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n2n/transform_aes.c
emanuele-f d76cb64d0f Fix seed debug print
2019-06-03 10:16:42 +02:00

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/**
* (C) 2007-18 - ntop.org and contributors
*
* 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 3 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; if not see see <http://www.gnu.org/licenses/>
*
*/
#include "n2n.h"
#include "n2n_transforms.h"
#ifdef N2N_HAVE_AES
#include "openssl/aes.h"
#include "openssl/sha.h"
#define N2N_AES_TRANSFORM_VERSION 1 /* version of the transform encoding */
#define N2N_AES_IVEC_SIZE 32 /* Enough space for biggest AES ivec */
#define AES256_KEY_BYTES (256/8)
#define AES192_KEY_BYTES (192/8)
#define AES128_KEY_BYTES (128/8)
/* AES plaintext preamble */
#define TRANSOP_AES_VER_SIZE 1 /* Support minor variants in encoding in one module. */
#define TRANSOP_AES_SA_SIZE 4
#define TRANSOP_AES_IV_SEED_SIZE 8
#define TRANSOP_AES_PREAMBLE_SIZE (TRANSOP_AES_VER_SIZE + TRANSOP_AES_SA_SIZE + TRANSOP_AES_IV_SEED_SIZE)
/* AES ciphertext preamble */
#define TRANSOP_AES_NONCE_SIZE 4
typedef unsigned char n2n_aes_ivec_t[N2N_AES_IVEC_SIZE];
typedef struct transop_aes {
AES_KEY enc_key; /* tx key */
AES_KEY dec_key; /* tx key */
AES_KEY iv_enc_key; /* key used to encrypt the IV */
uint8_t iv_ext_val[AES128_KEY_BYTES]; /* key used to extend the random IV seed to full block size */
} transop_aes_t;
struct sha512_keybuf {
uint8_t enc_dec_key[AES256_KEY_BYTES]; /* The key to use for AES CBC encryption/decryption */
uint8_t iv_enc_key[AES128_KEY_BYTES]; /* The key to use to encrypt the IV with AES ECB */
uint8_t iv_ext_val[AES128_KEY_BYTES]; /* A value to extend the IV seed */
}; /* size: SHA512_DIGEST_LENGTH */
static int transop_deinit_aes(n2n_trans_op_t *arg) {
transop_aes_t *priv = (transop_aes_t *)arg->priv;
if(priv)
free(priv);
return 0;
}
/* Return the best acceptable AES key size (in bytes) given an input keysize.
*
* The value returned will be one of AES128_KEY_BYTES, AES192_KEY_BYTES or
* AES256_KEY_BYTES.
*/
static size_t aes_best_keysize(size_t numBytes)
{
if (numBytes >= AES256_KEY_BYTES)
{
return AES256_KEY_BYTES;
}
else if (numBytes >= AES192_KEY_BYTES)
{
return AES192_KEY_BYTES;
}
else
{
return AES128_KEY_BYTES;
}
}
static void set_aes_cbc_iv(transop_aes_t *priv, n2n_aes_ivec_t ivec, uint64_t iv_seed) {
uint8_t iv_full[AES_BLOCK_SIZE];
/* Extend the seed to full block size via the fixed ext value */
memcpy(iv_full, priv->iv_ext_val, sizeof(iv_seed)); // note: only 64bits used of 128 available
memcpy(iv_full + sizeof(iv_seed), &iv_seed, sizeof(iv_seed));
/* Encrypt the IV with secret key to make it unpredictable.
* As discussed in https://github.com/ntop/n2n/issues/72, it's important to
* have an unpredictable IV since the initial part of the packet plaintext
* can be easily reconstructed from plaintext headers and used by an attacker
* to perform differential analysis.
*/
AES_ecb_encrypt(iv_full, ivec, &priv->iv_enc_key, AES_ENCRYPT);
}
/** The aes packet format consists of:
*
* - a 8-bit aes encoding version in clear text
* - a 32-bit SA number in clear text
* - a 64-bit random IV seed
* - ciphertext encrypted from a 32-bit nonce followed by the payload.
