Refactor crypto.[ch] into smaller DH module.

Add two new files (crypto_dh.c, crypto_dh.h) as new module of crypto.[ch]. This
new module includes all functions and dependencies related to DH operations.
Those have been removed from crypto.[ch].

Follows #24658.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>

1 files changed, 2 insertions, 578 deletions

diff --git a/src/common/crypto.c b/src/common/crypto.c
index 6518ea9cc6..072fed792e 100644
--- a/src/common/crypto.c
+++ b/src/common/crypto.c
@@ -27,6 +27,7 @@
 #include "crypto.h"
 #include "crypto_curve25519.h"
 #include "crypto_digest.h"
+#include "crypto_dh.h"
 #include "crypto_ed25519.h"
 #include "crypto_format.h"
 #include "crypto_rand.h"
@@ -72,14 +73,6 @@ ENABLE_GCC_WARNING(redundant-decls)
 
 #include "keccak-tiny/keccak-tiny.h"
 
-/** A structure to hold the first half (x, g^x) of a Diffie-Hellman handshake
- * while we're waiting for the second.*/
-struct crypto_dh_t {
-  DH *dh; /**< The openssl DH object */
-};
-
-static int tor_check_dh_key(int severity, const BIGNUM *bn);
-
 /** Boolean: has OpenSSL's crypto been initialized? */
 static int crypto_early_initialized_ = 0;
 
@@ -285,14 +278,6 @@ crypto_thread_cleanup(void)
 #endif
 }
 
-/** Used by tortls.c: Get the DH* from a crypto_dh_t.
- */
-DH *
-crypto_dh_get_dh_(crypto_dh_t *dh)
-{
-  return dh->dh;
-}
-
 /** Allocate and return a new symmetric cipher using the provided key and iv.
  * The key is <b>bits</b> bits long; the IV is CIPHER_IV_LEN bytes.  Both
  * must be provided. Key length must be 128, 192, or 256 */
@@ -480,560 +465,6 @@ crypto_cipher_decrypt_with_iv(const char *key,
   return (int)(fromlen - CIPHER_IV_LEN);
 }
 
