tor/src/common/crypto.c

/* Copyright 2001,2002 Roger Dingledine, Matej Pfajfar. */
/* See LICENSE for licensing information */
/* $Id$ */

#include <string.h>

#include <openssl/err.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/opensslv.h>
#include <openssl/bn.h>
#include <openssl/dh.h>

#include <stdlib.h>
#include <assert.h>
#include <stdio.h>

#include "crypto.h"
#include "../or/or.h"
#include "log.h"
#include "aes.h"

#if OPENSSL_VERSION_NUMBER < 0x00905000l
#error "We require openssl >= 0.9.5"
#elif OPENSSL_VERSION_NUMBER < 0x00906000l
#define OPENSSL_095
#endif

/*
 * Certain functions that return a success code in OpenSSL 0.9.6 return void
 * (and don't indicate errors) in OpenSSL version 0.9.5.
 *
 * [OpenSSL 0.9.5 matters, because it ships with Redhat 6.2.]
 */
#ifdef OPENSSL_095
#define RETURN_SSL_OUTCOME(exp) (exp); return 0
#else
#define RETURN_SSL_OUTCOME(exp) return !(exp)
#endif

struct crypto_pk_env_t
{
  int type;
  int refs; /* reference counting; so we don't have to copy keys */
  unsigned char *key;
  /* auxiliary data structure(s) used by the underlying crypto library */
  unsigned char *aux;
};

struct crypto_cipher_env_t
{
  int type;
  unsigned char *key;
  unsigned char *iv;
  /* auxiliary data structure(s) used by the underlying crypto library */
  unsigned char *aux;
};

/* static INLINE const EVP_CIPHER *
   crypto_cipher_evp_cipher(int type, int enc);
*/

static INLINE int 
crypto_cipher_iv_length(int type) {
  /*
  printf("%d -> %d IV\n",type, EVP_CIPHER_iv_length(
						  crypto_cipher_evp_cipher(type,0)));
  */
  switch(type) 
    {
    case CRYPTO_CIPHER_IDENTITY: return 0;
    case CRYPTO_CIPHER_DES: return 8;
    case CRYPTO_CIPHER_RC4: return 16;
    case CRYPTO_CIPHER_3DES: return 8;
    case CRYPTO_CIPHER_AES_CTR: return 0;
    default: assert(0); return -1;
    }
}

static INLINE int
crypto_cipher_key_length(int type) {
  /*
  printf("%d -> %d\n",type, EVP_CIPHER_key_length(
						  crypto_cipher_evp_cipher(type,0)));
  */
  switch(type) 
    {
    case CRYPTO_CIPHER_IDENTITY: return 0;
    case CRYPTO_CIPHER_DES: return 8;
    case CRYPTO_CIPHER_RC4: return 16;
    case CRYPTO_CIPHER_3DES: return 16;
    case CRYPTO_CIPHER_AES_CTR: return 16;
    default: assert(0); return -1;
    }
}

static INLINE const EVP_CIPHER *
crypto_cipher_evp_cipher(int type, int enc) {
  switch(type) 
    {
    case CRYPTO_CIPHER_IDENTITY: return EVP_enc_null();
    case CRYPTO_CIPHER_DES: return EVP_des_ofb();
    case CRYPTO_CIPHER_RC4: return EVP_rc4();
    case CRYPTO_CIPHER_3DES: return EVP_des_ede_ofb();
    default: return NULL;
    }
}

int crypto_global_init() 
{
  ERR_load_crypto_strings();
  return 0;
}

int crypto_global_cleanup()
{
  ERR_free_strings();
  return 0;
}

crypto_pk_env_t *_crypto_new_pk_env_rsa(RSA *rsa)
{
  crypto_pk_env_t *env;
  assert(rsa);
  env = (crypto_pk_env_t *)tor_malloc(sizeof(crypto_pk_env_t));
  env->type = CRYPTO_PK_RSA;
  env->refs = 1;
  env->key = (unsigned char*)rsa;
  env->aux = NULL;
  return env;
}

RSA *_crypto_pk_env_get_rsa(crypto_pk_env_t *env)
{
  if (env->type != CRYPTO_PK_RSA)
    return NULL;
  return (RSA*)env->key;
}

