common/libntfs/crypto.c

/**
 * crypto.c - Routines for dealing with encrypted files.  Part of the
 *            Linux-NTFS project.
 *
 * Copyright (c) 2005      Yuval Fledel
 * Copyright (c) 2005-2007 Anton Altaparmakov
 * Copyright (c) 2007      Yura Pakhuchiy
 *
 * 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 (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * TODO: Cleanup this file. Write nice descriptions for non-exported functions
 * and maybe clean up namespace (not necessary for all functions to belong to
 * ntfs_crypto, we can have ntfs_fek, ntfs_rsa, etc.., but there should be
 * maximum 2-3 namespaces, not every function begins with it own namespace
 * like now).
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef HAVE_STDIO_H
#include <stdio.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif

#include "compat.h"
#include "attrib.h"
#include "types.h"
#include "volume.h"
#include "debug.h"
#include "dir.h"
#include "layout.h"
#include "crypto.h"

#ifdef ENABLE_CRYPTO

#include <gcrypt.h>
#include <gnutls/pkcs12.h>
#include <gnutls/x509.h>

#include <libconfig.h>

#define NTFS_CONFIG_PATH_SYSTEM     "/etc/libntfs/config"
#define NTFS_CONFIG_PATH_USER       ".libntfs/config"

#define NTFS_SHA1_THUMBPRINT_SIZE   0x14

#define NTFS_CRED_TYPE_CERT_THUMBPRINT  const_cpu_to_le32(3)

#define NTFS_EFS_CERT_PURPOSE_OID_DDF   "1.3.6.1.4.1.311.10.3.4"
#define NTFS_EFS_CERT_PURPOSE_OID_DRF   "1.3.6.1.4.1.311.10.3.4.1"

#define NTFS_EFS_SECTOR_SIZE        512

typedef enum {
    DF_TYPE_UNKNOWN,
    DF_TYPE_DDF,
    DF_TYPE_DRF,
} NTFS_DF_TYPES;

/**
 * enum NTFS_CRYPTO_ALGORITHMS - List of crypto algorithms used by EFS (32 bit)
 *
 * To choose which one is used in Windows, create or set the REG_DWORD registry
 * key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\EFS\
 * AlgorithmID to the value of your chosen crypto algorithm, e.g. to use DesX,
 * set AlgorithmID to 0x6604.
 *
 * Note that the Windows versions I have tried so far (all are high crypto
 * enabled) ignore the AlgorithmID value if it is not one of CALG_3DES,
 * CALG_DESX, or CALG_AES_256, i.e. you cannot select CALG_DES at all using
 * this registry key.  It would be interesting to check out encryption on one
 * of the "crippled" crypto Windows versions...
 */
typedef enum {
    CALG_DES    = const_cpu_to_le32(0x6601),
    /* If not one of the below three, fall back to standard Des. */
    CALG_3DES   = const_cpu_to_le32(0x6603),
    CALG_DESX   = const_cpu_to_le32(0x6604),
    CALG_AES_256    = const_cpu_to_le32(0x6610),
} NTFS_CRYPTO_ALGORITHMS;

/**
 * struct ntfs_fek - Decrypted, in-memory file encryption key.
 */
struct _ntfs_fek {
    gcry_cipher_hd_t gcry_cipher_hd;
    le32 alg_id;
    u8 *key_data;
    gcry_cipher_hd_t *des_gcry_cipher_hd_ptr;
};

typedef struct _ntfs_fek ntfs_fek;

struct _ntfs_crypto_attr {
    ntfs_fek *fek;
};

typedef struct {
    u64 in_whitening, out_whitening;
    gcry_cipher_hd_t gcry_cipher_hd;
} ntfs_desx_ctx;

ntfschar NTFS_EFS[5] = {
    const_cpu_to_le16('$'), const_cpu_to_le16('E'), const_cpu_to_le16('F'),
    const_cpu_to_le16('S'), const_cpu_to_le16(0)
};

typedef struct {
    gcry_sexp_t key;
    NTFS_DF_TYPES df_type;
    char thumbprint[NTFS_SHA1_THUMBPRINT_SIZE];
} ntfs_rsa_private_key_t;

/*
 * Yes, global variables sucks, but we need to keep whether we performed
 * gcrypt/gnutls global initialization and keep user's RSA keys.
 */
typedef struct {
    int initialized;
    int desx_alg_id;
    gcry_module_t desx_module;
    ntfs_rsa_private_key_t **rsa_key;
    int nr_rsa_keys;
} ntfs_crypto_ctx_t;

static ntfs_crypto_ctx_t ntfs_crypto_ctx = {
    .desx_alg_id = -1,
    .desx_module = NULL,
};

/**
 * ntfs_pkcs12_load_pfxfile
 */
static int ntfs_pkcs12_load_pfxfile(const char *keyfile, u8 **pfx,
        unsigned *pfx_size)
{
    int f, to_read, total, attempts, br;
    struct stat key_stat;

    if (!keyfile || !pfx || !pfx_size) {
        ntfs_log_error("You have to specify the key file, a pointer "
                "to hold the key file contents, and a pointer "
                "to hold the size of the key file contents.\n");
        return -1;
    }
    f = open(keyfile, O_RDONLY);
    if (f == -1) {
        ntfs_log_perror("Failed to open key file");
        return -1;
    }
    if (fstat(f, &key_stat) == -1) {
        ntfs_log_perror("Failed to stat key file");
        goto file_out;
    }
    if (!S_ISREG(key_stat.st_mode)) {
        ntfs_log_error("Key file is not a regular file, cannot read "
                "it.\n");
        goto file_out;
    }
    if (!key_stat.st_size) {
        ntfs_log_error("Key file has zero size.\n");
        goto file_out;
    }
    *pfx = malloc(key_stat.st_size + 1);
    if (!*pfx) {
        ntfs_log_perror("Failed to allocate buffer for key file "
            "contents");
        goto file_out;
    }
    to_read = key_stat.st_size;
    total = attempts = 0;
    do {
        br = read(f, *pfx + total, to_read);
        if (br == -1) {
            ntfs_log_perror("Failed to read from key file");
            goto free_out;
        }
        if (!br)
            attempts++;
        to_read -= br;
        total += br;
    } while (to_read > 0 && attempts < 3);
    close(f);
    /* Make sure it is zero terminated. */
    (*pfx)[key_stat.st_size] = 0;
    *pfx_size = key_stat.st_size;
    return 0;
free_out:
    free(*pfx);
file_out:
    close(f);
    return -1;
}

