[paraslash.git] / crypt.c

/*
 * Copyright (C) 2005-2011 Andre Noll <maan@systemlinux.org>
 *
 * Licensed under the GPL v2. For licencing details see COPYING.
 */

/** \file crypt.c Openssl-based encryption/decryption routines. */

#include <regex.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <openssl/rand.h>
#include <openssl/err.h>
#include <openssl/rc4.h>
#include <openssl/pem.h>
#include <openssl/sha.h>
#include <openssl/bn.h>

#include "para.h"
#include "error.h"
#include "string.h"
#include "crypt.h"
#include "fd.h"

struct asymmetric_key {
        RSA *rsa;
};

/**
 * Fill a buffer with random content.
 *
 * \param buf The buffer to fill.
 * \param num The size of \a buf in bytes.
 *
 * This function puts \a num cryptographically strong pseudo-random bytes into
 * buf. If libssl can not guarantee an unpredictable byte sequence (for example
 * because the PRNG has not been seeded with enough randomness) the function
 * logs an error message and calls exit().
 */
void get_random_bytes_or_die(unsigned char *buf, int num)
{
        unsigned long err;

        /* RAND_bytes() returns 1 on success, 0 otherwise. */
        if (RAND_bytes(buf, num) == 1)
                return;
        err = ERR_get_error();
        PARA_EMERG_LOG("%s\n", ERR_reason_error_string(err));
        exit(EXIT_FAILURE);
}

/**
 * Seed pseudo random number generators.
 *
 * This function reads 64 bytes from /dev/urandom and adds them to the SSL
 * PRNG. It also seeds the PRNG used by random() with a random seed obtained
 * from SSL. If /dev/random could not be read, an error message is logged and
 * the function calls exit().
 *
 * \sa RAND_load_file(3), \ref get_random_bytes_or_die(), srandom(3),
 * random(3), \ref para_random().
 */
void init_random_seed_or_die(void)
{
        int seed, ret = RAND_load_file("/dev/urandom", 64);

        if (ret != 64) {
                PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
                exit(EXIT_FAILURE);
        }
        get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
        srandom(seed);
}

static int check_key_file(const char *file, int private)
{
        struct stat st;

        if (stat(file, &st) != 0)
                return -ERRNO_TO_PARA_ERROR(errno);
        if (private != LOAD_PRIVATE_KEY)
                return 0;
        if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
                return -E_KEY_PERM;
        return 1;
}

static EVP_PKEY *load_key(const char *file, int private)
{
        BIO *key;
        EVP_PKEY *pkey = NULL;
        int ret = check_key_file(file, private);

        if (ret < 0) {
                PARA_ERROR_LOG("%s\n", para_strerror(-ret));
                return NULL;
        }
        key = BIO_new(BIO_s_file());
        if (!key)
                return NULL;
        if (BIO_read_filename(key, file) > 0) {
                if (private == LOAD_PRIVATE_KEY)
                        pkey = PEM_read_bio_PrivateKey(key, NULL, NULL, NULL);
                else
                        pkey = PEM_read_bio_PUBKEY(key, NULL, NULL, NULL);
        }
        BIO_free(key);
        return pkey;
}

static int get_openssl_key(const char *key_file, RSA **rsa, int private)
{
        EVP_PKEY *key = load_key(key_file, private);

        if (!key)
                return (private == LOAD_PRIVATE_KEY)? -E_PRIVATE_KEY
                        : -E_PUBLIC_KEY;
        *rsa = EVP_PKEY_get1_RSA(key);
        EVP_PKEY_free(key);
        if (!*rsa)
                return -E_RSA;
        return RSA_size(*rsa);
}

#define KEY_TYPE_TXT "ssh-rsa"

/* check if it is an ssh rsa key */
static size_t is_ssh_rsa_key(char *data, size_t size)
{
        char *cp;

        if (size < strlen(KEY_TYPE_TXT) + 2)
                return 0;
        cp = memchr(data, ' ', size);
        if (cp == NULL)
                return 0;
        if (strncmp(KEY_TYPE_TXT, data, strlen(KEY_TYPE_TXT)))
                return 0;
        cp++;
        if (cp >= data + size)
                return 0;
        if (*cp == '\0')
                return 0;
        return cp - data;
}