-/* DH */
-
-/** Our DH 'g' parameter */
-#define DH_GENERATOR 2
-
-/** Shared P parameter for our circuit-crypto DH key exchanges. */
-static BIGNUM *dh_param_p = NULL;
-/** Shared P parameter for our TLS DH key exchanges. */
-static BIGNUM *dh_param_p_tls = NULL;
-/** Shared G parameter for our DH key exchanges. */
-static BIGNUM *dh_param_g = NULL;
-
-/** Validate a given set of Diffie-Hellman parameters.  This is moderately
- * computationally expensive (milliseconds), so should only be called when
- * the DH parameters change. Returns 0 on success, * -1 on failure.
- */
-static int
-crypto_validate_dh_params(const BIGNUM *p, const BIGNUM *g)
-{
-  DH *dh = NULL;
-  int ret = -1;
-
-  /* Copy into a temporary DH object, just so that DH_check() can be called. */
-  if (!(dh = DH_new()))
-      goto out;
-#ifdef OPENSSL_1_1_API
-  BIGNUM *dh_p, *dh_g;
-  if (!(dh_p = BN_dup(p)))
-    goto out;
-  if (!(dh_g = BN_dup(g)))
-    goto out;
-  if (!DH_set0_pqg(dh, dh_p, NULL, dh_g))
-    goto out;
-#else /* !(defined(OPENSSL_1_1_API)) */
-  if (!(dh->p = BN_dup(p)))
-    goto out;
-  if (!(dh->g = BN_dup(g)))
-    goto out;
-#endif /* defined(OPENSSL_1_1_API) */
-
-  /* Perform the validation. */
-  int codes = 0;
-  if (!DH_check(dh, &codes))
-    goto out;
-  if (BN_is_word(g, DH_GENERATOR_2)) {
-    /* Per https://wiki.openssl.org/index.php/Diffie-Hellman_parameters
-     *
-     * OpenSSL checks the prime is congruent to 11 when g = 2; while the
-     * IETF's primes are congruent to 23 when g = 2.
-     */
-    BN_ULONG residue = BN_mod_word(p, 24);
-    if (residue == 11 || residue == 23)
-      codes &= ~DH_NOT_SUITABLE_GENERATOR;
-  }
-  if (codes != 0) /* Specifics on why the params suck is irrelevant. */
-    goto out;
-
-  /* Things are probably not evil. */
-  ret = 0;
-
- out:
-  if (dh)
-    DH_free(dh);
-  return ret;
-}
-
-/** Set the global Diffie-Hellman generator, used for both TLS and internal
- * DH stuff.
- */
-static void
-crypto_set_dh_generator(void)
-{
-  BIGNUM *generator;
-  int r;
-
-  if (dh_param_g)
-    return;
-
-  generator = BN_new();
-  tor_assert(generator);
-
-  r = BN_set_word(generator, DH_GENERATOR);
-  tor_assert(r);
-
-  dh_param_g = generator;
-}
-
-/** Set the global TLS Diffie-Hellman modulus.  Use the Apache mod_ssl DH
- * modulus. */
-void
-crypto_set_tls_dh_prime(void)
-{
-  BIGNUM *tls_prime = NULL;
-  int r;
-
-  /* If the space is occupied, free the previous TLS DH prime */
-  if (BUG(dh_param_p_tls)) {
-    /* LCOV_EXCL_START
-     *
-     * We shouldn't be calling this twice.
-     */
-    BN_clear_free(dh_param_p_tls);
-    dh_param_p_tls = NULL;
-    /* LCOV_EXCL_STOP */
-  }
-
-  tls_prime = BN_new();
-  tor_assert(tls_prime);
-
-  /* This is the 1024-bit safe prime that Apache uses for its DH stuff; see
-   * modules/ssl/ssl_engine_dh.c; Apache also uses a generator of 2 with this
-   * prime.
-   */
-  r = BN_hex2bn(&tls_prime,
-               "D67DE440CBBBDC1936D693D34AFD0AD50C84D239A45F520BB88174CB98"
-               "BCE951849F912E639C72FB13B4B4D7177E16D55AC179BA420B2A29FE324A"
-               "467A635E81FF5901377BEDDCFD33168A461AAD3B72DAE8860078045B07A7"
-               "DBCA7874087D1510EA9FCC9DDD330507DD62DB88AEAA747DE0F4D6E2BD68"
-               "B0E7393E0F24218EB3");
-  tor_assert(r);
-
-  tor_assert(tls_prime);
