gpgme_funcs.c

/*
 *****************************************************************************
 *
 * File:    gpgme_funcs.c
 *
 * Author:  Damien S. Stuart
 *
 * Purpose: gpgme-related functions for GPG encryptions support in libfko.
 *
 * Copyright 2009-2010 Damien Stuart (dstuart@dstuart.org)
 *
 *  License (GNU Public License):
 *
 *  This program 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 2
 *  of the License, or (at your option) any later version.
 *
 *  This program 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
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
 *  USA
 *
 *****************************************************************************
*/

#include "fko_common.h"
#include "fko.h"

#if HAVE_LIBGPGME
#include "gpgme_funcs.h"

int
init_gpgme(fko_ctx_t fko_ctx)
{
    gpgme_error_t       err;

    /* If we already have a context, we are done.
    */
    if(fko_ctx->have_gpgme_context)
        return(FKO_SUCCESS);

    /* Because the gpgme manual says you should.
    */
    gpgme_check_version(NULL);

    /* Check for OpenPGP support
    */
    err = gpgme_engine_check_version(GPGME_PROTOCOL_OpenPGP);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        /* GPG engine is not available.
        */
        fko_ctx->gpg_err = err;
        return(FKO_ERROR_GPGME_NO_OPENPGP);
    }

    /* Extract the current gpgme engine information.
    */
    gpgme_set_engine_info(
            GPGME_PROTOCOL_OpenPGP,
            (fko_ctx->gpg_exe != NULL) ? fko_ctx->gpg_exe : GPG_EXE,
            fko_ctx->gpg_home_dir   /* If this is NULL, the default is used */
    );

    /* Create our gpgme context
    */
    err = gpgme_new(&(fko_ctx->gpg_ctx));
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        fko_ctx->gpg_err = err;
        return(FKO_ERROR_GPGME_CONTEXT);
    }

    fko_ctx->have_gpgme_context = 1;

    return(FKO_SUCCESS);
}

/* Callback function that supplies the password when gpgme needs it.
*/
gpgme_error_t
my_passphrase_cb(
  void *pw, const char *uid_hint, const char *passphrase_info,
  int prev_was_bad, int fd)
{
    /* We only need to try once as it is fed by the program
     * (for now --DSS).
    */
    if(prev_was_bad)
        return(GPG_ERR_CANCELED);

    if(write(fd, (const char*)pw, strlen((const char*)pw))
      != strlen((const char*)pw))
        return(GPG_ERR_SYSTEM_ERROR); /* Must be a GPG error, but which one? */

    if(write(fd, "\n", 1) != 1)
        return(GPG_ERR_SYSTEM_ERROR); /* Must be a GPG error, but which one? */

    return 0;
}

/* Verify gpg signatures in a verify_result set.
*/
int
process_sigs(fko_ctx_t fko_ctx, gpgme_verify_result_t vres)
{
    unsigned int        sig_cnt = 0;
    gpgme_signature_t   sig     = vres->signatures;
    fko_gpg_sig_t       fgs;

    /* only want to see one signature (for now).
    */
    if(!sig)
        return(FKO_ERROR_GPGME_NO_SIGNATURE);

    /* Iterate over the sigs and store the info we are interested in
     * to the context.
     *
     * NOTE: At present, we support only a single signature.  However,
     *       that may change in a future release.  We go a head and
     *       grab all signatures even though we will only use the first
     *       one.  --DSS
    */
    while(sig != NULL)
    {
        fgs = calloc(1, sizeof(struct fko_gpg_sig));
        if(fgs == NULL)
            return(FKO_ERROR_MEMORY_ALLOCATION);

        /* Grab the summary and status values.
        */
        fgs->summary    = sig->summary;
        fgs->status     = sig->status;
        fgs->validity   = sig->validity;

        /* Grab the signature fingerprint.
        */
        if(sig->fpr != NULL)
        {
            fgs->fpr = strdup(sig->fpr);
            if(fgs->fpr == NULL)
            {
                free(fgs);
                return(FKO_ERROR_MEMORY_ALLOCATION);
            }
        }

        if(sig_cnt == 0)
            fko_ctx->gpg_sigs = fgs;
        else
            fko_ctx->gpg_sigs->next = fgs;

        sig_cnt++;
        sig = sig->next;
    }

    /* If we are ignoring bad signatures, return success here.
    */
    if(fko_ctx->ignore_gpg_sig_error != 0)
        return(FKO_SUCCESS);

    /* Otherwise, we check them here and respond accordingly.
    */
    fgs = fko_ctx->gpg_sigs;

    if(fgs->status != GPG_ERR_NO_ERROR || fgs->validity < 3) {
        fko_ctx->gpg_err = fgs->status;

        return(FKO_ERROR_GPGME_BAD_SIGNATURE);
    }

    return(FKO_SUCCESS);
}

/* Get the GPG key for the given name or ID.
*/
int
get_gpg_key(fko_ctx_t fko_ctx, gpgme_key_t *mykey, const int signer)
{
    int             res;
    const char     *name;

    gpgme_ctx_t     list_ctx    = NULL;
    gpgme_key_t     key         = NULL;
    gpgme_key_t     key2        = NULL;
    gpgme_error_t   err;