/*
 * This base64/uudecode stuff below is taken from openssh-5.2p1, Copyright (c)
 * 1996 by Internet Software Consortium.  Portions Copyright (c) 1995 by
 * International Business Machines, Inc.
 */

static const char Base64[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char Pad64 = '=';
/*
 * Skips all whitespace anywhere. Converts characters, four at a time, starting
 * at (or after) src from base - 64 numbers into three 8 bit bytes in the
 * target area. it returns the number of data bytes stored at the target, or -1
 * on error.
 */
static int base64_decode(char const *src, unsigned char *target, size_t targsize)
{
        unsigned int tarindex, state;
        int ch;
        char *pos;

        state = 0;
        tarindex = 0;

        while ((ch = *src++) != '\0') {
                if (para_isspace(ch)) /* Skip whitespace anywhere. */
                        continue;

                if (ch == Pad64)
                        break;

                pos = strchr(Base64, ch);
                if (pos == 0) /* A non-base64 character. */
                        return -1;

                switch (state) {
                case 0:
                        if (target) {
                                if (tarindex >= targsize)
                                        return (-1);
                                target[tarindex] = (pos - Base64) << 2;
                        }
                        state = 1;
                        break;
                case 1:
                        if (target) {
                                if (tarindex + 1 >= targsize)
                                        return (-1);
                                target[tarindex]   |=  (pos - Base64) >> 4;
                                target[tarindex+1]  = ((pos - Base64) & 0x0f)
                                                        << 4 ;
                        }
                        tarindex++;
                        state = 2;
                        break;
                case 2:
                        if (target) {
                                if (tarindex + 1 >= targsize)
                                        return (-1);
                                target[tarindex]   |=  (pos - Base64) >> 2;
                                target[tarindex+1]  = ((pos - Base64) & 0x03)
                                                        << 6;
                        }
                        tarindex++;
                        state = 3;
                        break;
                case 3:
                        if (target) {
                                if (tarindex >= targsize)
                                        return (-1);
                                target[tarindex] |= (pos - Base64);
                        }
                        tarindex++;
                        state = 0;
                        break;
                }
        }

        /*
         * We are done decoding Base-64 chars.  Let's see if we ended
         * on a byte boundary, and/or with erroneous trailing characters.
         */

        if (ch == Pad64) {              /* We got a pad char. */
                ch = *src++;            /* Skip it, get next. */
                switch (state) {
                case 0:         /* Invalid = in first position */
                case 1:         /* Invalid = in second position */
                        return (-1);

                case 2:         /* Valid, means one byte of info */
                        /* Skip any number of spaces. */
                        for (; ch != '\0'; ch = *src++)
                                if (!isspace(ch))
                                        break;
                        /* Make sure there is another trailing = sign. */
                        if (ch != Pad64)
                                return (-1);
                        ch = *src++;            /* Skip the = */
                        /* Fall through to "single trailing =" case. */
                        /* FALLTHROUGH */

                case 3:         /* Valid, means two bytes of info */
                        /*
                         * We know this char is an =.  Is there anything but
                         * whitespace after it?
                         */
                        for (; ch != '\0'; ch = *src++)
                                if (!isspace(ch))
                                        return (-1);

                        /*
                         * Now make sure for cases 2 and 3 that the "extra"
                         * bits that slopped past the last full byte were
                         * zeros.  If we don't check them, they become a
                         * subliminal channel.
                         */
                        if (target && target[tarindex] != 0)
                                return (-1);
                }
        } else {
                /*
                 * We ended by seeing the end of the string.  Make sure we
                 * have no partial bytes lying around.
                 */
                if (state != 0)
                        return (-1);
        }

        return (tarindex);
}

static int uudecode(const char *src, unsigned char *target, size_t targsize)
{
        int len;
        char *encoded, *p;

        /* copy the 'readonly' source */
        encoded = para_strdup(src);
        /* skip whitespace and data */
        for (p = encoded; *p == ' ' || *p == '\t'; p++)
                ;
        for (; *p != '\0' && *p != ' ' && *p != '\t'; p++)
                ;
        /* and remove trailing whitespace because base64_decode needs this */
        *p = '\0';
        len = base64_decode(encoded, target, targsize);
        free(encoded);
        return len >= 0? len : -E_BASE64;
}