-
-  dh_param_p_tls = tls_prime;
-  crypto_set_dh_generator();
-  tor_assert(0 == crypto_validate_dh_params(dh_param_p_tls, dh_param_g));
-}
-
-/** Initialize dh_param_p and dh_param_g if they are not already
- * set. */
-static void
-init_dh_param(void)
-{
-  BIGNUM *circuit_dh_prime;
-  int r;
-  if (BUG(dh_param_p && dh_param_g))
-    return; // LCOV_EXCL_LINE This function isn't supposed to be called twice.
-
-  circuit_dh_prime = BN_new();
-  tor_assert(circuit_dh_prime);
-
-  /* This is from rfc2409, section 6.2.  It's a safe prime, and
-     supposedly it equals:
-        2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
-  */
-  r = BN_hex2bn(&circuit_dh_prime,
-                "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E08"
-                "8A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B"
-                "302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9"
-                "A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE6"
-                "49286651ECE65381FFFFFFFFFFFFFFFF");
-  tor_assert(r);
-
-  /* Set the new values as the global DH parameters. */
-  dh_param_p = circuit_dh_prime;
-  crypto_set_dh_generator();
-  tor_assert(0 == crypto_validate_dh_params(dh_param_p, dh_param_g));
-
-  if (!dh_param_p_tls) {
-    crypto_set_tls_dh_prime();
-  }
-}
-
-/** Number of bits to use when choosing the x or y value in a Diffie-Hellman
- * handshake.  Since we exponentiate by this value, choosing a smaller one
- * lets our handhake go faster.
- */
-#define DH_PRIVATE_KEY_BITS 320
-
-/** Allocate and return a new DH object for a key exchange. Returns NULL on
- * failure.
- */
-crypto_dh_t *
-crypto_dh_new(int dh_type)
-{
-  crypto_dh_t *res = tor_malloc_zero(sizeof(crypto_dh_t));
-
-  tor_assert(dh_type == DH_TYPE_CIRCUIT || dh_type == DH_TYPE_TLS ||
-             dh_type == DH_TYPE_REND);
-
-  if (!dh_param_p)
-    init_dh_param();
-
-  if (!(res->dh = DH_new()))
-    goto err;
-
-#ifdef OPENSSL_1_1_API
-  BIGNUM *dh_p = NULL, *dh_g = NULL;
-
-  if (dh_type == DH_TYPE_TLS) {
-    dh_p = BN_dup(dh_param_p_tls);
-  } else {
-    dh_p = BN_dup(dh_param_p);
-  }
-  if (!dh_p)
-    goto err;
-
-  dh_g = BN_dup(dh_param_g);
-  if (!dh_g) {
-    BN_free(dh_p);
-    goto err;
-  }
-
-  if (!DH_set0_pqg(res->dh, dh_p, NULL, dh_g)) {
-    goto err;
-  }
-
-  if (!DH_set_length(res->dh, DH_PRIVATE_KEY_BITS))
-    goto err;
-#else /* !(defined(OPENSSL_1_1_API)) */
-  if (dh_type == DH_TYPE_TLS) {
-    if (!(res->dh->p = BN_dup(dh_param_p_tls)))
-      goto err;
-  } else {
-    if (!(res->dh->p = BN_dup(dh_param_p)))
-      goto err;
-  }
-
-  if (!(res->dh->g = BN_dup(dh_param_g)))
-    goto err;
-
-  res->dh->length = DH_PRIVATE_KEY_BITS;
-#endif /* defined(OPENSSL_1_1_API) */
-
-  return res;
-
-  /* LCOV_EXCL_START
-   * This error condition is only reached when an allocation fails */
- err:
-  crypto_log_errors(LOG_WARN, "creating DH object");
-  if (res->dh) DH_free(res->dh); /* frees p and g too */
-  tor_free(res);
-  return NULL;
-  /* LCOV_EXCL_STOP */
-}
-
-/** Return a copy of <b>dh</b>, sharing its internal state. */
-crypto_dh_t *
-crypto_dh_dup(const crypto_dh_t *dh)
-{
-  crypto_dh_t *dh_new = tor_malloc_zero(sizeof(crypto_dh_t));
-  tor_assert(dh);
-  tor_assert(dh->dh);
-  dh_new->dh = dh->dh;
-  DH_up_ref(dh->dh);