EVP_PKEY *_crypto_pk_env_get_evp_pkey(crypto_pk_env_t *env)
{
  RSA *key = NULL;
  EVP_PKEY *pkey = NULL;
  if (env->type != CRYPTO_PK_RSA)
    return NULL;
  assert(env->key);
  if (!(key = RSAPrivateKey_dup((RSA*)env->key)))
    goto error;
  if (!(pkey = EVP_PKEY_new()))
    goto error;
  if (!(EVP_PKEY_assign_RSA(pkey, key)))
    goto error;
  return pkey;
 error:
  if (pkey)
    EVP_PKEY_free(pkey);
  if (key)
    RSA_free(key);
  return NULL;
}

crypto_pk_env_t *crypto_new_pk_env(int type)
{
  RSA *rsa;

  switch(type) {
    case CRYPTO_PK_RSA:
      rsa = RSA_new();
      if (!rsa) return NULL;
      return _crypto_new_pk_env_rsa(rsa);
    default:
      return NULL;
  }
}

void crypto_free_pk_env(crypto_pk_env_t *env)
{
  assert(env);

  if(--env->refs > 0)
    return;
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
      if (env->key)
        RSA_free((RSA *)env->key);
      break;
    default:
      break;
  }
  
  free(env);
}


/* Create a new crypto_cipher_env_t for a given onion cipher type, key,
 * iv, and encryption flag (1=encrypt, 0=decrypt).  Return the crypto object
 * on success; NULL on failure.
 */
crypto_cipher_env_t *
crypto_create_init_cipher(int cipher_type, char *key, char *iv, int encrypt_mode) 
{
  int r;
  crypto_cipher_env_t *crypto = NULL;

  if (! (crypto = crypto_new_cipher_env(cipher_type))) {
    log_fn(LOG_ERR, "Unable to allocate crypto object");
    return NULL;
  }

  if (crypto_cipher_set_key(crypto, key)) {
    log_fn(LOG_ERR, "Unable to set key: %s", crypto_perror());
    goto error;
  }

  if (crypto_cipher_set_iv(crypto, iv)) {
    log_fn(LOG_ERR, "Unable to set iv: %s", crypto_perror());
    goto error;
  }
  
  if (encrypt_mode)
    r = crypto_cipher_encrypt_init_cipher(crypto);
  else
    r = crypto_cipher_decrypt_init_cipher(crypto);

  if (r) {
    log_fn(LOG_ERR, "Unable to initialize cipher: %s", crypto_perror());
    goto error;
  }
  return crypto;

 error:
  if (crypto)
    crypto_free_cipher_env(crypto);
  return NULL;
}

crypto_cipher_env_t *crypto_new_cipher_env(int type)
{
  crypto_cipher_env_t *env;
  int iv_len, key_len;
  
  env = (crypto_cipher_env_t *)tor_malloc(sizeof(crypto_cipher_env_t));
  
  env->type = type;
  env->key = NULL;
  env->iv = NULL;
  env->aux = NULL;

  iv_len = crypto_cipher_iv_length(type);
  key_len = crypto_cipher_key_length(type);
  
  if (type == CRYPTO_CIPHER_AES_CTR) {
    env->aux = (unsigned char *)aes_new_cipher();
  } else if (! crypto_cipher_evp_cipher(type,0)) 
    /* This is not an openssl cipher */
    goto err;
  else {
    env->aux = (unsigned char *)tor_malloc(sizeof(EVP_CIPHER_CTX));
    EVP_CIPHER_CTX_init((EVP_CIPHER_CTX *)env->aux);
  }

  if(iv_len)
    env->iv = (unsigned char *)tor_malloc(iv_len);

  if(key_len)
    env->key = (unsigned char *)tor_malloc(key_len);
  
  return env;
err:
  if (env->key)
    free(env->key);
  if (env->iv)
    free(env->iv);
  if (env->aux)
    free(env->aux);
  if (env)
    free(env);
  return NULL;
}

void crypto_free_cipher_env(crypto_cipher_env_t *env)
{
  assert(env);

  if (env->type == CRYPTO_CIPHER_AES_CTR) {
    assert(env->aux);
    aes_free_cipher((aes_cnt_cipher_t*)env->aux);
    env->aux = NULL;
  } else if (crypto_cipher_evp_cipher(env->type,0)) {
    /* This is an openssl cipher */
    assert(env->aux);
    EVP_CIPHER_CTX_cleanup((EVP_CIPHER_CTX *)env->aux);
  }

  if (env->aux)
    free((void *)env->aux);
  if (env->iv) 
    free((void *)env->iv);
  if (env->key)
    free((void *)env->key);