/*
 * The public key loading functions below were inspired by corresponding code
 * of openssh-5.2p1, Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo,
 * Finland. However, not much of the original code remains.
 */


/*
 * Can not use the inline functions of portable_io.h here because the byte
 * order is different.
 */
static uint32_t read_ssh_u32(const void *vp)
{
        const unsigned char *p = (const unsigned char *)vp;
        uint32_t v;

        v  = (uint32_t)p[0] << 24;
        v |= (uint32_t)p[1] << 16;
        v |= (uint32_t)p[2] << 8;
        v |= (uint32_t)p[3];

        return v;
}

static int read_bignum(const unsigned char *buf, size_t len, BIGNUM **result)
{
        const unsigned char *p = buf, *end = buf + len;
        uint32_t bnsize;
        BIGNUM *bn;

        if (p + 4 < p)
                return -E_BIGNUM;
        if (p + 4 > end)
                return -E_BIGNUM;
        bnsize = read_ssh_u32(p);
        PARA_DEBUG_LOG("bnsize: %u\n", bnsize);
        p += 4;
        if (p + bnsize < p)
                return -E_BIGNUM;
        if (p + bnsize > end)
                return -E_BIGNUM;
        if (bnsize > 8192)
                return -E_BIGNUM;
        bn = BN_bin2bn(p, bnsize, NULL);
        if (!bn)
                return -E_BIGNUM;
        *result = bn;
        return bnsize + 4;
}

static int read_rsa_bignums(const unsigned char *blob, int blen, RSA **result)
{
        int ret;
        RSA *rsa;
        const unsigned char *p = blob, *end = blob + blen;
        uint32_t rlen;

        *result = NULL;
        if (p + 4 > end)
                return -E_BIGNUM;
        rlen = read_ssh_u32(p);
        p += 4;
        if (p + rlen < p)
                return -E_BIGNUM;
        if (p + rlen > end)
                return -E_BIGNUM;
        if (rlen < strlen(KEY_TYPE_TXT))
                return -E_BIGNUM;
        PARA_DEBUG_LOG("type: %s, rlen: %d\n", p, rlen);
        if (strncmp((char *)p, KEY_TYPE_TXT, strlen(KEY_TYPE_TXT)))
                return -E_BIGNUM;
        p += rlen;

        rsa = RSA_new();
        if (!rsa)
                return -E_BIGNUM;
        ret = read_bignum(p, end - p, &rsa->e);
        if (ret < 0)
                goto fail;
        p += ret;
        ret = read_bignum(p, end - p, &rsa->n);
        if (ret < 0)
                goto fail;
        *result = rsa;
        return 1;
fail:
        if (rsa)
                RSA_free(rsa);
        return ret;
}

/**
 * Read an asymmetric key from a file.
 *
 * \param key_file The file containing the key.
 * \param private if non-zero, read the private key, otherwise the public key.
 * \param result The key structure is returned here.
 *
 * \return The size of the key on success, negative on errors.
 *
 * \sa openssl(1), rsa(1).
 */
int get_asymmetric_key(const char *key_file, int private,
                struct asymmetric_key **result)
{
        struct asymmetric_key *key = NULL;
        void *map = NULL;
        unsigned char *blob = NULL;
        size_t map_size, blob_size;
        int ret, ret2;
        char *cp;