/**
 * ntfs_rsa_private_key_import_from_gnutls
 */
static gcry_sexp_t ntfs_rsa_private_key_import_from_gnutls(
        gnutls_x509_privkey_t priv_key)
{
    int i, j;
    size_t tmp_size;
    gnutls_datum_t rd[6];
    gcry_mpi_t rm[6];
    gcry_sexp_t rsa_key;

    /* Extract the RSA parameters from the GNU TLS private key. */
    if (gnutls_x509_privkey_export_rsa_raw(priv_key, &rd[0], &rd[1],
            &rd[2], &rd[3], &rd[4], &rd[5])) {
        ntfs_log_error("Failed to export rsa parameters.  (Is the "
                "key an RSA private key?)\n");
        return NULL;
    }
    /* Convert each RSA parameter to MPI format. */
    for (i = 0; i < 6; i++) {
        if (gcry_mpi_scan(&rm[i], GCRYMPI_FMT_USG, rd[i].data,
                rd[i].size, &tmp_size) != GPG_ERR_NO_ERROR) {
            ntfs_log_error("Failed to convert RSA parameter %i "
                    "to mpi format (size %d)\n", i,
                    rd[i].size);
            rsa_key = NULL;
            break;
        }
    }
    /* Release the no longer needed datum values. */
    for (j = 0; j < 6; j++) {
        if (rd[j].data && rd[j].size)
            gnutls_free(rd[j].data);
    }
    /*
     * Build the gcrypt private key, note libgcrypt uses p and q inversed
     * to what gnutls uses.
     */
    if (i == 6 && gcry_sexp_build(&rsa_key, NULL,
            "(private-key(rsa(n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))",
            rm[0], rm[1], rm[2], rm[4], rm[3], rm[5]) !=
            GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to build RSA private key s-exp.\n");
        rsa_key = NULL;
    }
    /* Release the no longer needed MPI values. */
    for (j = 0; j < i; j++)
        gcry_mpi_release(rm[j]);
    return rsa_key;
}

/**
 * ntfs_rsa_private_key_release
 */
static void ntfs_rsa_private_key_release(ntfs_rsa_private_key_t *rsa_key)
{
    if (rsa_key) {
        if (rsa_key->key)
            gcry_sexp_release(rsa_key->key);
        free(rsa_key);
    }
}

/**
 * ntfs_pkcs12_extract_rsa_key
 */
static ntfs_rsa_private_key_t *ntfs_pkcs12_extract_rsa_key(u8 *pfx,
        int pfx_size, const char *password)
{
    int err, bag_index, flags;
    gnutls_datum_t dpfx, dkey;
    gnutls_pkcs12_t pkcs12 = NULL;
    gnutls_pkcs12_bag_t bag = NULL;
    gnutls_x509_privkey_t pkey = NULL;
    gnutls_x509_crt_t crt = NULL;
    ntfs_rsa_private_key_t *rsa_key = NULL;
    char purpose_oid[100];
    size_t purpose_oid_size = sizeof(purpose_oid);
    size_t tp_size;
    BOOL have_thumbprint = FALSE;

