdc_pkt)
        return pullf_read(src, len, data_p);

    res = pullf_read(src, len, data_p);
    if (res < 0)
        return res;
    if (res == 0)
    {
        px_debug("mdc_read: unexpected eof");
        return PXE_PGP_CORRUPT_DATA;
    }
    px_md_update(ctx->mdc_ctx, *data_p, res);

    return res;
}

static struct PullFilterOps mdc_filter = {
    mdc_init, mdc_read, mdc_free
};


/*
 * Combined Pkt reader and MDC hasher.
 *
 * For the case of SYMENCRYPTED_DATA_MDC packet, where
 * the data part has 'context length', which means
 * that data packet ends 22 bytes before end of parent
 * packet, which is silly.
 */
#define MDCBUF_LEN 8192
struct MDCBufData
{
    PGP_Context *ctx;
    int         eof;
    int         buflen;
    int         avail;
    uint8      *pos;
    int         mdc_avail;
    uint8       mdc_buf[22];
    uint8       buf[MDCBUF_LEN];
};

static int
mdcbuf_init(void **priv_p, void *arg, PullFilter *src)
{
    PGP_Context *ctx = arg;
    struct MDCBufData *st;

    st = px_alloc(sizeof(*st));
    memset(st, 0, sizeof(*st));
    st->buflen = sizeof(st->buf);
    st->ctx = ctx;
    *priv_p = st;

    /* take over the work of mdc_filter */
    ctx->use_mdcbuf_filter = 1;

    return 0;
}

static int
mdcbuf_finish(struct MDCBufData *st)
{
    uint8       hash[20];
    int         res;

    st->eof = 1;

    if (st->mdc_buf[0] != 0xD3 || st->mdc_buf[1] != 0x14)
    {
        px_debug("mdcbuf_finish: bad MDC pkt hdr");
        return PXE_PGP_CORRUPT_DATA;
    }
    px_md_update(st->ctx->mdc_ctx, st->mdc_buf, 2);
    px_md_finish(st->ctx->mdc_ctx, hash);
    res = memcmp(hash, st->mdc_buf + 2, 20);
    px_memset(hash, 0, 20);
    if (res)
    {
        px_debug("mdcbuf_finish: MDC does not match");
        res = PXE_PGP_CORRUPT_DATA;
    }
    return res;
}

static void
mdcbuf_load_data(struct MDCBufData *st, uint8 *src, int len)
{
    uint8      *dst = st->pos + st->avail;

    memcpy(dst, src, len);
    px_md_update(st->ctx->mdc_ctx, src, len);
    st->avail += len;
}

static void
mdcbuf_load_mdc(struct MDCBufData *st, uint8 *src, int len)
{
    memmove(st->mdc_buf + st->mdc_avail, src, len);
    st->mdc_avail += len;
}

static int
mdcbuf_refill(struct MDCBufData *st, PullFilter *src)
{
    uint8      *data;
    int         res;
    int         need;

    /* put avail data in start */
    if (st->avail > 0 && st->pos != st->buf)
        memmove(st->buf, st->pos, st->avail);
    st->pos = st->buf;

    /* read new data */
    need = st->buflen + 22 - st->avail - st->mdc_avail;
    res = pullf_read(src, need, &data);
    if (res < 0)
        return res;
    if (res == 0)
        return mdcbuf_finish(st);

    /* add to buffer */
    if (res >= 22)
    {
        mdcbuf_load_data(st, st->mdc_buf, st->mdc_avail);
        st->mdc_avail = 0;

        mdcbuf_load_data(st, data, res - 22);
        mdcbuf_load_mdc(st, data + res - 22, 22);
    }
    else
    {
        int         canmove = st->mdc_avail + res - 22;

        if (canmove > 0)
        {
            mdcbuf_load_data(st, st->mdc_buf, canmove);
            st->mdc_avail -= canmove;
            memmove(st->mdc_buf, st->mdc_buf + canmove, st->mdc_avail);
        }
        mdcbuf_load_mdc(st, data, res);
    }
    return 0;
}

static int
mdcbuf_read(void *priv, PullFilter *src, int len,
            uint8 **data_p, uint8 *buf, int buflen)
{
    struct MDCBufData *st = priv;
    int         res;

    if (!st->eof && len > st->avail)
    {
        res = mdcbuf_refill(st, src);
        if (res < 0)
            return res;
    }

    if (len > st->avail)
        len = st->avail;