*
* [V|SSSS|II|nnnnDDDDDDDDDDDDDDDDDDDDD]
* |<------ encrypted ------>|
*/
static int transop_encode_aes( n2n_trans_op_t * arg,
uint8_t * outbuf,
size_t out_len,
const uint8_t * inbuf,
size_t in_len,
const uint8_t * peer_mac)
{
int len2=-1;
transop_aes_t * priv = (transop_aes_t *)arg->priv;
uint8_t assembly[N2N_PKT_BUF_SIZE] = {0};
uint32_t * pnonce;
if ( (in_len + TRANSOP_AES_NONCE_SIZE) <= N2N_PKT_BUF_SIZE) {
if ( (in_len + TRANSOP_AES_NONCE_SIZE + TRANSOP_AES_PREAMBLE_SIZE) <= out_len) {
int len=-1;
size_t idx=0;
size_t tx_sa_num = 0; // Not used
uint64_t iv_seed = 0;
uint8_t padding = 0;
n2n_aes_ivec_t enc_ivec = {0};
traceEvent(TRACE_DEBUG, "encode_aes %lu", in_len);
/* Encode the aes format version. */
encode_uint8( outbuf, &idx, N2N_AES_TRANSFORM_VERSION);
/* Encode the security association (SA) number */
encode_uint32( outbuf, &idx, tx_sa_num); // Not used
/* Generate and encode the IV seed.
* Using two calls to rand() because RAND_MAX is usually < 64bit
* (e.g. linux) and sometimes < 32bit (e.g. Windows).
*/
iv_seed = ((((uint64_t)rand() & 0xFFFFFFFF)) << 32) | rand();
encode_buf(outbuf, &idx, &iv_seed, sizeof(iv_seed));
/* Encrypt the assembly contents and write the ciphertext after the SA. */
len = in_len + TRANSOP_AES_NONCE_SIZE;
/* The assembly buffer is a source for encrypting data. The nonce is
* written in first followed by the packet payload. The whole
* contents of assembly are encrypted. */
pnonce = (uint32_t *)assembly;
*pnonce = rand();
memcpy( assembly + TRANSOP_AES_NONCE_SIZE, inbuf, in_len);
/* Need at least one encrypted byte at the end for the padding. */
len2 = ( (len / AES_BLOCK_SIZE) + 1) * AES_BLOCK_SIZE; /* Round up to next whole AES adding at least one byte. */
padding = (len2-len);
assembly[len2 - 1] = padding;
traceEvent(TRACE_DEBUG, "padding = %u, seed = %016llx", padding, iv_seed);
set_aes_cbc_iv(priv, enc_ivec, iv_seed);
AES_cbc_encrypt( assembly, /* source */
outbuf + TRANSOP_AES_PREAMBLE_SIZE, /* dest */
len2, /* enc size */
&(priv->enc_key), enc_ivec, AES_ENCRYPT);
len2 += TRANSOP_AES_PREAMBLE_SIZE; /* size of data carried in UDP. */
} else
traceEvent(TRACE_ERROR, "encode_aes outbuf too small.");
} else
traceEvent(TRACE_ERROR, "encode_aes inbuf too big to encrypt.");
return len2;
}
/* See transop_encode_aes for packet format */
static int transop_decode_aes( n2n_trans_op_t * arg,
uint8_t * outbuf,
size_t out_len,
const uint8_t * inbuf,
size_t in_len,
const uint8_t * peer_mac) {
int len=0;
transop_aes_t * priv = (transop_aes_t *)arg->priv;
uint8_t assembly[N2N_PKT_BUF_SIZE];
if ( ( (in_len - TRANSOP_AES_PREAMBLE_SIZE) <= N2N_PKT_BUF_SIZE) /* Cipher text fits in assembly */
&& (in_len >= (TRANSOP_AES_PREAMBLE_SIZE + TRANSOP_AES_NONCE_SIZE)) /* Has at least version, SA, iv seed and nonce */
)
{
uint32_t sa_rx=0; // Not used
size_t rem=in_len;
size_t idx=0;
uint8_t aes_enc_ver=0;
uint64_t iv_seed=0;
/* Get the encoding version to make sure it is supported */
decode_uint8( &aes_enc_ver, inbuf, &rem, &idx);
if ( N2N_AES_TRANSFORM_VERSION == aes_enc_ver) {
/* Get the SA number and make sure we are decrypting with the right one. - Not used*/
decode_uint32( &sa_rx, inbuf, &rem, &idx);
/* Get the IV seed */
decode_buf((uint8_t *)&iv_seed, sizeof(iv_seed), inbuf, &rem, &idx);
traceEvent(TRACE_DEBUG, "decode_aes %lu with seed %016llx", in_len, iv_seed);
len = (in_len - TRANSOP_AES_PREAMBLE_SIZE);
if ( 0 == (len % AES_BLOCK_SIZE)) {
