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openssl-esp.c
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openssl-esp.c
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/*
* OpenConnect (SSL + DTLS) VPN client
*
* Copyright © 2008-2015 Intel Corporation.
*
* Author: David Woodhouse <[email protected]>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* version 2.1, as published by the Free Software Foundation.
*
* 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
* Lesser General Public License for more details.
*/
#include <config.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include "openconnect-internal.h"
#include <openssl/evp.h>
#include <openssl/rand.h>
void destroy_esp_ciphers(struct esp *esp)
{
EVP_CIPHER_CTX_cleanup(&esp->cipher);
HMAC_CTX_cleanup(&esp->hmac);
}
static int init_esp_ciphers(struct openconnect_info *vpninfo, struct esp *esp,
const EVP_MD *macalg, const EVP_CIPHER *encalg, int decrypt)
{
int ret;
destroy_esp_ciphers(esp);
EVP_CIPHER_CTX_init(&esp->cipher);
if (decrypt)
ret = EVP_DecryptInit_ex(&esp->cipher, encalg, NULL, esp->secrets, NULL);
else
ret = EVP_EncryptInit_ex(&esp->cipher, encalg, NULL, esp->secrets, NULL);
if (!ret) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to initialise ESP cipher:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EIO;
}
EVP_CIPHER_CTX_set_padding(&esp->cipher, 0);
HMAC_CTX_init(&esp->hmac);
if (!HMAC_Init_ex(&esp->hmac, esp->secrets + EVP_CIPHER_key_length(encalg),
EVP_MD_size(macalg), macalg, NULL)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to initialize ESP HMAC\n"));
openconnect_report_ssl_errors(vpninfo);
destroy_esp_ciphers(esp);
}
esp->seq = 0;
esp->seq_backlog = 0;
return 0;
}
int setup_esp_keys(struct openconnect_info *vpninfo)
{
struct esp *esp_in;
const EVP_CIPHER *encalg;
const EVP_MD *macalg;
int ret;
if (vpninfo->dtls_state == DTLS_DISABLED)
return -EOPNOTSUPP;
if (!vpninfo->dtls_addr)
return -EINVAL;
switch (vpninfo->esp_enc) {
case 0x02:
encalg = EVP_aes_128_cbc();
break;
case 0x05:
encalg = EVP_aes_256_cbc();
break;
default:
return -EINVAL;
}
switch (vpninfo->esp_hmac) {
case 0x01:
macalg = EVP_md5();
break;
case 0x02:
macalg = EVP_sha1();
break;
default:
return -EINVAL;
}
vpninfo->old_esp_maxseq = vpninfo->esp_in[vpninfo->current_esp_in].seq + 32;
vpninfo->current_esp_in ^= 1;
esp_in = &vpninfo->esp_in[vpninfo->current_esp_in];
if (!RAND_bytes((void *)&esp_in->spi, sizeof(esp_in->spi)) ||
!RAND_bytes((void *)&esp_in->secrets, sizeof(esp_in->secrets))) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to generate random keys for ESP:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EIO;
}
ret = init_esp_ciphers(vpninfo, &vpninfo->esp_out, macalg, encalg, 0);
if (ret)
return ret;
ret = init_esp_ciphers(vpninfo, esp_in, macalg, encalg, 1);
if (ret) {
destroy_esp_ciphers(&vpninfo->esp_out);
return ret;
}
if (vpninfo->dtls_state == DTLS_NOSECRET)
vpninfo->dtls_state = DTLS_SECRET;
vpninfo->pkt_trailer = 16 + 20; /* 16 for pad, 20 for HMAC (of which we use 16) */
return 0;
}
/* pkt->len shall be the *payload* length. Omitting the header and the 12-byte HMAC */
int decrypt_esp_packet(struct openconnect_info *vpninfo, struct esp *esp, struct pkt *pkt)
{
unsigned char hmac_buf[20];
unsigned int hmac_len = sizeof(hmac_buf);
int crypt_len = pkt->len;
HMAC_CTX hmac_ctx;
HMAC_CTX_copy(&hmac_ctx, &esp->hmac);
HMAC_Update(&hmac_ctx, (void *)&pkt->esp, sizeof(pkt->esp) + pkt->len);
HMAC_Final(&hmac_ctx, hmac_buf, &hmac_len);
HMAC_CTX_cleanup(&hmac_ctx);
if (memcmp(hmac_buf, pkt->data + pkt->len, 12)) {
vpn_progress(vpninfo, PRG_DEBUG,
_("Received ESP packet with invalid HMAC\n"));
return -EINVAL;
}
/* Why in $DEITY's name would you ever *not* set this? Perhaps we
* should do th check anyway, but only warn instead of discarding
* the packet? */
if (vpninfo->esp_replay_protect &&
verify_packet_seqno(vpninfo, esp, ntohl(pkt->esp.seq)))
return -EINVAL;
if (!EVP_DecryptInit_ex(&esp->cipher, NULL, NULL, NULL,
pkt->esp.iv)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set up decryption context for ESP packet:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EINVAL;
}
if (!EVP_DecryptUpdate(&esp->cipher, pkt->data, &crypt_len,
pkt->data, pkt->len)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to decrypt ESP packet:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EINVAL;
}
return 0;
}
int encrypt_esp_packet(struct openconnect_info *vpninfo, struct pkt *pkt)
{
int i, padlen;
const int blksize = 16;
unsigned int hmac_len = 20;
int crypt_len;
HMAC_CTX hmac_ctx;
/* This gets much more fun if the IV is variable-length */
pkt->esp.spi = vpninfo->esp_out.spi;
pkt->esp.seq = htonl(vpninfo->esp_out.seq++);
if (!RAND_bytes((void *)&pkt->esp.iv, sizeof(pkt->esp.iv))) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to generate random IV for ESP packet:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EIO;
}
padlen = blksize - 1 - ((pkt->len + 1) % blksize);
for (i=0; i<padlen; i++)
pkt->data[pkt->len + i] = i + 1;
pkt->data[pkt->len + padlen] = padlen;
pkt->data[pkt->len + padlen + 1] = 0x04; /* Legacy IP */
if (!EVP_EncryptInit_ex(&vpninfo->esp_out.cipher, NULL, NULL, NULL,
pkt->esp.iv)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to set up encryption context for ESP packet:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EINVAL;
}
crypt_len = pkt->len + padlen + 2;
if (!EVP_EncryptUpdate(&vpninfo->esp_out.cipher, pkt->data, &crypt_len,
pkt->data, crypt_len)) {
vpn_progress(vpninfo, PRG_ERR,
_("Failed to encrypt ESP packet:\n"));
openconnect_report_ssl_errors(vpninfo);
return -EINVAL;
}
HMAC_CTX_copy(&hmac_ctx, &vpninfo->esp_out.hmac);
HMAC_Update(&hmac_ctx, (void *)&pkt->esp, sizeof(pkt->esp) + crypt_len);
HMAC_Final(&hmac_ctx, pkt->data + crypt_len, &hmac_len);
HMAC_CTX_cleanup(&hmac_ctx);
return sizeof(pkt->esp) + crypt_len + 12;
}