authfile.c

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/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains functions for reading and writing identity files, and
 * for reading the passphrase from the user.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 *
 * Copyright (c) 2000 Markus Friedl.  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 ``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 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.
 */

#include "includes.h"
RCSID("$OpenBSD: authfile.c,v 1.61 2005/06/17 02:44:32 djm Exp $");

#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/pem.h>

#include "cipher.h"
#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "key.h"
#include "ssh.h"
#include "log.h"
#include "authfile.h"
#include "rsa.h"
#include "misc.h"
#include "atomicio.h"

/* Version identification string for SSH v1 identity files. */
static const char authfile_id_string[] =
    "SSH PRIVATE KEY FILE FORMAT 1.1\n";

/*
 * Saves the authentication (private) key in a file, encrypting it with
 * passphrase.  The identification of the file (lowest 64 bits of n) will
 * precede the key to provide identification of the key without needing a
 * passphrase.
 */

static int
key_save_private_rsa1(Key *key, const char *filename, const char *passphrase,
    const char *comment)
{
        Buffer buffer, encrypted;
        u_char buf[100], *cp;
        int fd, i, cipher_num;
        CipherContext ciphercontext;
        Cipher *cipher;
        u_int32_t rnd;

        /*
         * If the passphrase is empty, use SSH_CIPHER_NONE to ease converting
         * to another cipher; otherwise use SSH_AUTHFILE_CIPHER.
         */
        cipher_num = (strcmp(passphrase, "") == 0) ?
            SSH_CIPHER_NONE : SSH_AUTHFILE_CIPHER;
        if ((cipher = cipher_by_number(cipher_num)) == NULL)
                fatal("save_private_key_rsa: bad cipher");

        /* This buffer is used to built the secret part of the private key. */
        buffer_init(&buffer);

        /* Put checkbytes for checking passphrase validity. */
        rnd = arc4random();
        buf[0] = rnd & 0xff;
        buf[1] = (rnd >> 8) & 0xff;
        buf[2] = buf[0];
        buf[3] = buf[1];
        buffer_append(&buffer, buf, 4);

        /*
         * Store the private key (n and e will not be stored because they
         * will be stored in plain text, and storing them also in encrypted
         * format would just give known plaintext).
         */
        buffer_put_bignum(&buffer, key->rsa->d);
        buffer_put_bignum(&buffer, key->rsa->iqmp);
        buffer_put_bignum(&buffer, key->rsa->q);        /* reverse from SSL p */
        buffer_put_bignum(&buffer, key->rsa->p);        /* reverse from SSL q */

        /* Pad the part to be encrypted until its size is a multiple of 8. */
        while (buffer_len(&buffer) % 8 != 0)
                buffer_put_char(&buffer, 0);

        /* This buffer will be used to contain the data in the file. */
        buffer_init(&encrypted);

        /* First store keyfile id string. */
        for (i = 0; authfile_id_string[i]; i++)
                buffer_put_char(&encrypted, authfile_id_string[i]);
        buffer_put_char(&encrypted, 0);

        /* Store cipher type. */
        buffer_put_char(&encrypted, cipher_num);
        buffer_put_int(&encrypted, 0);  /* For future extension */

        /* Store public key.  This will be in plain text. */
        buffer_put_int(&encrypted, BN_num_bits(key->rsa->n));
        buffer_put_bignum(&encrypted, key->rsa->n);
        buffer_put_bignum(&encrypted, key->rsa->e);
        buffer_put_cstring(&encrypted, comment);

        /* Allocate space for the private part of the key in the buffer. */
        cp = buffer_append_space(&encrypted, buffer_len(&buffer));

        cipher_set_key_string(&ciphercontext, cipher, passphrase,
            CIPHER_ENCRYPT);
        cipher_crypt(&ciphercontext, cp,
            buffer_ptr(&buffer), buffer_len(&buffer));
        cipher_cleanup(&ciphercontext);
        memset(&ciphercontext, 0, sizeof(ciphercontext));