  free((void *)env);
}

/* public key crypto */
int crypto_pk_generate_key(crypto_pk_env_t *env)
{
  assert(env);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
    if (env->key)
      RSA_free((RSA *)env->key);
    env->key = (unsigned char *)RSA_generate_key(1024,65537, NULL, NULL);
    if (!env->key)
      return -1;
    break;
    default:
    return -1;
  }
  
  return 0;
}

int crypto_pk_read_private_key_from_file(crypto_pk_env_t *env, FILE *src)
{
  assert(env && src);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
    if (env->key)
      RSA_free((RSA *)env->key);
    env->key = (unsigned char *)PEM_read_RSAPrivateKey(src, NULL, NULL, NULL);
    if (!env->key)
      return -1;
    break;
    default :
    return -1;
  }
  
  return 0;
}

int crypto_pk_read_private_key_from_filename(crypto_pk_env_t *env, unsigned char *keyfile)
{
  FILE *f_pr;
  int retval = 0;
 
  assert(env && keyfile);
  
  if (strspn(keyfile,CONFIG_LEGAL_FILENAME_CHARACTERS) == strlen(keyfile)) /* filename contains legal characters only */
  {
    /* open the keyfile */
    f_pr=fopen(keyfile,"rb");
    if (!f_pr)
      return -1;
    
    /* read the private key */
    retval = crypto_pk_read_private_key_from_file(env, f_pr);
    fclose(f_pr);
    if (retval == -1)
    {
      log_fn(LOG_ERR,"Error reading private key : %s",crypto_perror());
      return -1;
    }
      
    /* check the private key */
    retval = crypto_pk_check_key(env);
    if (retval == 0)
    {
      log_fn(LOG_ERR,"Private key read but is invalid : %s.", crypto_perror());
      return -1;
    }
    else if (retval == -1)
    {
      log_fn(LOG_ERR,"Private key read but validity checking failed : %s",crypto_perror());
      return -1;
    }
    else if (retval == 1)
    {
      return 0;
    }
  } /* filename contains legal characters only */
  
  return -1; /* report error */
}

int crypto_pk_read_public_key_from_file(crypto_pk_env_t *env, FILE *src)
{
  assert(env && src);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
    if(env->key)
      RSA_free((RSA *)env->key); 
    env->key = (unsigned char *)PEM_read_RSAPublicKey(src, NULL, NULL, NULL);
    if (!env->key)
      return -1;
    break;
    default :
    return -1;
  }
  
  return 0;
}

int crypto_pk_write_public_key_to_string(crypto_pk_env_t *env, char **dest, int *len) {
  BUF_MEM *buf;
  BIO *b; 

  assert(env && env->key && dest);

  switch(env->type) {
    case CRYPTO_PK_RSA:

        b = BIO_new(BIO_s_mem()); /* Create a memory BIO */

        /* Now you can treat b as if it were a file.  Just use the
         * PEM_*_bio_* functions instead of the non-bio variants.
         */
        if(!PEM_write_bio_RSAPublicKey(b, (RSA *)env->key))
          return -1;

        BIO_get_mem_ptr(b, &buf);
        BIO_set_close(b, BIO_NOCLOSE); /* so BIO_free doesn't free buf */
        BIO_free(b);

        *dest = tor_malloc(buf->length+1);
        memcpy(*dest, buf->data, buf->length);
        (*dest)[buf->length] = 0; /* null terminate it */
        *len = buf->length;
        BUF_MEM_free(buf);

      break;
    default:
      return -1;
  }
  
  return 0;
}

int crypto_pk_read_public_key_from_string(crypto_pk_env_t *env, char *src, int len) {
  BIO *b; 

  assert(env && src);

  switch(env->type) {
    case CRYPTO_PK_RSA:
      b = BIO_new(BIO_s_mem()); /* Create a memory BIO */

      BIO_write(b, src, len);

      RSA_free((RSA *)env->key); 
      env->key = (unsigned char *)PEM_read_bio_RSAPublicKey(b, NULL, NULL, NULL);
      if(!env->key)
        return -1;