-  return dh_new;
-}
-
-/** Return the length of the DH key in <b>dh</b>, in bytes.
- */
-int
-crypto_dh_get_bytes(crypto_dh_t *dh)
-{
-  tor_assert(dh);
-  return DH_size(dh->dh);
-}
-
-/** Generate \<x,g^x\> for our part of the key exchange.  Return 0 on
- * success, -1 on failure.
- */
-int
-crypto_dh_generate_public(crypto_dh_t *dh)
-{
-#ifndef OPENSSL_1_1_API
- again:
-#endif
-  if (!DH_generate_key(dh->dh)) {
-    /* LCOV_EXCL_START
-     * To test this we would need some way to tell openssl to break DH. */
-    crypto_log_errors(LOG_WARN, "generating DH key");
-    return -1;
-    /* LCOV_EXCL_STOP */
-  }
-#ifdef OPENSSL_1_1_API
-  /* OpenSSL 1.1.x doesn't appear to let you regenerate a DH key, without
-   * recreating the DH object.  I have no idea what sort of aliasing madness
-   * can occur here, so do the check, and just bail on failure.
-   */
-  const BIGNUM *pub_key, *priv_key;
-  DH_get0_key(dh->dh, &pub_key, &priv_key);
-  if (tor_check_dh_key(LOG_WARN, pub_key)<0) {
-    log_warn(LD_CRYPTO, "Weird! Our own DH key was invalid.  I guess once-in-"
-             "the-universe chances really do happen.  Treating as a failure.");
-    return -1;
-  }
-#else /* !(defined(OPENSSL_1_1_API)) */
-  if (tor_check_dh_key(LOG_WARN, dh->dh->pub_key)<0) {
-    /* LCOV_EXCL_START
-     * If this happens, then openssl's DH implementation is busted. */
-    log_warn(LD_CRYPTO, "Weird! Our own DH key was invalid.  I guess once-in-"
-             "the-universe chances really do happen.  Trying again.");
-    /* Free and clear the keys, so OpenSSL will actually try again. */
-    BN_clear_free(dh->dh->pub_key);
-    BN_clear_free(dh->dh->priv_key);
-    dh->dh->pub_key = dh->dh->priv_key = NULL;
-    goto again;
-    /* LCOV_EXCL_STOP */
-  }
-#endif /* defined(OPENSSL_1_1_API) */
-  return 0;
-}
-
-/** Generate g^x as necessary, and write the g^x for the key exchange
- * as a <b>pubkey_len</b>-byte value into <b>pubkey</b>. Return 0 on
- * success, -1 on failure.  <b>pubkey_len</b> must be \>= DH_BYTES.
- */
-int
-crypto_dh_get_public(crypto_dh_t *dh, char *pubkey, size_t pubkey_len)
-{
-  int bytes;
-  tor_assert(dh);
-
-  const BIGNUM *dh_pub;
-
-#ifdef OPENSSL_1_1_API
-  const BIGNUM *dh_priv;
-  DH_get0_key(dh->dh, &dh_pub, &dh_priv);
-#else
-  dh_pub = dh->dh->pub_key;
-#endif /* defined(OPENSSL_1_1_API) */
-
-  if (!dh_pub) {
-    if (crypto_dh_generate_public(dh)<0)
-      return -1;
-    else {
-#ifdef OPENSSL_1_1_API
-      DH_get0_key(dh->dh, &dh_pub, &dh_priv);
-#else
-      dh_pub = dh->dh->pub_key;
-#endif
-    }
-  }
-
-  tor_assert(dh_pub);
-  bytes = BN_num_bytes(dh_pub);
-  tor_assert(bytes >= 0);
-  if (pubkey_len < (size_t)bytes) {
-    log_warn(LD_CRYPTO,
-             "Weird! pubkey_len (%d) was smaller than DH_BYTES (%d)",
-             (int) pubkey_len, bytes);
-    return -1;
-  }
-
-  memset(pubkey, 0, pubkey_len);
-  BN_bn2bin(dh_pub, (unsigned char*)(pubkey+(pubkey_len-bytes)));
-
-  return 0;
-}
-
-/** Check for bad Diffie-Hellman public keys (g^x).  Return 0 if the key is
- * okay (in the subgroup [2,p-2]), or -1 if it's bad.
- * See http://www.cl.cam.ac.uk/ftp/users/rja14/psandqs.ps.gz for some tips.
- */
-static int
-tor_check_dh_key(int severity, const BIGNUM *bn)
-{
-  BIGNUM *x;
-  char *s;
-  tor_assert(bn);
-  x = BN_new();
-  tor_assert(x);
