/*
* ekt.c
*
* Encrypted Key Transport for SRTP
*
* David McGrew
* Cisco Systems, Inc.
*/
/*
*
* Copyright (c) 2001-2006 Cisco Systems, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* Neither the name of the Cisco Systems, Inc. nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#include "err.h"
#include "srtp_priv.h"
#include "ekt.h"
extern debug_module_t mod_srtp;
/*
* The EKT Authentication Tag format.
*
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* : Base Authentication Tag :
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* : Encrypted Master Key :
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Rollover Counter |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | Initial Sequence Number | Security Parameter Index |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*
*/
#define EKT_OCTETS_AFTER_BASE_TAG 24
#define EKT_OCTETS_AFTER_EMK 8
#define EKT_OCTETS_AFTER_ROC 4
#define EKT_SPI_LEN 2
unsigned
ekt_octets_after_base_tag(ekt_stream_t ekt) {
/*
* if the pointer ekt is NULL, then EKT is not in effect, so we
* indicate this by returning zero
*/
if (!ekt)
return 0;
switch(ekt->data->ekt_cipher_type) {
case EKT_CIPHER_AES_128_ECB:
return 16 + EKT_OCTETS_AFTER_EMK;
break;
default:
break;
}
return 0;
}
static inline ekt_spi_t
srtcp_packet_get_ekt_spi(const uint8_t *packet_start, unsigned pkt_octet_len) {
const uint8_t *spi_location;
spi_location = packet_start + (pkt_octet_len - EKT_SPI_LEN);
return *((const ekt_spi_t *)spi_location);
}
static inline uint32_t
srtcp_packet_get_ekt_roc(const uint8_t *packet_start, unsigned pkt_octet_len) {
const uint8_t *roc_location;
roc_location = packet_start + (pkt_octet_len - EKT_OCTETS_AFTER_ROC);
return *((const uint32_t *)roc_location);
}
static inline const uint8_t *
srtcp_packet_get_emk_location(const uint8_t *packet_start,
unsigned pkt_octet_len) {
const uint8_t *location;
location = packet_start + (pkt_octet_len - EKT_OCTETS_AFTER_BASE_TAG);
return location;
}
err_status_t
ekt_alloc(ekt_stream_t *stream_data, ekt_policy_t policy) {
/*
* if the policy pointer is NULL, then EKT is not in use
* so we just set the EKT stream data pointer to NULL
*/
if (!policy) {
*stream_data = NULL;
return err_status_ok;
}
/* TODO */
*stream_data = NULL;
return err_status_ok;
}
err_status_t
ekt_stream_init_from_policy(ekt_stream_t stream_data, ekt_policy_t policy) {
if (!stream_data)
return err_status_ok;
return err_status_ok;
}
void
aes_decrypt_with_raw_key(void *ciphertext, const void *key) {
aes_expanded_key_t expanded_key;
aes_expand_decryption_key(key, expanded_key);
aes_decrypt(ciphertext, expanded_key);
}
/*
* The function srtp_stream_init_from_ekt() initializes a stream using
* the EKT data from an SRTCP trailer.
*/
err_status_t
srtp_stream_init_from_ekt(srtp_stream_t stream,
const void *srtcp_hdr,
unsigned pkt_octet_len) {
err_status_t err;
const uint8_t *master_key;
srtp_policy_t srtp_policy;
unsigned master_key_len;
uint32_t roc;
/*
* NOTE: at present, we only support a single ekt_policy at a time.
*/
if (stream->ekt->data->spi !=
srtcp_packet_get_ekt_spi(srtcp_hdr, pkt_octet_len))
return err_status_no_ctx;
if (stream->ekt->data->ekt_cipher_type != EKT_CIPHER_AES_128_ECB)
return err_status_bad_param;
master_key_len = 16;
/* decrypt the Encrypted Master Key field */
master_key = srtcp_packet_get_emk_location(srtcp_hdr, pkt_octet_len);
aes_decrypt_with_raw_key((void*)master_key, stream->ekt->data->ekt_dec_key);
/* set the SRTP ROC */
roc = srtcp_packet_get_ekt_roc(srtcp_hdr, pkt_octet_len);
err = rdbx_set_roc(&stream->rtp_rdbx, roc);
if (err) return err;
err = srtp_stream_init(stream, &srtp_policy);
if (err) return err;
return err_status_ok;
}
void
ekt_write_data(ekt_stream_t ekt,
void *base_tag,
unsigned base_tag_len,
int *packet_len,
xtd_seq_num_t pkt_index) {
uint32_t roc;
uint16_t isn;
unsigned emk_len;
uint8_t *packet;
/* if the pointer ekt is NULL, then EKT is not in effect */
if (!ekt) {
debug_print(mod_srtp, "EKT not in use", NULL);
return;
}
/* write zeros into the location of the base tag */
octet_string_set_to_zero(base_tag, base_tag_len);
packet = (uint8_t*)base_tag + base_tag_len;
/* copy encrypted master key into packet */
emk_len = ekt_octets_after_base_tag(ekt);
memcpy(packet, ekt->encrypted_master_key, emk_len);
debug_print(mod_srtp, "writing EKT EMK: %s,",
octet_string_hex_string(packet, emk_len));
packet += emk_len;
/* copy ROC into packet */
roc = (uint32_t)(pkt_index >> 16);
*((uint32_t *)packet) = be32_to_cpu(roc);
debug_print(mod_srtp, "writing EKT ROC: %s,",
octet_string_hex_string(packet, sizeof(roc)));
packet += sizeof(roc);
/* copy ISN into packet */
isn = (uint16_t)pkt_index;
*((uint16_t *)packet) = htons(isn);
debug_print(mod_srtp, "writing EKT ISN: %s,",
octet_string_hex_string(packet, sizeof(isn)));
packet += sizeof(isn);
/* copy SPI into packet */
*((uint16_t *)packet) = htons(ekt->data->spi);
debug_print(mod_srtp, "writing EKT SPI: %s,",
octet_string_hex_string(packet, sizeof(ekt->data->spi)));
/* increase packet length appropriately */
*packet_len += EKT_OCTETS_AFTER_EMK + emk_len;
}
/*
* The function call srtcp_ekt_trailer(ekt, auth_len, auth_tag )
*
* If the pointer ekt is NULL, then the other inputs are unaffected.
*
* auth_tag is a pointer to the pointer to the location of the
* authentication tag in the packet. If EKT is in effect, then the
* auth_tag pointer is set to the location
*/
void
srtcp_ekt_trailer(ekt_stream_t ekt,
unsigned *auth_len,
void **auth_tag,
void *tag_copy) {
/*
* if there is no EKT policy, then the other inputs are unaffected
*/
if (!ekt)
return;
/* copy auth_tag into temporary location */
}