    *data_p = st->pos;
    st->pos += len;
    st->avail -= len;
    return len;
}

static void
mdcbuf_free(void *priv)
{
    struct MDCBufData *st = priv;

    px_md_free(st->ctx->mdc_ctx);
    st->ctx->mdc_ctx = NULL;
    px_memset(st, 0, sizeof(*st));
    px_free(st);
}

static struct PullFilterOps mdcbuf_filter = {
    mdcbuf_init, mdcbuf_read, mdcbuf_free
};


/*
 * Decrypt separate session key
 */
static int
decrypt_key(PGP_Context *ctx, const uint8 *src, int len)
{
    int         res;
    uint8       algo;
    PGP_CFB    *cfb;

    res = pgp_cfb_create(&cfb, ctx->s2k_cipher_algo,
                         ctx->s2k.key, ctx->s2k.key_len, 0, NULL);
    if (res < 0)
        return res;

    pgp_cfb_decrypt(cfb, src, 1, &algo);
    src++;
    len--;

    pgp_cfb_decrypt(cfb, src, len, ctx->sess_key);
    pgp_cfb_free(cfb);
    ctx->sess_key_len = len;
    ctx->cipher_algo = algo;

    if (pgp_get_cipher_key_size(algo) != len)
    {
        px_debug("sesskey bad len: algo=%d, expected=%d, got=%d",
                 algo, pgp_get_cipher_key_size(algo), len);
        return PXE_PGP_CORRUPT_DATA;
    }
    return 0;
}

/*
 * Handle key packet
 */
static int
parse_symenc_sesskey(PGP_Context *ctx, PullFilter *src)
{
    uint8      *p;
    int         res;
    uint8       tmpbuf[PGP_MAX_KEY + 2];
    uint8       ver;

    GETBYTE(src, ver);
    GETBYTE(src, ctx->s2k_cipher_algo);
    if (ver != 4)
    {
        px_debug("bad key pkt ver");
        return PXE_PGP_CORRUPT_DATA;
    }

    /*
     * read S2K info
     */
    res = pgp_s2k_read(src, &ctx->s2k);
    if (res < 0)
        return res;
    ctx->s2k_mode = ctx->s2k.mode;
    ctx->s2k_count = s2k_decode_count(ctx->s2k.iter);
    ctx->s2k_digest_algo = ctx->s2k.digest_algo;

    /*
     * generate key from password
     */
    res = pgp_s2k_process(&ctx->s2k, ctx->s2k_cipher_algo,
                          ctx->sym_key, ctx->sym_key_len);
    if (res < 0)
        return res;

    /*
     * do we have separate session key?
     */
    res = pullf_read_max(src, PGP_MAX_KEY + 2, &p, tmpbuf);
    if (res < 0)
        return res;

    if (res == 0)
    {
        /*
         * no, s2k key is session key
         */
        memcpy(ctx->sess_key, ctx->s2k.key, ctx->s2k.key_len);
        ctx->sess_key_len = ctx->s2k.key_len;
        ctx->cipher_algo = ctx->s2k_cipher_algo;
        res = 0;
        ctx->use_sess_key = 0;
    }
    else
    {
        /*
         * yes, decrypt it
         */
        if (res < 17 || res > PGP_MAX_KEY + 1)
        {
            px_debug("expect key, but bad data");
            return PXE_PGP_CORRUPT_DATA;
        }
        ctx->use_sess_key = 1;
        res = decrypt_key(ctx, p, res);
    }

    px_memset(tmpbuf, 0, sizeof(tmpbuf));
    return res;
}

static int
copy_crlf(MBuf *dst, uint8 *data, int len, int *got_cr)
{
    uint8      *data_end = data + len;
    uint8       tmpbuf[1024];
    uint8      *tmp_end = tmpbuf + sizeof(tmpbuf);
    uint8      *p;
    int         res;

    p = tmpbuf;
    if (*got_cr)
    {
        if (*data != '\n')
            *p++ = '\r';
        *got_cr = 0;
    }
    while (data < data_end)
    {
        if (*data == '\r')
        {
            if (data + 1 < data_end)
            {
                if (*(data + 1) == '\n')
                    data++;
            }
            else
            {
                *got_cr = 1;
                break;
            }
        }
        *p++ = *data++;
        if (p >= tmp_end)
        {
            res = mbuf_append(dst, tmpbuf, p - tmpbuf);
            if (res < 0)
                return res;
            p = tmpbuf;
        }
    }
    if (p - tmpbuf > 0)
    {
        res = mbuf_append(dst, tmpbuf, p - tmpbuf);
        if (res < 0)
            return res;
    }
    px_memset(tmpbuf, 0, sizeof(tmpbuf));
    return 0;
}

static int
parse_literal_data(PGP_Context *ctx, MBuf *dst, PullFilter *pkt)
{
    int         type;
    int         name_len;
    int         res;
    uint8      *buf;
    uint8       tmpbuf[4];
    int         got_cr = 0;