        /* Destroy temporary data. */
        memset(buf, 0, sizeof(buf));
        buffer_free(&buffer);

        fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
        if (fd < 0) {
                error("open %s failed: %s.", filename, strerror(errno));
                buffer_free(&encrypted);
                return 0;
        }
        if (atomicio(vwrite, fd, buffer_ptr(&encrypted),
            buffer_len(&encrypted)) != buffer_len(&encrypted)) {
                error("write to key file %s failed: %s", filename,
                    strerror(errno));
                buffer_free(&encrypted);
                close(fd);
                unlink(filename);
                return 0;
        }
        close(fd);
        buffer_free(&encrypted);
        return 1;
}

/* save SSH v2 key in OpenSSL PEM format */
static int
key_save_private_pem(Key *key, const char *filename, const char *_passphrase,
    const char *comment)
{
        FILE *fp;
        int fd;
        int success = 0;
        int len = strlen(_passphrase);
        u_char *passphrase = (len > 0) ? (u_char *)_passphrase : NULL;
        const EVP_CIPHER *cipher = (len > 0) ? EVP_des_ede3_cbc() : NULL;

        if (len > 0 && len <= 4) {
                error("passphrase too short: have %d bytes, need > 4", len);
                return 0;
        }
        fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
        if (fd < 0) {
                error("open %s failed: %s.", filename, strerror(errno));
                return 0;
        }
        fp = fdopen(fd, "w");
        if (fp == NULL ) {
                error("fdopen %s failed: %s.", filename, strerror(errno));
                close(fd);
                return 0;
        }
        switch (key->type) {
        case KEY_DSA:
                success = PEM_write_DSAPrivateKey(fp, key->dsa,
                    cipher, passphrase, len, NULL, NULL);
                break;
        case KEY_RSA:
                success = PEM_write_RSAPrivateKey(fp, key->rsa,
                    cipher, passphrase, len, NULL, NULL);
                break;
        }
        fclose(fp);
        return success;
}

int
key_save_private(Key *key, const char *filename, const char *passphrase,
    const char *comment)
{
        switch (key->type) {
        case KEY_RSA1:
                return key_save_private_rsa1(key, filename, passphrase,
                    comment);
                break;
        case KEY_DSA:
        case KEY_RSA:
                return key_save_private_pem(key, filename, passphrase,
                    comment);
                break;
        default:
                break;
        }
        error("key_save_private: cannot save key type %d", key->type);
        return 0;
}

/*
 * Loads the public part of the ssh v1 key file.  Returns NULL if an error was
 * encountered (the file does not exist or is not readable), and the key
 * otherwise.
 */

static Key *
key_load_public_rsa1(int fd, const char *filename, char **commentp)
{
        Buffer buffer;
        Key *pub;
        struct stat st;
        char *cp;
        u_int i;
        size_t len;

        if (fstat(fd, &st) < 0) {
                error("fstat for key file %.200s failed: %.100s",
                    filename, strerror(errno));
                return NULL;
        }
        if (st.st_size > 1*1024*1024) {
                error("key file %.200s too large", filename);
                return NULL;
        }
        len = (size_t)st.st_size;               /* truncated */

        buffer_init(&buffer);
        cp = buffer_append_space(&buffer, len);

        if (atomicio(read, fd, cp, len) != len) {
                debug("Read from key file %.200s failed: %.100s", filename,
                    strerror(errno));
                buffer_free(&buffer);
                return NULL;
        }

        /* Check that it is at least big enough to contain the ID string. */
        if (len < sizeof(authfile_id_string)) {
                debug3("Not a RSA1 key file %.200s.", filename);
                buffer_free(&buffer);
                return NULL;
        }
        /*
         * Make sure it begins with the id string.  Consume the id string
         * from the buffer.
         */
        for (i = 0; i < sizeof(authfile_id_string); i++)
                if (buffer_get_char(&buffer) != authfile_id_string[i]) {
                        debug3("Not a RSA1 key file %.200s.", filename);
                        buffer_free(&buffer);
                        return NULL;
                }
        /* Skip cipher type and reserved data. */
        (void) buffer_get_char(&buffer);        /* cipher type */
        (void) buffer_get_int(&buffer);         /* reserved */