-  if (BUG(!dh_param_p))
-    init_dh_param(); //LCOV_EXCL_LINE we already checked whether we did this.
-  BN_set_word(x, 1);
-  if (BN_cmp(bn,x)<=0) {
-    log_fn(severity, LD_CRYPTO, "DH key must be at least 2.");
-    goto err;
-  }
-  BN_copy(x,dh_param_p);
-  BN_sub_word(x, 1);
-  if (BN_cmp(bn,x)>=0) {
-    log_fn(severity, LD_CRYPTO, "DH key must be at most p-2.");
-    goto err;
-  }
-  BN_clear_free(x);
-  return 0;
- err:
-  BN_clear_free(x);
-  s = BN_bn2hex(bn);
-  log_fn(severity, LD_CRYPTO, "Rejecting insecure DH key [%s]", s);
-  OPENSSL_free(s);
-  return -1;
-}
-
-/** Given a DH key exchange object, and our peer's value of g^y (as a
- * <b>pubkey_len</b>-byte value in <b>pubkey</b>) generate
- * <b>secret_bytes_out</b> bytes of shared key material and write them
- * to <b>secret_out</b>.  Return the number of bytes generated on success,
- * or -1 on failure.
- *
- * (We generate key material by computing
- *         SHA1( g^xy || "\x00" ) || SHA1( g^xy || "\x01" ) || ...
- * where || is concatenation.)
- */
-ssize_t
-crypto_dh_compute_secret(int severity, crypto_dh_t *dh,
-                         const char *pubkey, size_t pubkey_len,
-                         char *secret_out, size_t secret_bytes_out)
-{
-  char *secret_tmp = NULL;
-  BIGNUM *pubkey_bn = NULL;
-  size_t secret_len=0, secret_tmp_len=0;
-  int result=0;
-  tor_assert(dh);
-  tor_assert(secret_bytes_out/DIGEST_LEN <= 255);
-  tor_assert(pubkey_len < INT_MAX);
-
-  if (!(pubkey_bn = BN_bin2bn((const unsigned char*)pubkey,
-                              (int)pubkey_len, NULL)))
-    goto error;
-  if (tor_check_dh_key(severity, pubkey_bn)<0) {
-    /* Check for invalid public keys. */
-    log_fn(severity, LD_CRYPTO,"Rejected invalid g^x");
-    goto error;
-  }
-  secret_tmp_len = crypto_dh_get_bytes(dh);
-  secret_tmp = tor_malloc(secret_tmp_len);
-  result = DH_compute_key((unsigned char*)secret_tmp, pubkey_bn, dh->dh);
-  if (result < 0) {
-    log_warn(LD_CRYPTO,"DH_compute_key() failed.");
-    goto error;
-  }
-  secret_len = result;
-  if (crypto_expand_key_material_TAP((uint8_t*)secret_tmp, secret_len,
-                                     (uint8_t*)secret_out, secret_bytes_out)<0)
-    goto error;
-  secret_len = secret_bytes_out;
-
-  goto done;
- error:
-  result = -1;
- done:
-  crypto_log_errors(LOG_WARN, "completing DH handshake");
-  if (pubkey_bn)
-    BN_clear_free(pubkey_bn);
-  if (secret_tmp) {
-    memwipe(secret_tmp, 0, secret_tmp_len);
-    tor_free(secret_tmp);
-  }
-  if (result < 0)
-    return result;
-  else
-    return secret_len;
-}
-
-/** Given <b>key_in_len</b> bytes of negotiated randomness in <b>key_in</b>
- * ("K"), expand it into <b>key_out_len</b> bytes of negotiated key material in
- * <b>key_out</b> by taking the first <b>key_out_len</b> bytes of
- *    H(K | [00]) | H(K | [01]) | ....
- *
- * This is the key expansion algorithm used in the "TAP" circuit extension
- * mechanism; it shouldn't be used for new protocols.
- *
- * Return 0 on success, -1 on failure.
- */
-int
-crypto_expand_key_material_TAP(const uint8_t *key_in, size_t key_in_len,
-                               uint8_t *key_out, size_t key_out_len)
-{
-  int i, r = -1;
-  uint8_t *cp, *tmp = tor_malloc(key_in_len+1);
-  uint8_t digest[DIGEST_LEN];
-