    GETBYTE(pkt, type);
    GETBYTE(pkt, name_len);

    /* skip name */
    while (name_len > 0)
    {
        res = pullf_read(pkt, name_len, &buf);
        if (res < 0)
            return res;
        if (res == 0)
            break;
        name_len -= res;
    }
    if (name_len > 0)
    {
        px_debug("parse_literal_data: unexpected eof");
        return PXE_PGP_CORRUPT_DATA;
    }

    /* skip date */
    res = pullf_read_max(pkt, 4, &buf, tmpbuf);
    if (res != 4)
    {
        px_debug("parse_literal_data: unexpected eof");
        return PXE_PGP_CORRUPT_DATA;
    }
    px_memset(tmpbuf, 0, 4);

    /*
     * If called from an SQL function that returns text, pgp_decrypt() rejects
     * inputs not self-identifying as text.
     */
    if (ctx->text_mode)
        if (type != 't' && type != 'u')
        {
            px_debug("parse_literal_data: data type=%c", type);
            ctx->unexpected_binary = true;
        }

    ctx->unicode_mode = (type == 'u') ? 1 : 0;

    /* read data */
    while (1)
    {
        res = pullf_read(pkt, 32 * 1024, &buf);
        if (res <= 0)
            break;

        if (ctx->text_mode && ctx->convert_crlf)
            res = copy_crlf(dst, buf, res, &got_cr);
        else
            res = mbuf_append(dst, buf, res);
        if (res < 0)
            break;
    }
    if (res >= 0 && got_cr)
        res = mbuf_append(dst, (const uint8 *) "\r", 1);
    return res;
}

/* process_data_packets and parse_compressed_data call each other */
static int  process_data_packets(PGP_Context *ctx, MBuf *dst,
                                 PullFilter *src, int allow_compr, int need_mdc);

static int
parse_compressed_data(PGP_Context *ctx, MBuf *dst, PullFilter *pkt)
{
    int         res;
    uint8       type;
    PullFilter *pf_decompr;
    uint8      *discard_buf;

    GETBYTE(pkt, type);

    ctx->compress_algo = type;
    switch (type)
    {
        case PGP_COMPR_NONE:
            res = process_data_packets(ctx, dst, pkt, NO_COMPR, NO_MDC);
            break;

        case PGP_COMPR_ZIP:
        case PGP_COMPR_ZLIB:
            res = pgp_decompress_filter(&pf_decompr, ctx, pkt);
            if (res >= 0)
            {
                res = process_data_packets(ctx, dst, pf_decompr,
                                           NO_COMPR, NO_MDC);
                pullf_free(pf_decompr);
            }
            break;

        case PGP_COMPR_BZIP2:
            px_debug("parse_compressed_data: bzip2 unsupported");
            /* report error in pgp_decrypt() */
            ctx->unsupported_compr = 1;

            /*
             * Discard the compressed data, allowing it to first affect any
             * MDC digest computation.
             */
            while (1)
            {
                res = pullf_read(pkt, 32 * 1024, &discard_buf);
                if (res <= 0)
                    break;
            }

            break;

        default:
            px_debug("parse_compressed_data: unknown compr type");
            res = PXE_PGP_CORRUPT_DATA;
    }

    return res;
}

static int
process_data_packets(PGP_Context *ctx, MBuf *dst, PullFilter *src,
                     int allow_compr, int need_mdc)
{
    uint8       tag;
    int         len,
                res;
    int         got_data = 0;
    int         got_mdc = 0;
    PullFilter *pkt = NULL;

    while (1)
    {
        res = pgp_parse_pkt_hdr(src, &tag, &len, ALLOW_CTX_SIZE);
        if (res <= 0)
            break;


        /* mdc packet should be last */
        if (got_mdc)
        {
            px_debug("process_data_packets: data after mdc");
            res = PXE_PGP_CORRUPT_DATA;
            break;
        }