    rsa_key = malloc(sizeof(ntfs_rsa_private_key_t));
    if (!rsa_key) {
        ntfs_log_perror("%s", "ntfs_pkcs12_extract_rsa_key");
        return NULL;
    }
    rsa_key->df_type = DF_TYPE_UNKNOWN;
    rsa_key->key = NULL;
    tp_size = sizeof(rsa_key->thumbprint);
    /* Create a pkcs12 structure. */
    err = gnutls_pkcs12_init(&pkcs12);
    if (err) {
        ntfs_log_error("Failed to initialize PKCS#12 structure: %s\n",
                gnutls_strerror(err));
        goto err;
    }
    /* Convert the PFX file (DER format) to native pkcs12 format. */
    dpfx.data = pfx;
    dpfx.size = pfx_size;
    err = gnutls_pkcs12_import(pkcs12, &dpfx, GNUTLS_X509_FMT_DER, 0);
    if (err) {
        ntfs_log_error("Failed to convert the PFX file from DER to "
                "native PKCS#12 format: %s\n",
                gnutls_strerror(err));
        goto err;
    }
    /*
     * Verify that the password is correct and that the key file has not
     * been tampered with.  Note if the password has zero length and the
     * verification fails, retry with password set to NULL.  This is needed
     * to get password less .pfx files generated with Windows XP SP1 (and
     * probably earlier versions of Windows) to work.
     */
retry_verify:
    err = gnutls_pkcs12_verify_mac(pkcs12, password);
    if (err) {
        if (err == GNUTLS_E_MAC_VERIFY_FAILED &&
                password && !strlen(password)) {
            password = NULL;
            goto retry_verify;
        }
        ntfs_log_error("You are probably misspelled password to PFX "
                "file.\n");
        goto err;
    }
    for (bag_index = 0; ; bag_index++) {
        err = gnutls_pkcs12_bag_init(&bag);
        if (err) {
            ntfs_log_error("Failed to initialize PKCS#12 Bag "
                    "structure: %s\n",
                    gnutls_strerror(err));
            goto err;
        }
        err = gnutls_pkcs12_get_bag(pkcs12, bag_index, bag);
        if (err) {
            if (err == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
                err = 0;
                break;
            }
            ntfs_log_error("Failed to obtain Bag from PKCS#12 "
                    "structure: %s\n",
                    gnutls_strerror(err));
            goto err;
        }
check_again:
        err = gnutls_pkcs12_bag_get_count(bag);
        if (err < 0) {
            ntfs_log_error("Failed to obtain Bag count: %s\n",
                    gnutls_strerror(err));
            goto err;
        }
        err = gnutls_pkcs12_bag_get_type(bag, 0);
        if (err < 0) {
            ntfs_log_error("Failed to determine Bag type: %s\n",
                    gnutls_strerror(err));
            goto err;
        }
        flags = 0;
        switch (err) {
        case GNUTLS_BAG_PKCS8_KEY:
            flags = GNUTLS_PKCS_PLAIN;
        case GNUTLS_BAG_PKCS8_ENCRYPTED_KEY:
            err = gnutls_pkcs12_bag_get_data(bag, 0, &dkey);
            if (err < 0) {
                ntfs_log_error("Failed to obtain Bag data: "
                        "%s\n", gnutls_strerror(err));
                goto err;
            }
            err = gnutls_x509_privkey_init(&pkey);
            if (err) {
                ntfs_log_error("Failed to initialized "
                        "private key structure: %s\n",
                        gnutls_strerror(err));
                goto err;
            }
            /* Decrypt the private key into GNU TLS format. */
            err = gnutls_x509_privkey_import_pkcs8(pkey, &dkey,
                    GNUTLS_X509_FMT_DER, password, flags);
            if (err) {
                ntfs_log_error("Failed to convert private "
                        "key from DER to GNU TLS "
                        "format: %s\n",
                        gnutls_strerror(err));
                goto err;
            }
#if 0
            /*
             * Export the key again, but unencrypted, and output it
             * to stderr.  Note the output has an RSA header so to
             * compare to openssl pkcs12 -nodes -in myfile.pfx
             * output need to ignore the part of the key between
             * the first "MII..." up to the second "MII...".  The
             * actual RSA private key begins at the second "MII..."
             * and in my testing at least was identical to openssl
             * output and was also identical both on big and little
             * endian so gnutls should be endianness safe.
             */
            char *buf = malloc(8192);
            size_t bufsize = 8192;
            err = gnutls_x509_privkey_export_pkcs8(pkey,
                GNUTLS_X509_FMT_PEM, "", GNUTLS_PKCS_PLAIN, buf,
                &bufsize);
            if (err) {
                ntfs_log_error("eek1\n");
                exit(1);
            }
            ntfs_log_error("%s\n", buf);
            free(buf);
#endif
            /* Convert the private key to our internal format. */
            rsa_key->key =
                ntfs_rsa_private_key_import_from_gnutls(pkey);
            if (!rsa_key->key)
                goto err;
            break;
        case GNUTLS_BAG_ENCRYPTED:
            err = gnutls_pkcs12_bag_decrypt(bag, password);
            if (err) {
                ntfs_log_error("Failed to decrypt Bag: %s\n",
                        gnutls_strerror(err));
                goto err;
            }
            goto check_again;
        case GNUTLS_BAG_CERTIFICATE:
            err = gnutls_pkcs12_bag_get_data(bag, 0, &dkey);
            if (err < 0) {
                ntfs_log_error("Failed to obtain Bag data: "
                        "%s\n", gnutls_strerror(err));
                goto err;
            }
            err = gnutls_x509_crt_init(&crt);
            if (err) {
                ntfs_log_error("Failed to initialize "
                        "certificate structure: %s\n",
                        gnutls_strerror(err));
                goto err;
            }
            err = gnutls_x509_crt_import(crt, &dkey,
                    GNUTLS_X509_FMT_DER);
            if (err) {
                ntfs_log_error("Failed to convert certificate "
                        "from DER to GNU TLS format: "
                        "%s\n", gnutls_strerror(err));
                goto err;
            }
            err = gnutls_x509_crt_get_key_purpose_oid(crt, 0,
                    purpose_oid, &purpose_oid_size, NULL);
            if (err) {
                ntfs_log_error("Failed to get key purpose "
                        "OID: %s\n",
                        gnutls_strerror(err));
                goto err;
            }
            purpose_oid[purpose_oid_size - 1] = 0;
            if (!strcmp(purpose_oid,
                    NTFS_EFS_CERT_PURPOSE_OID_DRF))
                rsa_key->df_type = DF_TYPE_DRF;
            else if (!strcmp(purpose_oid,
                    NTFS_EFS_CERT_PURPOSE_OID_DDF))
                rsa_key->df_type = DF_TYPE_DDF;
            else {
                ntfs_log_error("Certificate has unknown "
                        "purpose OID %s.\n",
                        purpose_oid);
                err = EINVAL;
                goto err;
            }
            /* Return the thumbprint to the caller. */
            err = gnutls_x509_crt_get_fingerprint(crt,
                    GNUTLS_DIG_SHA1, rsa_key->thumbprint,
                    &tp_size);
            if (err) {
                ntfs_log_error("Failed to get thumbprint: "
                        "%s\n", gnutls_strerror(err));
                goto err;
            }
            if (tp_size != NTFS_SHA1_THUMBPRINT_SIZE) {
                ntfs_log_error("Invalid thumbprint size %zd.  "
                        "Should be %d.\n", tp_size,
                        sizeof(rsa_key->thumbprint));
                err = EINVAL;
                goto err;
            }
            have_thumbprint = TRUE;
            gnutls_x509_crt_deinit(crt);
            crt = NULL;
            break;
        default:
            /* We do not care about other types. */
            break;
        }
        gnutls_pkcs12_bag_deinit(bag);
    }
err:
    if (err || !rsa_key->key || rsa_key->df_type == DF_TYPE_UNKNOWN ||
            !have_thumbprint) {
        if (!err)
            ntfs_log_error("Key type or thumbprint not found, "
                    "aborting.\n");
        ntfs_rsa_private_key_release(rsa_key);
        rsa_key = NULL;
    }
    if (crt)
        gnutls_x509_crt_deinit(crt);
    if (pkey)
        gnutls_x509_privkey_deinit(pkey);
    if (bag)
        gnutls_pkcs12_bag_deinit(bag);
    if (pkcs12)
        gnutls_pkcs12_deinit(pkcs12);
    return rsa_key;
}

/**
 * ntfs_buffer_reverse -
 *
 * This is a utility function for reversing the order of a buffer in place.
 * Users of this function should be very careful not to sweep byte order
 * problems under the rug.
 */
static inline void ntfs_buffer_reverse(u8 *buf, unsigned buf_size)
{
    unsigned i;
    u8 t;

    for (i = 0; i < buf_size / 2; i++) {
        t = buf[i];
        buf[i] = buf[buf_size - i - 1];
        buf[buf_size - i - 1] = t;
    }
}

#ifndef HAVE_STRNLEN
/**
 * strnlen - strnlen is a gnu extension so emulate it if not present
 */
static size_t strnlen(const char *s, size_t maxlen)
{
    const char *p, *end;

    /* Look for a '\0' character. */
    for (p = s, end = s + maxlen; p < end && *p; p++)
        ;
    return p - s;
}
#endif /* ! HAVE_STRNLEN */

/**
 * ntfs_raw_fek_decrypt -
 *
 * Note: decrypting into the input buffer.
 */
static unsigned ntfs_raw_fek_decrypt(u8 *fek, u32 fek_size,
        ntfs_rsa_private_key_t *rsa_key)
{
    gcry_mpi_t fek_mpi;
    gcry_sexp_t fek_sexp, fek_sexp2;
    gcry_error_t err;
    size_t size, padding;