    /* Create a gpgme context for the list
    */
    /* Initialize gpgme
    */
    res = init_gpgme(fko_ctx);
    if(res != FKO_SUCCESS)
    {
        if(signer)
            return(FKO_ERROR_GPGME_CONTEXT_SIGNER_KEY);
        else
            return(FKO_ERROR_GPGME_CONTEXT_RECIPIENT_KEY);
    }

    list_ctx = fko_ctx->gpg_ctx;

    if(signer)
        name = fko_ctx->gpg_signer;
    else
        name = fko_ctx->gpg_recipient;

    err = gpgme_op_keylist_start(list_ctx, name, signer);
    if (err)
    {
        gpgme_release(list_ctx);

        fko_ctx->gpg_err = err;

        if(signer)
            return(FKO_ERROR_GPGME_SIGNER_KEYLIST_START);
        else
            return(FKO_ERROR_GPGME_RECIPIENT_KEYLIST_START);
    }

    /* Grab the first key in the list (we hope it is the only one).
    */
    err = gpgme_op_keylist_next(list_ctx, &key);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        /* Key not found
        */
        fko_ctx->gpg_err = err;

        if(signer)
            return(FKO_ERROR_GPGME_SIGNER_KEY_NOT_FOUND);
        else
            return(FKO_ERROR_GPGME_RECIPIENT_KEY_NOT_FOUND);
    }

    /* We try to get the next key match. If we do, then the name is
     * ambiguous, so we return an error.
    */
    err = gpgme_op_keylist_next(list_ctx, &key2);
    if(gpg_err_code(err) == GPG_ERR_NO_ERROR) /* Note: look for NO error */
    {
        /* Ambiguous specfication of key
        */
        gpgme_key_unref(key);
        gpgme_key_unref(key2);

        fko_ctx->gpg_err = err;

        if(signer)
            return(FKO_ERROR_GPGME_SIGNER_KEY_AMBIGUOUS);
        else
            return(FKO_ERROR_GPGME_RECIPIENT_KEY_AMBIGUOUS);
    }

    gpgme_op_keylist_end(list_ctx);

    gpgme_key_unref(key2);

    *mykey = key;

    return(FKO_SUCCESS);
}

/* The main GPG encryption routine for libfko.
*/
int
gpgme_encrypt(fko_ctx_t fko_ctx, unsigned char *indata, size_t in_len, const char *pw, unsigned char **out, size_t *out_len)
{
    char               *tmp_buf;
    int                 res;

    gpgme_ctx_t         gpg_ctx     = NULL;
    gpgme_data_t        cipher      = NULL;
    gpgme_data_t        plaintext   = NULL;
    gpgme_key_t         key[2]      = { NULL, NULL };
    gpgme_error_t       err;

    /* Initialize gpgme
    */
    res = init_gpgme(fko_ctx);
    if(res != FKO_SUCCESS)
        return(res);

    gpg_ctx = fko_ctx->gpg_ctx;

    /* Initialize the plaintext data (place into gpgme_data object)
    */
    err = gpgme_data_new_from_mem(&plaintext, (char*)indata, in_len, 1);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;
        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_PLAINTEXT_DATA_OBJ);
    }

    /* Set protocol
    */
    err = gpgme_set_protocol(gpg_ctx, GPGME_PROTOCOL_OpenPGP);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_data_release(plaintext);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_SET_PROTOCOL);
    }

    /* Set ascii-armor off (we will be base64-encoding the encrypted data
     * ourselves.
    */
    gpgme_set_armor(gpg_ctx, 0);

    /* The gpgme_encrypt.... functions take a recipient key array, so we add
     * our single key here.
    */
    key[0] = fko_ctx->recipient_key;

    /* Create the buffer for our encrypted data.
    */
    err = gpgme_data_new(&cipher);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_data_release(plaintext);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_CIPHER_DATA_OBJ);
    }

    /* Here we add the signer to the gpgme context if there is one.
    */
    if(fko_ctx->gpg_signer != NULL) {
        gpgme_signers_clear(gpg_ctx);
        err = gpgme_signers_add(gpg_ctx, fko_ctx->signer_key);
        if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
        {
            gpgme_data_release(plaintext);
            gpgme_data_release(cipher);
            gpgme_release(gpg_ctx);
            fko_ctx->gpg_ctx = NULL;

            fko_ctx->gpg_err = err;

            return(FKO_ERROR_GPGME_ADD_SIGNER);
        }
    }

    /* Set the passphrase callback.
    */
    gpgme_set_passphrase_cb(gpg_ctx, my_passphrase_cb, (void*)pw);