      BIO_free(b);
      break;
    default:
      return -1;
  }
  
  return 0;
}

int crypto_pk_write_private_key_to_file(crypto_pk_env_t *env, FILE *dest)
{
  assert(env && dest);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
      if (!env->key)
        return -1;
      if (PEM_write_RSAPrivateKey(dest, (RSA *)env->key, NULL, NULL, 0,0, NULL) == 0)
        return -1;
      break;
    default :
      return -1;
  }
  
  return 0;
}
int crypto_pk_write_public_key_to_file(crypto_pk_env_t *env, FILE *dest)
{
  assert(env && dest);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
      if (!env->key)
        return -1;
      if (PEM_write_RSAPublicKey(dest, (RSA *)env->key) == 0)
        return -1;
      break;
    default :
      return -1;
  }
  
  return 0;
}

int crypto_pk_check_key(crypto_pk_env_t *env)
{
  assert(env);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
      return RSA_check_key((RSA *)env->key);
    default:
      return -1;
  }
}

int crypto_pk_cmp_keys(crypto_pk_env_t *a, crypto_pk_env_t *b) {
  int result; 
  
  if (!a || !b)
    return -1;
  
  if (!a->key || !b->key)
    return -1;
  
  if (a->type != b->type)
    return -1;
  
  switch(a->type) {
    case CRYPTO_PK_RSA:
      assert(((RSA *)a->key)->n && ((RSA *)a->key)->e && ((RSA *)b->key)->n && ((RSA *)b->key)->e);
      result = BN_cmp(((RSA *)a->key)->n, ((RSA *)b->key)->n);
      if (result)
        return result;
      return BN_cmp(((RSA *)a->key)->e, ((RSA *)b->key)->e);
    default:
      return -1;
  }
}

int crypto_pk_keysize(crypto_pk_env_t *env)
{
  assert(env && env->key);
  
  return RSA_size((RSA *)env->key);
}

crypto_pk_env_t *crypto_pk_dup_key(crypto_pk_env_t *env) {
  assert(env && env->key);

  switch(env->type) {
    case CRYPTO_PK_RSA:
      env->refs++; 
      break;
    default:
      return NULL; 
  }
  
  return env;
}

int crypto_pk_public_encrypt(crypto_pk_env_t *env, unsigned char *from, int fromlen, unsigned char *to, int padding)
{
  assert(env && from && to);
  
  switch(env->type) {
    case CRYPTO_PK_RSA:
      return RSA_public_encrypt(fromlen, from, to, (RSA *)env->key, padding);
    default:
      return -1;
  }
}

int crypto_pk_private_decrypt(crypto_pk_env_t *env, unsigned char *from, int fromlen, unsigned char *to, int padding)
{
  assert(env && from && to);

  switch(env->type) {
    case CRYPTO_PK_RSA:
      if (!(((RSA*)env->key)->p))
        return -1;
      return RSA_private_decrypt(fromlen, from, to, (RSA *)env->key, padding);
    default:
      return -1;
  }
}

int crypto_pk_public_checksig(crypto_pk_env_t *env, unsigned char *from, int fromlen, unsigned char *to)
{
  assert(env && from && to);

  switch(env->type) {
    case CRYPTO_PK_RSA:
      return RSA_public_decrypt(fromlen, from, to, (RSA *)env->key, 
			      RSA_PKCS1_PADDING);
    default:
      return -1;
  }
}

int crypto_pk_private_sign(crypto_pk_env_t *env, unsigned char *from, int fromlen, unsigned char *to)
{
  assert(env && from && to);

  switch(env->type) {
    case CRYPTO_PK_RSA:
      if (!(((RSA*)env->key)->p))
        return -1;
      return RSA_private_encrypt(fromlen, from, to, (RSA *)env->key, 
			       RSA_PKCS1_PADDING);
    default:
      return -1;
  }
}

/* symmetric crypto */
int crypto_cipher_generate_key(crypto_cipher_env_t *env)
{
  int key_len;
  assert(env);

  key_len = crypto_cipher_key_length(env->type);

  if (key_len > 0)
    return crypto_rand(key_len, env->key);
  else if (key_len == 0)
    return 0;
  else
    return -1;
}

int crypto_cipher_set_iv(crypto_cipher_env_t *env, unsigned char *iv)
{
  int iv_len;
  assert(env && iv);
  
  iv_len = crypto_cipher_iv_length(env->type);
  if (!iv_len)
    return 0;

  if (!env->iv)
    return -1;

  memcpy((void*)env->iv, (void*)iv, iv_len);
  
  return 0;
}

int crypto_cipher_set_key(crypto_cipher_env_t *env, unsigned char *key)
{
  int key_len;
  assert(env && key);

  key_len = crypto_cipher_key_length(env->type);
  if (!key_len)
    return 0;

  if (!env->key)
    return -1;

  memcpy((void*)env->key, (void*)key, key_len);
  
  return 0;
}

unsigned char *crypto_cipher_get_key(crypto_cipher_env_t *env)
{
  return env->key;
}

int crypto_cipher_encrypt_init_cipher(crypto_cipher_env_t *env)
{
  assert(env);
  