    /* Reverse the raw FEK. */
    ntfs_buffer_reverse(fek, fek_size);
    /* Convert the FEK to internal MPI format. */
    err = gcry_mpi_scan(&fek_mpi, GCRYMPI_FMT_USG, fek, fek_size, NULL);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to convert file encryption key to "
                "internal MPI format: %s\n",
                gcry_strerror(err));
        return 0;
    }
    /* Create an internal S-expression from the FEK. */
    err = gcry_sexp_build(&fek_sexp, NULL,
            "(enc-val (flags) (rsa (a %m)))", fek_mpi);
    gcry_mpi_release(fek_mpi);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to create internal S-expression of "
                "the file encryption key: %s\n",
                gcry_strerror(err));
        return 0;
    }
    /* Decrypt the FEK. */
    err = gcry_pk_decrypt(&fek_sexp2, fek_sexp, rsa_key->key);
    gcry_sexp_release(fek_sexp);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to decrypt the file encryption key: "
                "%s\n", gcry_strerror(err));
        return 0;
    }
    /* Extract the actual FEK from the decrypted raw S-expression. */
    fek_sexp = gcry_sexp_find_token(fek_sexp2, "value", 0);
    gcry_sexp_release(fek_sexp2);
    if (!fek_sexp) {
        ntfs_log_error("Failed to find the decrypted file encryption "
                "key in the internal S-expression.\n");
        return 0;
    }
    /* Convert the decrypted FEK S-expression into MPI format. */
    fek_mpi = gcry_sexp_nth_mpi(fek_sexp, 1, GCRYMPI_FMT_USG);
    gcry_sexp_release(fek_sexp);
    if (!fek_mpi) {
        ntfs_log_error("Failed to convert the decrypted file "
                "encryption key S-expression to internal MPI "
                "format.\n");
        return 0;
    }
    /* Convert the decrypted FEK from MPI format to binary data. */
    err = gcry_mpi_print(GCRYMPI_FMT_USG, fek, fek_size, &size, fek_mpi);
    gcry_mpi_release(fek_mpi);
    if (err != GPG_ERR_NO_ERROR || !size) {
        ntfs_log_error("Failed to convert decrypted file encryption "
                "key from internal MPI format to binary data: "
                "%s\n", gcry_strerror(err));
        return 0;
    }
    /*
     * Finally, remove the PKCS#1 padding and return the size of the
     * decrypted FEK.
     */
    padding = strnlen((char *)fek, size) + 1;
    if (padding > size) {
        ntfs_log_error("Failed to remove PKCS#1 padding from "
                "decrypted file encryption key.\n");
        return 0;
    }
    size -= padding;
    memmove(fek, fek + padding, size);
    return size;
}

/**
 * ntfs_desx_key_expand - expand a 128-bit desx key to the needed 192-bit key
 * @src:    source buffer containing 128-bit key
 *
 * Expands the on-disk 128-bit desx key to the needed des key, the in-, and the
 * out-whitening keys required to perform desx {de,en}cryption.
 */
static gcry_error_t ntfs_desx_key_expand(const u8 *src, u32 *des_key,
        u64 *out_whitening, u64 *in_whitening)
{
    static const u8 *salt1 = (const u8*)"Dan Simon  ";
    static const u8 *salt2 = (const u8*)"Scott Field";
    static const int salt_len = 12;
    gcry_md_hd_t hd1, hd2;
    u32 *md;
    gcry_error_t err;

    err = gcry_md_open(&hd1, GCRY_MD_MD5, 0);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to open MD5 digest.\n");
        return err;
    }
    /* Hash the on-disk key. */
    gcry_md_write(hd1, src, 128 / 8);
    /* Copy the current hash for efficiency. */
    err = gcry_md_copy(&hd2, hd1);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to copy MD5 digest object.\n");
        goto out;
    }
    /* Hash with the first salt and store the result. */
    gcry_md_write(hd1, salt1, salt_len);
    md = (u32*)gcry_md_read(hd1, 0);
    des_key[0] = md[0] ^ md[1];
    des_key[1] = md[2] ^ md[3];
    /* Hash with the second salt and store the result. */
    gcry_md_write(hd2, salt2, salt_len);
    md = (u32*)gcry_md_read(hd2, 0);
    *out_whitening = *(u64*)md;
    *in_whitening = *(u64*)(md + 2);
    gcry_md_close(hd2);
out:
    gcry_md_close(hd1);
    return err;
}

/**
 * ntfs_desx_setkey - libgcrypt set_key implementation for DES-X-MS128
 * @context:    pointer to a variable of type ntfs_desx_ctx
 * @key:    the 128 bit DES-X-MS128 key, concated with the DES handle
 * @keylen: must always be 16
 *
 * This is the libgcrypt set_key implementation for DES-X-MS128.
 */
static gcry_err_code_t ntfs_desx_setkey(void *context, const u8 *key,
        unsigned keylen)
{
    ntfs_desx_ctx *ctx = context;
    gcry_error_t err;
    u8 des_key[8];

    if (keylen != 16) {
        ntfs_log_error("Key length for desx must be 16.\n");
        return GPG_ERR_INV_KEYLEN;
    }
    err = gcry_cipher_open(&ctx->gcry_cipher_hd, GCRY_CIPHER_DES,
            GCRY_CIPHER_MODE_ECB, 0);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to open des cipher (error 0x%x).\n",
                err);
        return err;
    }
    err = ntfs_desx_key_expand(key, (u32*)des_key, &ctx->out_whitening,
            &ctx->in_whitening);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to expand desx key (error 0x%x).\n",
                err);
        gcry_cipher_close(ctx->gcry_cipher_hd);
        return err;
    }
    err = gcry_cipher_setkey(ctx->gcry_cipher_hd, des_key, sizeof(des_key));
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to set des key (error 0x%x).\n", err);
        gcry_cipher_close(ctx->gcry_cipher_hd);
        return err;
    }
    /*
     * Take a note of the ctx->gcry_cipher_hd since we need to close it at
     * ntfs_decrypt_data_key_close() time.
     */
    **(gcry_cipher_hd_t***)(key + ((keylen + 7) & ~7)) =
            &ctx->gcry_cipher_hd;
    return GPG_ERR_NO_ERROR;
}

/**
 * ntfs_desx_decrypt
 */
static void ntfs_desx_decrypt(void *context, u8 *outbuf, const u8 *inbuf)
{
    ntfs_desx_ctx *ctx = context;
    gcry_error_t err;

    err = gcry_cipher_reset(ctx->gcry_cipher_hd);
    if (err != GPG_ERR_NO_ERROR)
        ntfs_log_error("Failed to reset des cipher (error 0x%x).\n",
                err);
    *(u64*)outbuf = *(const u64*)inbuf ^ ctx->out_whitening;
    err = gcry_cipher_encrypt(ctx->gcry_cipher_hd, outbuf, 8, NULL, 0);
    if (err != GPG_ERR_NO_ERROR)
        ntfs_log_error("Des decryption failed (error 0x%x).\n", err);
    *(u64*)outbuf ^= ctx->in_whitening;
}

static gcry_cipher_spec_t ntfs_desx_cipher = {
    .name = "DES-X-MS128",
    .blocksize = 8,
    .keylen = 128,
    .contextsize = sizeof(ntfs_desx_ctx),
    .setkey = ntfs_desx_setkey,
    .decrypt = ntfs_desx_decrypt,
};