        /* Read the public key from the buffer. */
        (void) buffer_get_int(&buffer);
        pub = key_new(KEY_RSA1);
        buffer_get_bignum(&buffer, pub->rsa->n);
        buffer_get_bignum(&buffer, pub->rsa->e);
        if (commentp)
                *commentp = buffer_get_string(&buffer, NULL);
        /* The encrypted private part is not parsed by this function. */

        buffer_free(&buffer);
        return pub;
}

/* load public key from private-key file, works only for SSH v1 */
Key *
key_load_public_type(int type, const char *filename, char **commentp)
{
        Key *pub;
        int fd;

        if (type == KEY_RSA1) {
                fd = open(filename, O_RDONLY);
                if (fd < 0)
                        return NULL;
                pub = key_load_public_rsa1(fd, filename, commentp);
                close(fd);
                return pub;
        }
        return NULL;
}

/*
 * Loads the private key from the file.  Returns 0 if an error is encountered
 * (file does not exist or is not readable, or passphrase is bad). This
 * initializes the private key.
 * Assumes we are called under uid of the owner of the file.
 */

static Key *
key_load_private_rsa1(int fd, const char *filename, const char *passphrase,
    char **commentp)
{
        u_int i;
        int check1, check2, cipher_type;
        size_t len;
        Buffer buffer, decrypted;
        u_char *cp;
        CipherContext ciphercontext;
        Cipher *cipher;
        Key *prv = NULL;
        struct stat st;

        if (fstat(fd, &st) < 0) {
                error("fstat for key file %.200s failed: %.100s",
                    filename, strerror(errno));
                close(fd);
                return NULL;
        }
        if (st.st_size > 1*1024*1024) {
                error("key file %.200s too large", filename);
                close(fd);
                return (NULL);
        }
        len = (size_t)st.st_size;               /* truncated */

        buffer_init(&buffer);
        cp = buffer_append_space(&buffer, len);

        if (atomicio(read, fd, cp, len) != len) {
                debug("Read from key file %.200s failed: %.100s", filename,
                    strerror(errno));
                buffer_free(&buffer);
                close(fd);
                return NULL;
        }

        /* Check that it is at least big enough to contain the ID string. */
        if (len < sizeof(authfile_id_string)) {
                debug3("Not a RSA1 key file %.200s.", filename);
                buffer_free(&buffer);
                close(fd);
                return NULL;
        }
        /*
         * Make sure it begins with the id string.  Consume the id string
         * from the buffer.
         */
        for (i = 0; i < sizeof(authfile_id_string); i++)
                if (buffer_get_char(&buffer) != authfile_id_string[i]) {
                        debug3("Not a RSA1 key file %.200s.", filename);
                        buffer_free(&buffer);
                        close(fd);
                        return NULL;
                }

        /* Read cipher type. */
        cipher_type = buffer_get_char(&buffer);
        (void) buffer_get_int(&buffer); /* Reserved data. */

        /* Read the public key from the buffer. */
        (void) buffer_get_int(&buffer);
        prv = key_new_private(KEY_RSA1);

        buffer_get_bignum(&buffer, prv->rsa->n);
        buffer_get_bignum(&buffer, prv->rsa->e);
        if (commentp)
                *commentp = buffer_get_string(&buffer, NULL);
        else
                xfree(buffer_get_string(&buffer, NULL));

        /* Check that it is a supported cipher. */
        cipher = cipher_by_number(cipher_type);
        if (cipher == NULL) {
                debug("Unsupported cipher %d used in key file %.200s.",
                    cipher_type, filename);
                buffer_free(&buffer);
                goto fail;
        }
        /* Initialize space for decrypted data. */
        buffer_init(&decrypted);
        cp = buffer_append_space(&decrypted, buffer_len(&buffer));