        key = para_malloc(sizeof(*key));
        if (private) {
                ret = get_openssl_key(key_file, &key->rsa, LOAD_PRIVATE_KEY);
                goto out;
        }
        ret = mmap_full_file(key_file, O_RDONLY, &map, &map_size, NULL);
        if (ret < 0)
                goto out;
        ret = is_ssh_rsa_key(map, map_size);
        if (!ret) {
                ret = para_munmap(map, map_size);
                map = NULL;
                if (ret < 0)
                        goto out;
                ret = get_openssl_key(key_file, &key->rsa, LOAD_PUBLIC_KEY);
                goto out;
        }
        cp = map + ret;
        PARA_INFO_LOG("decoding public rsa-ssh key %s\n", key_file);
        ret = -ERRNO_TO_PARA_ERROR(EOVERFLOW);
        if (map_size > INT_MAX / 4)
                goto out;
        blob_size = 2 * map_size;
        blob = para_malloc(blob_size);
        ret = uudecode(cp, blob, blob_size);
        if (ret < 0)
                goto out;
        ret = read_rsa_bignums(blob, ret, &key->rsa);
        if (ret < 0)
                goto out;
        ret = RSA_size(key->rsa);
out:
        ret2 = para_munmap(map, map_size);
        if (ret >= 0 && ret2 < 0)
                ret = ret2;
        if (ret < 0) {
                free(key);
                result = NULL;
                PARA_ERROR_LOG("key %s: %s\n", key_file, para_strerror(-ret));
        } else
                *result = key;
        free(blob);
        return ret;
}

/**
 * Deallocate an asymmetric key structure.
 *
 * \param key Pointer to the key structure to free.
 *
 * This must be called for any key obtained by get_asymmetric_key().
 */
void free_asymmetric_key(struct asymmetric_key *key)
{
        if (!key)
                return;
        RSA_free(key->rsa);
        free(key);
}

/**
 * Decrypt a buffer using a private key.
 *
 * \param key_file Full path of the key.
 * \param outbuf The output buffer.
 * \param inbuf The encrypted input buffer.
 * \param inlen The length of \a inbuf in bytes.
 *
 * The \a outbuf must be large enough to hold at least \a rsa_inlen bytes.
 *
 * \return The size of the recovered plaintext on success, negative on errors.
 *
 * \sa RSA_private_decrypt(3)
 **/
int priv_decrypt(const char *key_file, unsigned char *outbuf,
                unsigned char *inbuf, int inlen)
{
        struct asymmetric_key *priv;
        int ret;

        if (inlen < 0)
                return -E_RSA;
        ret = get_asymmetric_key(key_file, LOAD_PRIVATE_KEY, &priv);
        if (ret < 0)
                return ret;
        /*
         * RSA is vulnerable to timing attacks. Generate a random blinding
         * factor to protect against this kind of attack.
         */
        ret = -E_BLINDING;
        if (RSA_blinding_on(priv->rsa, NULL) == 0)
                goto out;
        ret = RSA_private_decrypt(inlen, inbuf, outbuf, priv->rsa,
                RSA_PKCS1_OAEP_PADDING);
        RSA_blinding_off(priv->rsa);
        if (ret <= 0)
                ret = -E_DECRYPT;
out:
        free_asymmetric_key(priv);
        return ret;
}

/**
 * Encrypt a buffer using an RSA key
 *
 * \param pub: The public key.
 * \param inbuf The input buffer.
 * \param len The length of \a inbuf.
 * \param outbuf The output buffer.
 *
 * \return The size of the encrypted data on success, negative on errors.
 *
 * \sa RSA_public_encrypt(3)
 */
int pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
                unsigned len, unsigned char *outbuf)
{
        int ret, flen = len; /* RSA_public_encrypt expects a signed int */

        if (flen < 0)
                return -E_ENCRYPT;
        ret = RSA_public_encrypt(flen, inbuf, outbuf, pub->rsa,
                RSA_PKCS1_OAEP_PADDING);
        return ret < 0? -E_ENCRYPT : ret;
}

struct stream_cipher {
        RC4_KEY key;
};

/**
 * Allocate and initialize a stream cipher structure.
 *
 * \param data The key.
 * \param len The size of the key.
 *
 * \return A new stream cipher structure.
 */
struct stream_cipher *sc_new(const unsigned char *data, int len)
{
        struct stream_cipher *sc = para_malloc(sizeof(*sc));
        RC4_set_key(&sc->key, len, data);
        return sc;
}

/**
 * Deallocate a stream cipher structure.
 *
 * \param sc A stream cipher previously obtained by sc_new().
 */
void sc_free(struct stream_cipher *sc)
{
        free(sc);
}