#ifdef NTFS_TEST
/*
 * Do not remove this test code from this file!  (AIA)
 * It would be nice to move all tests (these and runlist) out of the library
 * (at least, into the separate file{,s}), so they would not annoy eyes.  (Yura)
 */

/**
 * ntfs_desx_key_expand_test
 */
static BOOL ntfs_desx_key_expand_test(void)
{
    const u8 known_desx_on_disk_key[16] = {
        0xa1, 0xf9, 0xe0, 0xb2, 0x53, 0x23, 0x9e, 0x8f,
        0x0f, 0x91, 0x45, 0xd9, 0x8e, 0x20, 0xec, 0x30
    };
    const u8 known_des_key[8] = {
        0x27, 0xd1, 0x93, 0x09, 0xcb, 0x78, 0x93, 0x1f,
    };
    const u8 known_out_whitening[8] = {
        0xed, 0xda, 0x4c, 0x47, 0x60, 0x49, 0xdb, 0x8d,
    };
    const u8 known_in_whitening[8] = {
        0x75, 0xf6, 0xa0, 0x1a, 0xc0, 0xca, 0x28, 0x1e
    };
    u64 test_out_whitening, test_in_whitening;
    union {
        u64 u64;
        u32 u32[2];
    } test_des_key;
    gcry_error_t err;
    BOOL res;

    err = ntfs_desx_key_expand(known_desx_on_disk_key, test_des_key.u32,
            &test_out_whitening, &test_in_whitening);
    if (err != GPG_ERR_NO_ERROR)
        res = FALSE;
    else
        res = test_des_key.u64 == *(u64*)known_des_key &&
                test_out_whitening ==
                *(u64*)known_out_whitening &&
                test_in_whitening ==
                *(u64*)known_in_whitening;
    ntfs_log_error("Testing whether ntfs_desx_key_expand() works: %s\n",
            res ? "SUCCESS" : "FAILED");
    return res;
}

/**
 * ntfs_des_test
 */
static BOOL ntfs_des_test(void)
{
    const u8 known_des_key[8] = {
        0x27, 0xd1, 0x93, 0x09, 0xcb, 0x78, 0x93, 0x1f
    };
    const u8 known_des_encrypted_data[8] = {
        0xdc, 0xf7, 0x68, 0x2a, 0xaf, 0x48, 0x53, 0x0f
    };
    const u8 known_decrypted_data[8] = {
        0xd8, 0xd9, 0x15, 0x23, 0x5b, 0x88, 0x0e, 0x09
    };
    u8 test_decrypted_data[8];
    int res;
    gcry_error_t err;
    gcry_cipher_hd_t gcry_cipher_hd;

    err = gcry_cipher_open(&gcry_cipher_hd, GCRY_CIPHER_DES,
            GCRY_CIPHER_MODE_ECB, 0);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to open des cipher (error 0x%x).\n",
                err);
        return FALSE;
    }
    err = gcry_cipher_setkey(gcry_cipher_hd, known_des_key,
            sizeof(known_des_key));
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to set des key (error 0x%x.\n", err);
        gcry_cipher_close(gcry_cipher_hd);
        return FALSE;
    }
    /*
     * Apply DES decryption (ntfs actually uses encryption when decrypting).
     */
    err = gcry_cipher_encrypt(gcry_cipher_hd, test_decrypted_data,
            sizeof(test_decrypted_data), known_des_encrypted_data,
            sizeof(known_des_encrypted_data));
    gcry_cipher_close(gcry_cipher_hd);
    if (err) {
        ntfs_log_error("Failed to des decrypt test data (error "
                "0x%x).\n", err);
        return FALSE;
    }
    res = !memcmp(test_decrypted_data, known_decrypted_data,
            sizeof(known_decrypted_data));
    ntfs_log_error("Testing whether des decryption works: %s\n",
            res ? "SUCCESS" : "FAILED");
    return res;
}

#else /* !defined(NTFS_TEST) */

/**
 * ntfs_desx_key_expand_test
 */
static inline BOOL ntfs_desx_key_expand_test(void)
{
    return TRUE;
}

/**
 * ntfs_des_test
 */
static inline BOOL ntfs_des_test(void)
{
    return TRUE;
}

#endif /* !defined(NTFS_TEST) */

/**
 * ntfs_fek_import_from_raw
 */
static ntfs_fek *ntfs_fek_import_from_raw(u8 *fek_buf,
        unsigned fek_size)
{
    ntfs_fek *fek;
    u32 key_size, wanted_key_size, gcry_algo;
    gcry_error_t err;

    key_size = le32_to_cpup(fek_buf);
    ntfs_log_debug("key_size 0x%x\n", key_size);
    if (key_size + 16 > fek_size) {
        ntfs_log_debug("Invalid FEK.  It was probably decrypted with "
                "the incorrect RSA key.");
        errno = EINVAL;
        return NULL;
    }
    fek = malloc(((((sizeof(*fek) + 7) & ~7) + key_size + 7) & ~7) +
            sizeof(gcry_cipher_hd_t));
    if (!fek) {
        errno = ENOMEM;
        return NULL;
    }
    fek->alg_id = *(le32*)(fek_buf + 8);
    ntfs_log_debug("algorithm_id 0x%x\n", le32_to_cpu(fek->alg_id));
    fek->key_data = (u8*)fek + ((sizeof(*fek) + 7) & ~7);
    memcpy(fek->key_data, fek_buf + 16, key_size);
    fek->des_gcry_cipher_hd_ptr = NULL;
    *(gcry_cipher_hd_t***)(fek->key_data + ((key_size + 7) & ~7)) =
            &fek->des_gcry_cipher_hd_ptr;
    switch (fek->alg_id) {
    case CALG_DESX:
        if (!ntfs_crypto_ctx.desx_module) {
            if (!ntfs_desx_key_expand_test() || !ntfs_des_test()) {
                err = EINVAL;
                goto out;
            }
            err = gcry_cipher_register(&ntfs_desx_cipher,
                    &ntfs_crypto_ctx.desx_alg_id,
                    &ntfs_crypto_ctx.desx_module);
            if (err != GPG_ERR_NO_ERROR) {
                ntfs_log_error("Failed to register desx "
                        "cipher: %s\n",
                        gcry_strerror(err));
                err = EINVAL;
                goto out;
            }
        }
        wanted_key_size = 16;
        gcry_algo = ntfs_crypto_ctx.desx_alg_id;
        break;
    case CALG_3DES:
        wanted_key_size = 24;
        gcry_algo = GCRY_CIPHER_3DES;
        break;
    case CALG_AES_256:
        wanted_key_size = 32;
        gcry_algo = GCRY_CIPHER_AES256;
        break;
    default:
        wanted_key_size = 8;
        gcry_algo = GCRY_CIPHER_DES;
        if (fek->alg_id == CALG_DES)
            ntfs_log_error("DES is not supported at present\n");
        else
            ntfs_log_error("Unknown crypto algorithm 0x%x\n",
                    le32_to_cpu(fek->alg_id));
        ntfs_log_error(".  Please email %s and say that you saw this "
                "message.  We will then try to implement "
                "support for this algorithm.\n", NTFS_DEV_LIST);
        err = EOPNOTSUPP;
        goto out;
    }
    if (key_size != wanted_key_size) {
        ntfs_log_error("%s key of %u bytes but needed size is %u "
                "bytes, assuming corrupt or incorrect key.  "
                "Aborting.\n",
                gcry_cipher_algo_name(gcry_algo),
                (unsigned)key_size, (unsigned)wanted_key_size);
        err = EIO;
        goto out;
    }
    err = gcry_cipher_open(&fek->gcry_cipher_hd, gcry_algo,
            GCRY_CIPHER_MODE_CBC, 0);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("gcry_cipher_open() failed: %s\n",
                gcry_strerror(err));
        err = EINVAL;
        goto out;
    }
    err = gcry_cipher_setkey(fek->gcry_cipher_hd, fek->key_data, key_size);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("gcry_cipher_setkey() failed: %s\n",
                gcry_strerror(err));
        gcry_cipher_close(fek->gcry_cipher_hd);
        err = EINVAL;
        goto out;
    }
    return fek;
out:
    free(fek);
    errno = err;
    return NULL;
}