-  /* If we try to get more than this amount of key data, we'll repeat blocks.*/
-  tor_assert(key_out_len <= DIGEST_LEN*256);
-
-  memcpy(tmp, key_in, key_in_len);
-  for (cp = key_out, i=0; cp < key_out+key_out_len;
-       ++i, cp += DIGEST_LEN) {
-    tmp[key_in_len] = i;
-    if (crypto_digest((char*)digest, (const char *)tmp, key_in_len+1) < 0)
-      goto exit;
-    memcpy(cp, digest, MIN(DIGEST_LEN, key_out_len-(cp-key_out)));
-  }
-
-  r = 0;
- exit:
-  memwipe(tmp, 0, key_in_len+1);
-  tor_free(tmp);
-  memwipe(digest, 0, sizeof(digest));
-  return r;
-}
-
-/** Expand some secret key material according to RFC5869, using SHA256 as the
- * underlying hash.  The <b>key_in_len</b> bytes at <b>key_in</b> are the
- * secret key material; the <b>salt_in_len</b> bytes at <b>salt_in</b> and the
- * <b>info_in_len</b> bytes in <b>info_in_len</b> are the algorithm's "salt"
- * and "info" parameters respectively.  On success, write <b>key_out_len</b>
- * bytes to <b>key_out</b> and return 0.  Assert on failure.
- */
-int
-crypto_expand_key_material_rfc5869_sha256(
-                                    const uint8_t *key_in, size_t key_in_len,
-                                    const uint8_t *salt_in, size_t salt_in_len,
-                                    const uint8_t *info_in, size_t info_in_len,
-                                    uint8_t *key_out, size_t key_out_len)
-{
-  uint8_t prk[DIGEST256_LEN];
-  uint8_t tmp[DIGEST256_LEN + 128 + 1];
-  uint8_t mac[DIGEST256_LEN];
-  int i;
-  uint8_t *outp;
-  size_t tmp_len;
-
-  crypto_hmac_sha256((char*)prk,
-                     (const char*)salt_in, salt_in_len,
-                     (const char*)key_in, key_in_len);
-
-  /* If we try to get more than this amount of key data, we'll repeat blocks.*/
-  tor_assert(key_out_len <= DIGEST256_LEN * 256);
-  tor_assert(info_in_len <= 128);
-  memset(tmp, 0, sizeof(tmp));
-  outp = key_out;
-  i = 1;
-
-  while (key_out_len) {
-    size_t n;
-    if (i > 1) {
-      memcpy(tmp, mac, DIGEST256_LEN);
-      memcpy(tmp+DIGEST256_LEN, info_in, info_in_len);
-      tmp[DIGEST256_LEN+info_in_len] = i;
-      tmp_len = DIGEST256_LEN + info_in_len + 1;
-    } else {
-      memcpy(tmp, info_in, info_in_len);
-      tmp[info_in_len] = i;
-      tmp_len = info_in_len + 1;
-    }
-    crypto_hmac_sha256((char*)mac,
-                       (const char*)prk, DIGEST256_LEN,
-                       (const char*)tmp, tmp_len);
-    n = key_out_len < DIGEST256_LEN ? key_out_len : DIGEST256_LEN;
-    memcpy(outp, mac, n);
-    key_out_len -= n;
-    outp += n;
-    ++i;
-  }
-
-  memwipe(tmp, 0, sizeof(tmp));
-  memwipe(mac, 0, sizeof(mac));
-  return 0;
-}
-
-/** Free a DH key exchange object.
- */
-void
-crypto_dh_free_(crypto_dh_t *dh)
-{
-  if (!dh)
-    return;
-  tor_assert(dh->dh);
-  DH_free(dh->dh);
-  tor_free(dh);
-}
-
 /** @{ */
 /** Uninitialize the crypto library. Return 0 on success. Does not detect
  * failure.
@@ -1051,14 +482,7 @@ crypto_global_cleanup(void)
   ERR_free_strings();
 #endif
 
-  if (dh_param_p)
-    BN_clear_free(dh_param_p);
-  if (dh_param_p_tls)
-    BN_clear_free(dh_param_p_tls);
-  if (dh_param_g)
-    BN_clear_free(dh_param_g);
-
-  dh_param_p = dh_param_p_tls = dh_param_g = NULL;
+  crypto_dh_free_all();
 
 #ifndef DISABLE_ENGINES
 #if OPENSSL_VERSION_NUMBER < OPENSSL_V_SERIES(1,1,0)