        /* Rest of the buffer is encrypted.  Decrypt it using the passphrase. */
        cipher_set_key_string(&ciphercontext, cipher, passphrase,
            CIPHER_DECRYPT);
        cipher_crypt(&ciphercontext, cp,
            buffer_ptr(&buffer), buffer_len(&buffer));
        cipher_cleanup(&ciphercontext);
        memset(&ciphercontext, 0, sizeof(ciphercontext));
        buffer_free(&buffer);

        check1 = buffer_get_char(&decrypted);
        check2 = buffer_get_char(&decrypted);
        if (check1 != buffer_get_char(&decrypted) ||
            check2 != buffer_get_char(&decrypted)) {
                if (strcmp(passphrase, "") != 0)
                        debug("Bad passphrase supplied for key file %.200s.",
                            filename);
                /* Bad passphrase. */
                buffer_free(&decrypted);
                goto fail;
        }
        /* Read the rest of the private key. */
        buffer_get_bignum(&decrypted, prv->rsa->d);
        buffer_get_bignum(&decrypted, prv->rsa->iqmp);          /* u */
        /* in SSL and SSH v1 p and q are exchanged */
        buffer_get_bignum(&decrypted, prv->rsa->q);             /* p */
        buffer_get_bignum(&decrypted, prv->rsa->p);             /* q */

        /* calculate p-1 and q-1 */
        rsa_generate_additional_parameters(prv->rsa);

        buffer_free(&decrypted);

        /* enable blinding */
        if (RSA_blinding_on(prv->rsa, NULL) != 1) {
                error("key_load_private_rsa1: RSA_blinding_on failed");
                goto fail;
        }
        close(fd);
        return prv;

fail:
        if (commentp)
                xfree(*commentp);
        close(fd);
        key_free(prv);
        return NULL;
}

Key *
key_load_private_pem(int fd, int type, const char *passphrase,
    char **commentp)
{
        FILE *fp;
        EVP_PKEY *pk = NULL;
        Key *prv = NULL;
        char *name = "<no key>";

        fp = fdopen(fd, "r");
        if (fp == NULL) {
                error("fdopen failed: %s", strerror(errno));
                close(fd);
                return NULL;
        }
        pk = PEM_read_PrivateKey(fp, NULL, NULL, (char *)passphrase);
        if (pk == NULL) {
                debug("PEM_read_PrivateKey failed");
                (void)ERR_get_error();
        } else if (pk->type == EVP_PKEY_RSA &&
            (type == KEY_UNSPEC||type==KEY_RSA)) {
                prv = key_new(KEY_UNSPEC);
                prv->rsa = EVP_PKEY_get1_RSA(pk);
                prv->type = KEY_RSA;
                name = "rsa w/o comment";
#ifdef DEBUG_PK
                RSA_print_fp(stderr, prv->rsa, 8);
#endif
                if (RSA_blinding_on(prv->rsa, NULL) != 1) {
                        error("key_load_private_pem: RSA_blinding_on failed");
                        key_free(prv);
                        prv = NULL;
                }
        } else if (pk->type == EVP_PKEY_DSA &&
            (type == KEY_UNSPEC||type==KEY_DSA)) {
                prv = key_new(KEY_UNSPEC);
                prv->dsa = EVP_PKEY_get1_DSA(pk);
                prv->type = KEY_DSA;
                name = "dsa w/o comment";
#ifdef DEBUG_PK
                DSA_print_fp(stderr, prv->dsa, 8);
#endif
        } else {
                error("PEM_read_PrivateKey: mismatch or "
                    "unknown EVP_PKEY save_type %d", pk->save_type);
        }
        fclose(fp);
        if (pk != NULL)
                EVP_PKEY_free(pk);
        if (prv != NULL && commentp)
                *commentp = xstrdup(name);
        debug("read PEM private key done: type %s",
            prv ? key_type(prv) : "<unknown>");
        return prv;
}

static int
key_perm_ok(int fd, const char *filename)
{
        struct stat st;

        if (fstat(fd, &st) < 0)
                return 0;
        /*
         * if a key owned by the user is accessed, then we check the
         * permissions of the file. if the key owned by a different user,
         * then we don't care.
         */
#ifdef HAVE_CYGWIN
        if (check_ntsec(filename))
#endif
        if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0) {
                error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                error("@         WARNING: UNPROTECTED PRIVATE KEY FILE!          @");
                error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
                error("Permissions 0%3.3o for '%s' are too open.",
                    (u_int)st.st_mode & 0777, filename);
                error("It is recommended that your private key files are NOT accessible by others.");
                error("This private key will be ignored.");
                return 0;
        }
        return 1;
}