/**
 * ntfs_fek_release
 */
static void ntfs_fek_release(ntfs_fek *fek)
{
    if (fek->des_gcry_cipher_hd_ptr)
        gcry_cipher_close(*fek->des_gcry_cipher_hd_ptr);
    gcry_cipher_close(fek->gcry_cipher_hd);
    free(fek);
}

/**
 * ntfs_df_array_fek_get
 */
static ntfs_fek *ntfs_df_array_fek_get(EFS_DF_ARRAY_HEADER *df_array,
        ntfs_rsa_private_key_t *rsa_key)
{
    EFS_DF_HEADER *df_header;
    EFS_DF_CREDENTIAL_HEADER *df_cred;
    EFS_DF_CERT_THUMBPRINT_HEADER *df_cert;
    u8 *fek_buf;
    ntfs_fek *fek;
    u32 df_count, fek_size;
    unsigned i, thumbprint_size = sizeof(rsa_key->thumbprint);

    df_count = le32_to_cpu(df_array->df_count);
    if (!df_count)
        ntfs_log_error("There are no elements in the DF array.\n");
    df_header = (EFS_DF_HEADER*)(df_array + 1);
    for (i = 0; i < df_count; i++, df_header = (EFS_DF_HEADER*)(
            (u8*)df_header + le32_to_cpu(df_header->df_length))) {
        df_cred = (EFS_DF_CREDENTIAL_HEADER*)((u8*)df_header +
                le32_to_cpu(df_header->cred_header_offset));
        if (df_cred->type != NTFS_CRED_TYPE_CERT_THUMBPRINT) {
            ntfs_log_debug("Credential type is not certificate "
                    "thumbprint, skipping DF entry.\n");
            continue;
        }
        df_cert = (EFS_DF_CERT_THUMBPRINT_HEADER*)((u8*)df_cred +
                le32_to_cpu(
                df_cred->cert_thumbprint_header_offset));
        if (le32_to_cpu(df_cert->thumbprint_size) != thumbprint_size) {
            ntfs_log_error("Thumbprint size %d is not valid "
                    "(should be %d), skipping this DF "
                    "entry.\n",
                    le32_to_cpu(df_cert->thumbprint_size),
                    thumbprint_size);
            continue;
        }
        if (memcmp((u8*)df_cert +
                le32_to_cpu(df_cert->thumbprint_offset),
                rsa_key->thumbprint, thumbprint_size)) {
            ntfs_log_debug("Thumbprints do not match, skipping "
                    "this DF entry.\n");
            continue;
        }
        /*
         * The thumbprints match so this is probably the DF entry
         * matching the RSA key.  Try to decrypt the FEK with it.
         */
        fek_size = le32_to_cpu(df_header->fek_size);
        fek_buf = (u8*)df_header + le32_to_cpu(df_header->fek_offset);
        /* Decrypt the FEK.  Note: This is done in place. */
        fek_size = ntfs_raw_fek_decrypt(fek_buf, fek_size, rsa_key);
        if (fek_size) {
            /* Convert the FEK to our internal format. */
            fek = ntfs_fek_import_from_raw(fek_buf, fek_size);
            if (fek)
                return fek;
            ntfs_log_error("Failed to convert the decrypted file "
                    "encryption key to internal format.\n");
        } else
            ntfs_log_error("Failed to decrypt the file "
                    "encryption key.\n");
    }
    return NULL;
}

/**
 * ntfs_inode_fek_get -
 */
static ntfs_fek *ntfs_inode_fek_get(ntfs_inode *inode,
        ntfs_rsa_private_key_t *rsa_key)
{
    EFS_ATTR_HEADER *efs;
    EFS_DF_ARRAY_HEADER *df_array = NULL;
    ntfs_fek *fek = NULL;

    /* Obtain the $EFS contents. */
    efs = ntfs_attr_readall(inode, AT_LOGGED_UTILITY_STREAM, NTFS_EFS, 4,
            NULL);
    if (!efs) {
        ntfs_log_perror("Failed to read $EFS attribute");
        return NULL;
    }
    /*
     * Depending on whether the key is a normal key or a data recovery key,
     * iterate through the DDF or DRF array, respectively.
     */
    if (rsa_key->df_type == DF_TYPE_DDF) {
        if (efs->offset_to_ddf_array)
            df_array = (EFS_DF_ARRAY_HEADER*)((u8*)efs +
                    le32_to_cpu(efs->offset_to_ddf_array));
        else
            ntfs_log_error("There are no entries in the DDF "
                    "array.\n");
    } else if (rsa_key->df_type == DF_TYPE_DRF) {
        if (efs->offset_to_drf_array)
            df_array = (EFS_DF_ARRAY_HEADER*)((u8*)efs +
                    le32_to_cpu(efs->offset_to_drf_array));
        else
            ntfs_log_error("There are no entries in the DRF "
                    "array.\n");
    } else
        ntfs_log_error("Invalid DF type.\n");
    if (df_array)
        fek = ntfs_df_array_fek_get(df_array, rsa_key);
    free(efs);
    return fek;
}