uint8_t padding;
n2n_aes_ivec_t dec_ivec = {0};
set_aes_cbc_iv(priv, dec_ivec, iv_seed);
AES_cbc_encrypt( (inbuf + TRANSOP_AES_PREAMBLE_SIZE),
assembly, /* destination */
len,
&(priv->dec_key),
dec_ivec, AES_DECRYPT);
/* last byte is how much was padding: max value should be
* AES_BLOCKSIZE-1 */
padding = assembly[ len-1 ] & 0xff;
if ( len >= (padding + TRANSOP_AES_NONCE_SIZE))
{
/* strictly speaking for this to be an ethernet packet
* it is going to need to be even bigger; but this is
* enough to prevent segfaults. */
traceEvent(TRACE_DEBUG, "padding = %u", padding);
len -= padding;
len -= TRANSOP_AES_NONCE_SIZE; /* size of ethernet packet */
/* Step over 4-byte random nonce value */
memcpy( outbuf,
assembly + TRANSOP_AES_NONCE_SIZE,
len);
} else
traceEvent(TRACE_WARNING, "UDP payload decryption failed.");
} else {
traceEvent(TRACE_WARNING, "Encrypted length %d is not a multiple of AES_BLOCK_SIZE (%d)", len, AES_BLOCK_SIZE);
len = 0;
}
} else
traceEvent(TRACE_ERROR, "decode_aes unsupported aes version %u.", aes_enc_ver);
} else
traceEvent(TRACE_ERROR, "decode_aes inbuf wrong size (%ul) to decrypt.", in_len);
return len;
}
static int setup_aes_key(transop_aes_t *priv, const uint8_t *key, ssize_t key_size) {
size_t aes_keysize_bytes;
size_t aes_keysize_bits;
struct sha512_keybuf keybuf;
/* Clear out any old possibly longer key matter. */
memset( &(priv->enc_key), 0, sizeof(priv->enc_key));
memset( &(priv->dec_key), 0, sizeof(priv->dec_key));
memset( &(priv->iv_enc_key), 0, sizeof(priv->iv_enc_key));
memset( &(priv->iv_ext_val), 0, sizeof(priv->iv_ext_val));
/* We still use aes_best_keysize (even not necessary since we hash the key
* into the 256bits enc_dec_key) to let the users choose the degree of encryption.
* Long keys will pick AES192 or AES256 with more robust but expensive encryption.
*/
aes_keysize_bytes = aes_best_keysize(key_size);
aes_keysize_bits = 8 * aes_keysize_bytes;
/* Hash the main key to generate subkeys */
SHA512(key, key_size, (u_char*)&keybuf);
/* setup of enc_key/dec_key, used for the CBC encryption */
AES_set_encrypt_key(keybuf.enc_dec_key, aes_keysize_bits, &(priv->enc_key));
AES_set_decrypt_key(keybuf.enc_dec_key, aes_keysize_bits, &(priv->dec_key));
/* setup of iv_enc_key and iv_ext_val, used for generating the CBC IV */
AES_set_encrypt_key(keybuf.iv_enc_key, sizeof(keybuf.iv_enc_key) * 8, &(priv->iv_enc_key));
memcpy(priv->iv_ext_val, keybuf.iv_ext_val, sizeof(keybuf.iv_ext_val));
traceEvent(TRACE_DEBUG, "AES %u bits setup completed\n",
aes_keysize_bits, key);
return(0);
}
static void transop_tick_aes(n2n_trans_op_t * arg, time_t now) {}
/* AES initialization function */
int n2n_transop_aes_cbc_init(const n2n_edge_conf_t *conf, n2n_trans_op_t *ttt) {
transop_aes_t *priv;
const u_char *encrypt_key = (const u_char *)conf->encrypt_key;
size_t encrypt_key_len = strlen(conf->encrypt_key);
memset(ttt, 0, sizeof(*ttt));
ttt->transform_id = N2N_TRANSFORM_ID_AESCBC;
ttt->tick = transop_tick_aes;
ttt->deinit = transop_deinit_aes;
ttt->fwd = transop_encode_aes;
ttt->rev = transop_decode_aes;
priv = (transop_aes_t*) calloc(1, sizeof(transop_aes_t));
if(!priv) {
traceEvent(TRACE_ERROR, "cannot allocate transop_aes_t memory");
return(-1);
}
ttt->priv = priv;
/* Setup the key */
return(setup_aes_key(priv, encrypt_key, encrypt_key_len));
}
#endif /* N2N_HAVE_AES */
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