    /* Encrypt and sign (if a sig was provided) the SPA data.
    */
    if(fko_ctx->gpg_signer == NULL)
        err = gpgme_op_encrypt(
            gpg_ctx, key, GPGME_ENCRYPT_ALWAYS_TRUST, plaintext, cipher
        );
    else
        err = gpgme_op_encrypt_sign(
            gpg_ctx, key, GPGME_ENCRYPT_ALWAYS_TRUST, plaintext, cipher
        );

    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_data_release(plaintext);
        gpgme_data_release(cipher);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        if(gpgme_err_code(err) == GPG_ERR_CANCELED)
            return(FKO_ERROR_GPGME_BAD_PASSPHRASE);

        return(FKO_ERROR_GPGME_ENCRYPT_SIGN);
    }

    /* Done with the plaintext.
    */
    gpgme_data_release(plaintext);

    /* Get the encrypted data and its length from the gpgme data object.
     * BTW, this does does free the memory used by cipher.
    */
    tmp_buf = gpgme_data_release_and_get_mem(cipher, out_len);

    *out = malloc(*out_len); /* This is freed upon fko_ctx destruction. */
    if(*out == NULL)
        res = FKO_ERROR_MEMORY_ALLOCATION;
    else
    {
        memcpy(*out, tmp_buf, *out_len);
        res = FKO_SUCCESS;
    }

    gpgme_free(tmp_buf);

    return(res);
}

/* The main GPG decryption routine for libfko.
*/
int
gpgme_decrypt(fko_ctx_t fko_ctx, unsigned char *indata, size_t in_len, const char *pw, unsigned char **out, size_t *out_len)
{
    char                   *tmp_buf;
    int                     res;

    gpgme_ctx_t             gpg_ctx     = NULL;
    gpgme_data_t            cipher      = NULL;
    gpgme_data_t            plaintext   = NULL;
    gpgme_error_t           err;
    gpgme_decrypt_result_t  decrypt_res;
    gpgme_verify_result_t   verify_res;

    /* Initialize gpgme
    */
    res = init_gpgme(fko_ctx);
    if(res != FKO_SUCCESS)
        return(res);

    gpg_ctx = fko_ctx->gpg_ctx;

    err = gpgme_data_new(&plaintext);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_PLAINTEXT_DATA_OBJ);
    }

    /* Initialize the cipher data (place into gpgme_data object)
    */
    err = gpgme_data_new_from_mem(&cipher, (char*)indata, in_len, 0);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_data_release(plaintext);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_CIPHER_DATA_OBJ);
    }

    /* Set the passphrase callback.
    */
    gpgme_set_passphrase_cb(gpg_ctx, my_passphrase_cb, (void*)pw);

    /* Now decrypt and verify.
    */
    err = gpgme_op_decrypt_verify(gpg_ctx, cipher, plaintext);
    if(gpg_err_code(err) != GPG_ERR_NO_ERROR)
    {
        gpgme_data_release(plaintext);
        gpgme_data_release(cipher);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        fko_ctx->gpg_err = err;

        return(FKO_ERROR_GPGME_DECRYPT_FAILED);
    }

    /* Done with the cipher text.
    */
    gpgme_data_release(cipher);

    /* We check the "usupported_algorithm" flag in the decrypt result.
    */
    decrypt_res = gpgme_op_decrypt_result(gpg_ctx);

    if(decrypt_res->unsupported_algorithm)
    {
        gpgme_data_release(plaintext);
        gpgme_release(gpg_ctx);
        fko_ctx->gpg_ctx = NULL;

        return(FKO_ERROR_GPGME_DECRYPT_UNSUPPORTED_ALGORITHM);
    }

    /* Now verify the signatures if so configured.
    */
    if(fko_ctx->verify_gpg_sigs)
    {
        verify_res  = gpgme_op_verify_result(gpg_ctx);

        res = process_sigs(fko_ctx, verify_res);

        if(res != FKO_SUCCESS)
        {
            gpgme_data_release(plaintext);
            gpgme_release(gpg_ctx);
            fko_ctx->gpg_ctx = NULL;

            return(res);
        }
    }

    /* Get the encrypted data and its length from the gpgme data object.
    */
    tmp_buf = gpgme_data_release_and_get_mem(plaintext, out_len);

    /* Use calloc here with an extra byte because I am not sure if all systems
     * will include the terminating NULL with the decrypted data (which is
     * expected to be a string).
    */
    *out = calloc(1, *out_len+1); /* This is freed upon fko_ctx destruction. */

    if(*out == NULL)
        res = FKO_ERROR_MEMORY_ALLOCATION;
    else
    {
        memcpy(*out, tmp_buf, *out_len);
        res = FKO_SUCCESS;
    }

    gpgme_free(tmp_buf);

    return(res);
}

#endif /* HAVE_LIBGPGME */

/***EOF***/