/**
 * ntfs_fek_decrypt_sector
 */
static int ntfs_fek_decrypt_sector(ntfs_fek *fek, u8 *data, const u64 offset)
{
    gcry_error_t err;

    err = gcry_cipher_reset(fek->gcry_cipher_hd);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to reset cipher: %s\n",
                gcry_strerror(err));
        return -1;
    }
    /*
     * Note: You may wonder why we are not calling gcry_cipher_setiv() here
     * instead of doing it by hand after the decryption.  The answer is
     * that gcry_cipher_setiv() wants an iv of length 8 bytes but we give
     * it a length of 16 for AES256 so it does not like it.
     */
    err = gcry_cipher_decrypt(fek->gcry_cipher_hd, data, 512, NULL, 0);
    if (err != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Decryption failed: %s\n", gcry_strerror(err));
        return -1;
    }
    /* Apply the IV. */
    if (fek->alg_id == CALG_AES_256) {
        ((le64*)data)[0] ^= cpu_to_le64(0x5816657be9161312ULL + offset);
        ((le64*)data)[1] ^= cpu_to_le64(0x1989adbe44918961ULL + offset);
    } else {
        /* All other algorithms (Des, 3Des, DesX) use the same IV. */
        ((le64*)data)[0] ^= cpu_to_le64(0x169119629891ad13ULL + offset);
    }
    return 512;
}

/**
 * ntfs_crypto_deinit - perform library-wide crypto deinitialization
 */
static void ntfs_crypto_deinit(void)
{
    int i;

    if (!ntfs_crypto_ctx.initialized)
        return;

    for (i = 0; i < ntfs_crypto_ctx.nr_rsa_keys; i++)
        ntfs_rsa_private_key_release(ntfs_crypto_ctx.rsa_key[i]);
    free(ntfs_crypto_ctx.rsa_key);
    ntfs_crypto_ctx.rsa_key = NULL;
    ntfs_crypto_ctx.nr_rsa_keys = 0;
    gnutls_global_deinit();
    if (ntfs_crypto_ctx.desx_module) {
        gcry_cipher_unregister(ntfs_crypto_ctx.desx_module);
        ntfs_crypto_ctx.desx_module = NULL;
        ntfs_crypto_ctx.desx_alg_id = -1;
    }
    ntfs_crypto_ctx.initialized = 0;
}


static void ntfs_crypto_parse_config(struct config_t *cfg)
{
    ntfs_crypto_ctx_t *ctx = &ntfs_crypto_ctx;
    config_setting_t *cfg_keys, *cfg_key;
    const char *pfx_file, *pfx_pwd;
    ntfs_rsa_private_key_t *key;
    u8 *pfx_buf;
    unsigned pfx_size;
    int i;

    /* Search for crypto.keys list. */
    cfg_keys = config_lookup(cfg, "crypto.keys");
    if (!cfg_keys) {
        ntfs_log_error("Unable to find crypto.keys in config file.\n");
        return;
    }
    /* Iterate trough list of records about keys. */
    for (i = 0; (cfg_key = config_setting_get_elem(cfg_keys, i)); i++) {
        /* Get path and password to key. */
        pfx_file = config_setting_get_string_elem(cfg_key, 0);
        pfx_pwd = config_setting_get_string_elem(cfg_key, 1);
        if (!pfx_file) {
            ntfs_log_error("Entry number %d in section crypto.keys "
                    "of configuration file formed "
                    "incorrectly.\n", i + 1);
            continue;
        }
        if (!pfx_pwd)
            pfx_pwd = "";
        /* Load the PKCS#12 file containing the user's private key. */
        if (ntfs_pkcs12_load_pfxfile(pfx_file, &pfx_buf, &pfx_size)) {
            ntfs_log_error("Failed to load key file %s.\n",
                    pfx_file);
            continue;
        }
        /*
         * Check whether we need to allocate memory for new key pointer.
         * If yes, allocate memory for it and for 3 more pointers.
         */
        if (!(ctx->nr_rsa_keys % 4)) {
            ntfs_rsa_private_key_t **new;

            new = realloc(ctx->rsa_key,
                    sizeof(ntfs_rsa_private_key_t *) *
                    (ctx->nr_rsa_keys + 4));
            if (!new) {
                ntfs_log_perror("Unable to store all keys");
                break;
            }
            ctx->rsa_key = new;
        }
        /* Obtain the user's private RSA key from the key file. */
        key = ntfs_pkcs12_extract_rsa_key(pfx_buf, pfx_size, pfx_pwd);
        if (key)
            ctx->rsa_key[ctx->nr_rsa_keys++] = key;
        else
            ntfs_log_error("Failed to obtain RSA key from %s\n",
                    pfx_file);
        /* No longer need the pfx file contents. */
        free(pfx_buf);
    }
}


static void ntfs_crypto_read_configs(void)
{
    struct config_t cfg;
    char *home;
    int fd = -1;

    config_init(&cfg);
    /* Load system configuration file. */
    if (config_read_file(&cfg, NTFS_CONFIG_PATH_SYSTEM))
        ntfs_crypto_parse_config(&cfg);
    else
        if (config_error_line(&cfg)) /* Do not cry if file absent. */
            ntfs_log_error("Failed to read system configuration "
                    "file: %s (line %d).\n",
                    config_error_text(&cfg),
                    config_error_line(&cfg));
    /* Load user configuration file. */
    fd = open(".", O_RDONLY); /* Save current working directory. */
    if (fd == -1) {
        ntfs_log_error("Failed to open working directory.\n");
        goto out;
    }
    home = getenv("HOME");
    if (!home) {
        ntfs_log_error("Environment variable HOME is not set.\n");
        goto out;
    }
    if (chdir(home) == -1) {
        ntfs_log_perror("chdir() to home directory failed");
        goto out;
    }
    if (config_read_file(&cfg, NTFS_CONFIG_PATH_USER))
        ntfs_crypto_parse_config(&cfg);
    else
        if (config_error_line(&cfg)) /* Do not cry if file absent. */
            ntfs_log_error("Failed to read user configuration "
                    "file: %s (line %d).\n",
                    config_error_text(&cfg),
                    config_error_line(&cfg));
    if (fchdir(fd) == -1)
        ntfs_log_error("Failed to restore original working "
                "directory.\n");
out:
    if (fd != -1)
        close(fd);
    config_destroy(&cfg);
}