        /*
         * Context length inside SYMENCRYPTED_DATA_MDC packet needs special
         * handling.
         */
        if (need_mdc && res == PKT_CONTEXT)
            res = pullf_create(&pkt, &mdcbuf_filter, ctx, src);
        else
            res = pgp_create_pkt_reader(&pkt, src, len, res, ctx);
        if (res < 0)
            break;

        switch (tag)
        {
            case PGP_PKT_LITERAL_DATA:
                got_data = 1;
                res = parse_literal_data(ctx, dst, pkt);
                break;
            case PGP_PKT_COMPRESSED_DATA:
                if (allow_compr == 0)
                {
                    px_debug("process_data_packets: unexpected compression");
                    res = PXE_PGP_CORRUPT_DATA;
                }
                else if (got_data)
                {
                    /*
                     * compr data must be alone
                     */
                    px_debug("process_data_packets: only one cmpr pkt allowed");
                    res = PXE_PGP_CORRUPT_DATA;
                }
                else
                {
                    got_data = 1;
                    res = parse_compressed_data(ctx, dst, pkt);
                }
                break;
            case PGP_PKT_MDC:
                if (need_mdc == NO_MDC)
                {
                    px_debug("process_data_packets: unexpected MDC");
                    res = PXE_PGP_CORRUPT_DATA;
                    break;
                }

                res = mdc_finish(ctx, pkt, len);
                if (res >= 0)
                    got_mdc = 1;
                break;
            default:
                px_debug("process_data_packets: unexpected pkt tag=%d", tag);
                res = PXE_PGP_CORRUPT_DATA;
        }

        pullf_free(pkt);
        pkt = NULL;

        if (res < 0)
            break;
    }

    if (pkt)
        pullf_free(pkt);

    if (res < 0)
        return res;

    if (!got_data)
    {
        px_debug("process_data_packets: no data");
        res = PXE_PGP_CORRUPT_DATA;
    }
    if (need_mdc && !got_mdc && !ctx->use_mdcbuf_filter)
    {
        px_debug("process_data_packets: got no mdc");
        res = PXE_PGP_CORRUPT_DATA;
    }
    return res;
}

static int
parse_symenc_data(PGP_Context *ctx, PullFilter *pkt, MBuf *dst)
{
    int         res;
    PGP_CFB    *cfb = NULL;
    PullFilter *pf_decrypt = NULL;
    PullFilter *pf_prefix = NULL;

    res = pgp_cfb_create(&cfb, ctx->cipher_algo,
                         ctx->sess_key, ctx->sess_key_len, 1, NULL);
    if (res < 0)
        goto out;

    res = pullf_create(&pf_decrypt, &pgp_decrypt_filter, cfb, pkt);
    if (res < 0)
        goto out;

    res = pullf_create(&pf_prefix, &prefix_filter, ctx, pf_decrypt);
    if (res < 0)
        goto out;

    res = process_data_packets(ctx, dst, pf_prefix, ALLOW_COMPR, NO_MDC);

out:
    if (pf_prefix)
        pullf_free(pf_prefix);
    if (pf_decrypt)
        pullf_free(pf_decrypt);
    if (cfb)
        pgp_cfb_free(cfb);

    return res;
}

static int
parse_symenc_mdc_data(PGP_Context *ctx, PullFilter *pkt, MBuf *dst)
{
    int         res;
    PGP_CFB    *cfb = NULL;
    PullFilter *pf_decrypt = NULL;
    PullFilter *pf_prefix = NULL;
    PullFilter *pf_mdc = NULL;
    uint8       ver;

    GETBYTE(pkt, ver);
    if (ver != 1)
    {
        px_debug("parse_symenc_mdc_data: pkt ver != 1");
        return PXE_PGP_CORRUPT_DATA;
    }

    res = pgp_cfb_create(&cfb, ctx->cipher_algo,
                         ctx->sess_key, ctx->sess_key_len, 0, NULL);
    if (res < 0)
        goto out;

    res = pullf_create(&pf_decrypt, &pgp_decrypt_filter, cfb, pkt);
    if (res < 0)
        goto out;

    res = pullf_create(&pf_mdc, &mdc_filter, ctx, pf_decrypt);
    if (res < 0)
        goto out;

    res = pullf_create(&pf_prefix, &prefix_filter, ctx, pf_mdc);
    if (res < 0)
        goto out;

    res = process_data_packets(ctx, dst, pf_prefix, ALLOW_COMPR, NEED_MDC);

out:
    if (pf_prefix)
        pullf_free(pf_prefix);
    if (pf_mdc)
        pullf_free(pf_mdc);
    if (pf_decrypt)
        pullf_free(pf_decrypt);
    if (cfb)
        pgp_cfb_free(cfb);

    return res;
}

/*
 * skip over packet contents
 */
int
pgp_skip_packet(PullFilter *pkt)
{
    int         res = 1;
    uint8      *tmp;

    while (res > 0)
        res = pullf_read(pkt, 32 * 1024, &tmp);
    return res;
}