/**
 * The RC4() implementation of openssl apparently reads and writes data in
 * blocks of 8 bytes. So we have to make sure our buffer sizes are a multiple
 * of this.
 */
#define RC4_ALIGN 8

/**
 * Encrypt and send a buffer.
 *
 * \param scc The context.
 * \param buf The buffer to send.
 * \param len The size of \a buf in bytes.
 *
 * \return The return value of the underyling call to write_all().
 *
 * \sa \ref write_all(), RC4(3).
 */
int sc_send_bin_buffer(struct stream_cipher_context *scc, const char *buf,
                size_t len)
{
        int ret;
        unsigned char *tmp;
        static unsigned char remainder[RC4_ALIGN];
        size_t l1 = ROUND_DOWN(len, RC4_ALIGN), l2 = ROUND_UP(len, RC4_ALIGN);

        assert(len);
        tmp = para_malloc(l2);
        RC4(&scc->send->key, l1, (const unsigned char *)buf, tmp);
        if (len > l1) {
                memcpy(remainder, buf + l1, len - l1);
                RC4(&scc->send->key, len - l1, remainder, tmp + l1);
        }
        ret = write_all(scc->fd, (char *)tmp, &len);
        free(tmp);
        return ret;
}

/**
 * Encrypt and send a \p NULL-terminated buffer.
 *
 * \param scc The context.
 * \param buf The buffer to send.
 *
 * \return The return value of the underyling call to sc_send_bin_buffer().
 */
int sc_send_buffer(struct stream_cipher_context *scc, const char *buf)
{
        return sc_send_bin_buffer(scc, buf, strlen(buf));
}

/**
 * Format, encrypt and send a buffer.
 *
 * \param scc The context.
 * \param fmt A format string.
 *
 * \return The return value of the underyling call to sc_send_buffer().
 */
__printf_2_3 int sc_send_va_buffer(struct stream_cipher_context *scc,
                const char *fmt, ...)
{
        char *msg;
        int ret;

        PARA_VSPRINTF(fmt, msg);
        ret = sc_send_buffer(scc, msg);
        free(msg);
        return ret;
}

/**
 * Receive a buffer and decrypt it.
 *
 * \param scc The context.
 * \param buf The buffer to write the decrypted data to.
 * \param size The size of \a buf.
 *
 * \return The number of bytes received on success, negative on errors, zero if
 * the peer has performed an orderly shutdown.
 *
 * \sa recv(2), RC4(3).
 */
int sc_recv_bin_buffer(struct stream_cipher_context *scc, char *buf,
                size_t size)
{
        unsigned char *tmp = para_malloc(size);
        ssize_t ret = recv(scc->fd, tmp, size, 0);

        if (ret > 0)
                RC4(&scc->recv->key, ret, tmp, (unsigned char *)buf);
        else if (ret < 0)
                ret = -ERRNO_TO_PARA_ERROR(errno);
        free(tmp);
        return ret;
}

/**
 * Receive a buffer, decrypt it and write terminating NULL byte.
 *
 * \param scc The context.
 * \param buf The buffer to write the decrypted data to.
 * \param size The size of \a buf.
 *
 * Read at most \a size - 1 bytes from file descriptor given by \a scc, decrypt
 * the received data and write a NULL byte at the end of the decrypted data.
 *
 * \return The return value of the underlying call to \ref
 * sc_recv_bin_buffer().
 */
int sc_recv_buffer(struct stream_cipher_context *scc, char *buf, size_t size)
{
        int n;

        assert(size);
        n = sc_recv_bin_buffer(scc, buf, size - 1);
        if (n >= 0)
                buf[n] = '\0';
        else
                *buf = '\0';
        return n;
}

/**
 * Compute the hash of the given input data.
 *
 * \param data Pointer to the data to compute the hash value from.
 * \param len The length of \a data in bytes.
 * \param hash Result pointer.
 *
 * \a hash must point to an area at least \p HASH_SIZE bytes large.
 *
 * \sa sha(3), openssl(1).
 * */
void hash_function(const char *data, unsigned long len, unsigned char *hash)
{
        SHA_CTX c;
        SHA1_Init(&c);
        SHA1_Update(&c, data, len);
        SHA1_Final(hash, &c);
}