  if (crypto_cipher_evp_cipher(env->type, 1)) {
    RETURN_SSL_OUTCOME(EVP_EncryptInit((EVP_CIPHER_CTX *)env->aux,
                                       crypto_cipher_evp_cipher(env->type, 1),
                                       env->key, env->iv));
  } else if (env->type == CRYPTO_CIPHER_AES_CTR) {
    aes_set_key((aes_cnt_cipher_t*)env->aux, env->key, 128);
    return 0;
  } else {
    return -1;
  }
}

int crypto_cipher_decrypt_init_cipher(crypto_cipher_env_t *env)
{
  assert(env);

  if (crypto_cipher_evp_cipher(env->type, 0)) {
    RETURN_SSL_OUTCOME(EVP_EncryptInit((EVP_CIPHER_CTX *)env->aux,
                                       crypto_cipher_evp_cipher(env->type, 0),
                                       env->key, env->iv));
  } else if (env->type == CRYPTO_CIPHER_AES_CTR) {
    aes_set_key((aes_cnt_cipher_t*)env->aux, env->key, 128);
    return 0;
  } else {
    return -1;
  }
}

int crypto_cipher_encrypt(crypto_cipher_env_t *env, unsigned char *from, unsigned int fromlen, unsigned char *to)
{
  int tolen;
  
  assert(env && from && to);
  
  if (env->type == CRYPTO_CIPHER_AES_CTR) {
    aes_crypt((aes_cnt_cipher_t*)env->aux, from, fromlen, to);
    return 0;
  } else {
    RETURN_SSL_OUTCOME(EVP_EncryptUpdate((EVP_CIPHER_CTX *)env->aux, to, &tolen, from, fromlen));
  }
}

int crypto_cipher_decrypt(crypto_cipher_env_t *env, unsigned char *from, unsigned int fromlen, unsigned char *to)
{
  int tolen;
  
  assert(env && from && to);

  if (env->type == CRYPTO_CIPHER_AES_CTR) {
    aes_crypt((aes_cnt_cipher_t*)env->aux, from, fromlen, to);
    return 0;
  } else {  
    RETURN_SSL_OUTCOME(EVP_DecryptUpdate((EVP_CIPHER_CTX *)env->aux, to, &tolen, from, fromlen));
  }
}

int
crypto_cipher_advance(crypto_cipher_env_t *env, long delta)
{
  if (env->type == CRYPTO_CIPHER_AES_CTR) {
    aes_adjust_counter((aes_cnt_cipher_t*)env->aux, delta);
    return 0;
  } else {  
    return -1;
  }
}


/* SHA-1 */
int crypto_SHA_digest(unsigned char *m, int len, unsigned char *digest)
{
  assert(m && digest);
  return (SHA1(m,len,digest) == NULL);
}

static BIGNUM *dh_param_p = NULL;
static BIGNUM *dh_param_g = NULL;


static void init_dh_param() {
  BIGNUM *p, *g;
  int r;
  if (dh_param_p && dh_param_g)
    return;
  
  p = BN_new();
  g = BN_new();
  assert(p && g);

#if 0 
  /* This is from draft-ietf-ipsec-ike-modp-groups-05.txt.  It's a safe
     prime, and supposedly it equals:
      2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }
  */
  r = BN_hex2bn(&p, 
		"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"
		"29024E088A67CC74020BBEA63B139B22514A08798E3404DD"
		"EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"
		"E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED"
		"EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D"
		"C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"
		"83655D23DCA3AD961C62F356208552BB9ED529077096966D"
		"670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF");
#endif

  /* 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 }.
  */
  /* See also rfc 3536 */
  r = BN_hex2bn(&p,
		"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E08"
		"8A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B"
		"302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9"
		"A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE6"
		"49286651ECE65381FFFFFFFFFFFFFFFF");
  assert(r);

  r = BN_set_word(g, 2);
  assert(r);
  dh_param_p = p;
  dh_param_g = g;
}

crypto_dh_env_t *crypto_dh_new()
{
  crypto_dh_env_t *res = NULL;

  if (!dh_param_p)
    init_dh_param();
    
  res = tor_malloc(sizeof(crypto_dh_env_t));
  res->dh = NULL;

  if (!(res->dh = DH_new()))
    goto err;

  if (!(res->dh->p = BN_dup(dh_param_p)))
    goto err;

  if (!(res->dh->g = BN_dup(dh_param_g)))
    goto err;