/*
 * expect to be at packet end, any data is error
 */
int
pgp_expect_packet_end(PullFilter *pkt)
{
    int         res;
    uint8      *tmp;

    res = pullf_read(pkt, 32 * 1024, &tmp);
    if (res > 0)
    {
        px_debug("pgp_expect_packet_end: got data");
        return PXE_PGP_CORRUPT_DATA;
    }
    return res;
}

int
pgp_decrypt(PGP_Context *ctx, MBuf *msrc, MBuf *mdst)
{
    int         res;
    PullFilter *src = NULL;
    PullFilter *pkt = NULL;
    uint8       tag;
    int         len;
    int         got_key = 0;
    int         got_data = 0;

    res = pullf_create_mbuf_reader(&src, msrc);

    while (res >= 0)
    {
        res = pgp_parse_pkt_hdr(src, &tag, &len, NO_CTX_SIZE);
        if (res <= 0)
            break;

        res = pgp_create_pkt_reader(&pkt, src, len, res, ctx);
        if (res < 0)
            break;

        res = PXE_PGP_CORRUPT_DATA;
        switch (tag)
        {
            case PGP_PKT_MARKER:
                res = pgp_skip_packet(pkt);
                break;
            case PGP_PKT_PUBENCRYPTED_SESSKEY:
                /* fixme: skip those */
                res = pgp_parse_pubenc_sesskey(ctx, pkt);
                got_key = 1;
                break;
            case PGP_PKT_SYMENCRYPTED_SESSKEY:
                if (got_key)

                    /*
                     * Theoretically, there could be several keys, both public
                     * and symmetric, all of which encrypt same session key.
                     * Decrypt should try with each one, before failing.
                     */
                    px_debug("pgp_decrypt: using first of several keys");
                else
                {
                    got_key = 1;
                    res = parse_symenc_sesskey(ctx, pkt);
                }
                break;
            case PGP_PKT_SYMENCRYPTED_DATA:
                if (!got_key)
                    px_debug("pgp_decrypt: have data but no key");
                else if (got_data)
                    px_debug("pgp_decrypt: got second data packet");
                else
                {
                    got_data = 1;
                    ctx->disable_mdc = 1;
                    res = parse_symenc_data(ctx, pkt, mdst);
                }
                break;
            case PGP_PKT_SYMENCRYPTED_DATA_MDC:
                if (!got_key)
                    px_debug("pgp_decrypt: have data but no key");
                else if (got_data)
                    px_debug("pgp_decrypt: several data pkts not supported");
                else
                {
                    got_data = 1;
                    ctx->disable_mdc = 0;
                    res = parse_symenc_mdc_data(ctx, pkt, mdst);
                }
                break;
            default:
                px_debug("pgp_decrypt: unknown tag: 0x%02x", tag);
        }
        pullf_free(pkt);
        pkt = NULL;
    }

    if (pkt)
        pullf_free(pkt);

    if (src)
        pullf_free(src);

    if (res < 0)
        return res;

    /*
     * Report a failure of the prefix_init() "quick check" now, rather than
     * upon detection, to hinder timing attacks.  pgcrypto is not generally
     * secure against timing attacks, but this helps.
     */
    if (!got_data || ctx->corrupt_prefix)
        return PXE_PGP_CORRUPT_DATA;

    /*
     * Code interpreting purportedly-decrypted data prior to this stage shall
     * report no error other than PXE_PGP_CORRUPT_DATA.  (PXE_BUG is okay so
     * long as it remains unreachable.)  This ensures that an attacker able to
     * choose a ciphertext and receive a corresponding decryption error
     * message cannot use that oracle to gather clues about the decryption
     * key.  See "An Attack on CFB Mode Encryption As Used By OpenPGP" by
     * Serge Mister and Robert Zuccherato.
     *
     * A problematic value in the first octet of a Literal Data or Compressed
     * Data packet may indicate a simple user error, such as the need to call
     * pgp_sym_decrypt_bytea instead of pgp_sym_decrypt.  Occasionally,
     * though, it is the first symptom of the encryption key not matching the
     * decryption key.  When this was the only problem encountered, report a
     * specific error to guide the user; otherwise, we will have reported
     * PXE_PGP_CORRUPT_DATA before now.  A key mismatch makes the other errors
     * into red herrings, and this avoids leaking clues to attackers.
     */
    if (ctx->unsupported_compr)
        return PXE_PGP_UNSUPPORTED_COMPR;
    if (ctx->unexpected_binary)
        return PXE_PGP_NOT_TEXT;

    return res;
}