Key *
key_load_private_type(int type, const char *filename, const char *passphrase,
    char **commentp)
{
        int fd;

        fd = open(filename, O_RDONLY);
        if (fd < 0)
                return NULL;
        if (!key_perm_ok(fd, filename)) {
                error("bad permissions: ignore key: %s", filename);
                close(fd);
                return NULL;
        }
        switch (type) {
        case KEY_RSA1:
                return key_load_private_rsa1(fd, filename, passphrase,
                    commentp);
                /* closes fd */
                break;
        case KEY_DSA:
        case KEY_RSA:
        case KEY_UNSPEC:
                return key_load_private_pem(fd, type, passphrase, commentp);
                /* closes fd */
                break;
        default:
                close(fd);
                break;
        }
        return NULL;
}

Key *
key_load_private(const char *filename, const char *passphrase,
    char **commentp)
{
        Key *pub, *prv;
        int fd;

        fd = open(filename, O_RDONLY);
        if (fd < 0)
                return NULL;
        if (!key_perm_ok(fd, filename)) {
                error("bad permissions: ignore key: %s", filename);
                close(fd);
                return NULL;
        }
        pub = key_load_public_rsa1(fd, filename, commentp);
        lseek(fd, (off_t) 0, SEEK_SET);         /* rewind */
        if (pub == NULL) {
                /* closes fd */
                prv = key_load_private_pem(fd, KEY_UNSPEC, passphrase, NULL);
                /* use the filename as a comment for PEM */
                if (commentp && prv)
                        *commentp = xstrdup(filename);
        } else {
                /* it's a SSH v1 key if the public key part is readable */
                key_free(pub);
                /* closes fd */
                prv = key_load_private_rsa1(fd, filename, passphrase, NULL);
        }
        return prv;
}

static int
key_try_load_public(Key *k, const char *filename, char **commentp)
{
        FILE *f;
        char line[SSH_MAX_PUBKEY_BYTES];
        char *cp;
        u_long linenum = 0;

        f = fopen(filename, "r");
        if (f != NULL) {
                while (read_keyfile_line(f, filename, line, sizeof(line),
                            &linenum) != -1) {
                        cp = line;
                        switch (*cp) {
                        case '#':
                        case '\n':
                        case '\0':
                                continue;
                        }
                        /* Skip leading whitespace. */
                        for (; *cp && (*cp == ' ' || *cp == '\t'); cp++)
                                ;
                        if (*cp) {
                                if (key_read(k, &cp) == 1) {
                                        if (commentp)
                                                *commentp=xstrdup(filename);
                                        fclose(f);
                                        return 1;
                                }
                        }
                }
                fclose(f);
        }
        return 0;
}

/* load public key from ssh v1 private or any pubkey file */
Key *
key_load_public(const char *filename, char **commentp)
{
        Key *pub;
        char file[MAXPATHLEN];

        /* try rsa1 private key */
        pub = key_load_public_type(KEY_RSA1, filename, commentp);
        if (pub != NULL)
                return pub;

        /* try rsa1 public key */
        pub = key_new(KEY_RSA1);
        if (key_try_load_public(pub, filename, commentp) == 1)
                return pub;
        key_free(pub);

        /* try ssh2 public key */
        pub = key_new(KEY_UNSPEC);
        if (key_try_load_public(pub, filename, commentp) == 1)
                return pub;
        if ((strlcpy(file, filename, sizeof file) < sizeof(file)) &&
            (strlcat(file, ".pub", sizeof file) < sizeof(file)) &&
            (key_try_load_public(pub, file, commentp) == 1))
                return pub;
        key_free(pub);
        return NULL;
}

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