  return res;
 err:
  if (res && res->dh) DH_free(res->dh); /* frees p and g too */
  if (res) free(res);
  return NULL;
}
int crypto_dh_get_bytes(crypto_dh_env_t *dh)
{
  assert(dh);
  return DH_size(dh->dh);
}
int crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey, int pubkey_len)
{
  int bytes;
  assert(dh);
  if (!DH_generate_key(dh->dh))
    return -1;
  
  assert(dh->dh->pub_key);
  bytes = BN_num_bytes(dh->dh->pub_key);
  if (pubkey_len < bytes)
    return -1;
  
  memset(pubkey, 0, pubkey_len);
  BN_bn2bin(dh->dh->pub_key, pubkey+(pubkey_len-bytes));

  return 0;
}

#undef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))
int crypto_dh_compute_secret(crypto_dh_env_t *dh, 
			     char *pubkey, int pubkey_len,
			     char *secret_out, int secret_bytes_out)
{
  unsigned char hash[20];
  unsigned char *secret_tmp = NULL;
  BIGNUM *pubkey_bn = NULL;
  int secret_len;
  int i;
  assert(dh);
  assert(secret_bytes_out/20 <= 255);

  if (!(pubkey_bn = BN_bin2bn(pubkey, pubkey_len, NULL)))
    goto error;
  secret_tmp = tor_malloc(crypto_dh_get_bytes(dh)+1);
  secret_len = DH_compute_key(secret_tmp, pubkey_bn, dh->dh);
  for (i = 0; i < secret_bytes_out; i += 20) {
    secret_tmp[secret_len] = (unsigned char) i/20;
    if (crypto_SHA_digest(secret_tmp, secret_len+1, hash))
      goto error;
    memcpy(secret_out+i, hash, MIN(20, secret_bytes_out-i));
  }
  secret_len = secret_bytes_out;

  goto done;
 error:
  secret_len = -1;
 done:
  if (pubkey_bn)
    BN_free(pubkey_bn);
  if (secret_tmp)
    free(secret_tmp);
  return secret_len;
}
void crypto_dh_free(crypto_dh_env_t *dh)
{
  assert(dh && dh->dh);
  DH_free(dh->dh);
  free(dh);
}

/* random numbers */
int crypto_seed_rng()
{
  static char *filenames[] = { 
    "/dev/srandom", "/dev/urandom", "/dev/random", NULL
  };
  int i, n;
  char buf[21];
  FILE *f;
  
  for (i = 0; filenames[i]; ++i) {
    f = fopen(filenames[i], "rb");
    if (!f) continue;
    log_fn(LOG_INFO, "Seeding RNG from %s", filenames[i]);
    n = fread(buf, 1, 20, f);
    fclose(f);
    if (n != 20) {
      log_fn(LOG_INFO, "Error reading from entropy source");
      return -1;
    }
    RAND_seed(buf, 20);
    return 0;
  }

  log_fn(LOG_INFO, "Cannot seed RNG -- no entropy source found.");
  return -1;
}

int crypto_rand(unsigned int n, unsigned char *to)
{
  assert(to);
  return (RAND_bytes(to, n) != 1);
}

int crypto_pseudo_rand(unsigned int n, unsigned char *to)
{
  assert(to);
  return (RAND_pseudo_bytes(to, n) == -1);
}

/* errors */
char *crypto_perror()
{
  return (char *)ERR_reason_error_string(ERR_get_error());
}

int 
base64_encode(char *dest, int destlen, char *src, int srclen)
{
  EVP_ENCODE_CTX ctx;
  int len, ret;
  
  /* 48 bytes of input -> 64 bytes of output plus newline. 
     Plus one more byte, in case I'm wrong.
  */
  if (destlen < ((srclen/48)+1)*66)
    return -1;

  EVP_EncodeInit(&ctx);
  EVP_EncodeUpdate(&ctx, dest, &len, src, srclen);
  EVP_EncodeFinal(&ctx, dest+len, &ret);
  ret += len;
  return ret;
}
int 
base64_decode(char *dest, int destlen, char *src, int srclen)
{
  EVP_ENCODE_CTX ctx;
  int len, ret;
  /* 64 bytes of input -> *up to* 48 bytes of output.
     Plus one more byte, in caes I'm wrong.
  */
  if (destlen < ((srclen/64)+1)*49)
    return -1;

  EVP_DecodeInit(&ctx);
  EVP_DecodeUpdate(&ctx, dest, &len, src, srclen);
  EVP_DecodeFinal(&ctx, dest, &ret);
  ret += len;
  return ret;
}