/**
 * ntfs_crypto_init - perform library-wide crypto initializations
 *
 * This function is called during first call of ntfs_crypto_attr_open and
 * performs gcrypt and GNU TLS initializations, then read list of PFX files
 * from configuration files and load RSA keys from them.
 */
static int ntfs_crypto_init(void)
{
    int err;

    if (ntfs_crypto_ctx.initialized)
        return 0;

    /* Initialize gcrypt library.  Note: Must come before GNU TLS init. */
    if (gcry_control(GCRYCTL_DISABLE_SECMEM, 0) != GPG_ERR_NO_ERROR) {
        ntfs_log_error("Failed to initialize the gcrypt library.\n");
        return -1;
    }
    /* Initialize GNU TLS library.  Note: Must come after libgcrypt init. */
    err = gnutls_global_init();
    if (err < 0) {
        ntfs_log_error("Failed to initialize GNU TLS library: %s\n",
                gnutls_strerror(err));
        return -1;
    }
    /* Read crypto related sections of libntfs configuration files. */
    ntfs_crypto_read_configs();

    ntfs_crypto_ctx.initialized = 1;
    atexit(ntfs_crypto_deinit);
    return 0;
}


/**
 * ntfs_crypto_attr_open - perform crypto related initialization for attribute
 * @na:     ntfs attribute to perform initialization for
 *
 * This function is called from ntfs_attr_open for encrypted attributes and
 * tries to decrypt FEK enumerating all user submitted RSA keys. If we
 * successfully obtained FEK, then @na->crypto is allocated and FEK stored
 * inside. In the other case @na->crypto is set to NULL.
 *
 * Return 0 on success and -1 on error with errno set to the error code.
 */
int ntfs_crypto_attr_open(ntfs_attr *na)
{
    ntfs_fek *fek;
    int i;

    na->crypto = NULL;
    if (!na || !NAttrEncrypted(na)) {
        errno = EINVAL;
        return -1;
    }
    if (ntfs_crypto_init()) {
        errno = EACCES;
        return -1;
    }

    for (i = 0; i < ntfs_crypto_ctx.nr_rsa_keys; i++) {
        fek = ntfs_inode_fek_get(na->ni, ntfs_crypto_ctx.rsa_key[i]);
        if (fek) {
            na->crypto = ntfs_malloc(sizeof(ntfs_crypto_attr));
            if (!na->crypto)
                return -1;
            na->crypto->fek = fek;
            return 0;
        }
    }

    errno = EACCES;
    return -1;
}


/**
 * ntfs_crypto_attr_close - perform crypto related deinit for attribute
 * @na:     ntfs attribute to perform deinitialization for
 *
 * This function is called from ntfs_attr_close for encrypted attributes and
 * frees memory that were allocated for it handling.
 */
void ntfs_crypto_attr_close(ntfs_attr *na)
{
    if (!na || !NAttrEncrypted(na))
        return;

    if (na->crypto) {
        ntfs_fek_release(na->crypto->fek);
        free(na->crypto);
    }
}


/**
 * ntfs_crypto_attr_pread - read from an encrypted attribute
 * @na:     ntfs attribute to read from
 * @pos:    byte position in the attribute to begin reading from
 * @count:  number of bytes to read
 * @b:      output data buffer
 *
 * This function is called from ntfs_attr_pread for encrypted attributes and
 * should behave as described in ntfs_attr_pread description.
 */
s64 ntfs_crypto_attr_pread(ntfs_attr *na, const s64 pos, s64 count, void *b)
{
    unsigned char *buffer;
    s64 bytes_read, offset, total, length;
    int i;

    if (!na || pos < 0 || count < 0 || !b || !NAttrEncrypted(na)) {
        errno = EINVAL;
        return -1;
    }
    if (!count)
        return 0;

    if (!na->crypto) {
        errno = EACCES;
        return -1;
    }

    buffer = malloc(NTFS_EFS_SECTOR_SIZE);
    if (!buffer)
        return -1;

    ntfs_attr_map_runlist_range(na, pos >> na->ni->vol->cluster_size_bits,
            (pos + count - 1) >> na->ni->vol->cluster_size_bits);

    total = 0;
    offset = ROUND_DOWN(pos, 9);
    while (total < count && offset < na->data_size) {
        /* Calculate number of bytes we actually want. */
        length = NTFS_EFS_SECTOR_SIZE;
        if (offset + length > pos + count)
            length = pos + count - offset;
        if (offset + length > na->data_size)
            length = na->data_size - offset;

        if (length < 0) {
            total = -1;
            errno = EIO;
            ntfs_log_error("LIBRARY BUG!!! Please report that you "
                    "saw this message to %s. Thanks!",
                    NTFS_DEV_LIST);
            break;
        }

        /* Just write zeros if @offset fully beyond initialized size. */
        if (offset >= na->initialized_size) {
            memset(b + total, 0, length);
            total += length;
            continue;
        }

        bytes_read = ntfs_rl_pread(na->ni->vol, na->rl, offset,
                NTFS_EFS_SECTOR_SIZE, buffer);
        if (!bytes_read)
            break;
        if (bytes_read != NTFS_EFS_SECTOR_SIZE) {
            ntfs_log_perror("%s(): ntfs_rl_pread returned %lld "
                    "bytes", "ntfs_crypto_attr_pread", bytes_read);
            break;
        }
        if ((i = ntfs_fek_decrypt_sector(na->crypto->fek, buffer,
                offset)) < bytes_read) {
            ntfs_log_error("%s(): Couldn't decrypt all data "
                    "(%u/%lld/%lld/%lld)!", "ntfs_crypto_attr_pread",
                    i, (long long)bytes_read,
                    (long long)offset, (long long)total);
            break;
        }

        /* Handle partially in initialized size situation. */
        if (offset + length > na->initialized_size)
            memset(buffer + (na->initialized_size - offset), 0,
                    offset + length - na->initialized_size);

        if (offset >= pos)
            memcpy(b + total, buffer, length);
        else {
            length -= (pos - offset);
            memcpy(b + total, buffer + (pos - offset), length);
        }
        total += length;
        offset += bytes_read;
    }

    free(buffer);
    return total;
}

#else /* !ENABLE_CRYPTO */

/* Stubs for crypto-disabled version of libntfs. */

int ntfs_crypto_attr_open(ntfs_attr *na)
{
    na->crypto = NULL;
    errno = EACCES;
    return -1;
}

void ntfs_crypto_attr_close(ntfs_attr *na)
{
}

s64 ntfs_crypto_attr_pread(ntfs_attr *na, const s64 pos, s64 count,
        void *b)
{
    errno = EACCES;
    return -1;
}

#endif /* !ENABLE_CRYPTO */