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281 lines
8.7 KiB
C
281 lines
8.7 KiB
C
/*
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* ekt.c
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*
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* Encrypted Key Transport for SRTP
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*
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* David McGrew
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* Cisco Systems, Inc.
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*/
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/*
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*
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* Copyright (c) 2001-2017 Cisco Systems, Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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*
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* Neither the name of the Cisco Systems, Inc. nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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#include "srtp_priv.h"
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#include "err.h"
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#include "ekt.h"
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extern srtp_debug_module_t mod_srtp;
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/*
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* The EKT Authentication Tag format.
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*
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* 0 1 2 3
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* 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
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* : Base Authentication Tag :
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* : Encrypted Master Key :
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | Rollover Counter |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | Initial Sequence Number | Security Parameter Index |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*
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*/
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#define EKT_OCTETS_AFTER_BASE_TAG 24
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#define EKT_OCTETS_AFTER_EMK 8
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#define EKT_OCTETS_AFTER_ROC 4
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#define EKT_SPI_LEN 2
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unsigned srtp_ekt_octets_after_base_tag(srtp_ekt_stream_t ekt)
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{
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/*
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* if the pointer ekt is NULL, then EKT is not in effect, so we
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* indicate this by returning zero
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*/
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if (!ekt)
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return 0;
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switch (ekt->data->ekt_cipher_type) {
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case SRTP_EKT_CIPHER_AES_128_ECB:
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return 16 + EKT_OCTETS_AFTER_EMK;
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break;
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default:
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break;
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}
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return 0;
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}
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static inline srtp_ekt_spi_t srtcp_packet_get_ekt_spi(
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const uint8_t *packet_start,
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unsigned pkt_octet_len)
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{
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const uint8_t *spi_location;
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spi_location = packet_start + (pkt_octet_len - EKT_SPI_LEN);
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return *((const srtp_ekt_spi_t *)spi_location);
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}
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static inline uint32_t srtcp_packet_get_ekt_roc(const uint8_t *packet_start,
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unsigned pkt_octet_len)
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{
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const uint8_t *roc_location;
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roc_location = packet_start + (pkt_octet_len - EKT_OCTETS_AFTER_ROC);
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return *((const uint32_t *)roc_location);
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}
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static inline const uint8_t *srtcp_packet_get_emk_location(
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const uint8_t *packet_start,
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unsigned pkt_octet_len)
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{
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const uint8_t *location;
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location = packet_start + (pkt_octet_len - EKT_OCTETS_AFTER_BASE_TAG);
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return location;
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}
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srtp_err_status_t srtp_ekt_alloc(srtp_ekt_stream_t *stream_data,
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srtp_ekt_policy_t policy)
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{
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/*
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* if the policy pointer is NULL, then EKT is not in use
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* so we just set the EKT stream data pointer to NULL
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*/
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if (!policy) {
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*stream_data = NULL;
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return srtp_err_status_ok;
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}
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/* TODO */
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*stream_data = NULL;
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return srtp_err_status_ok;
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}
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srtp_err_status_t srtp_ekt_stream_init_from_policy(
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srtp_ekt_stream_t stream_data,
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srtp_ekt_policy_t policy)
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{
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if (!stream_data)
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return srtp_err_status_ok;
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return srtp_err_status_ok;
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}
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void aes_decrypt_with_raw_key(void *ciphertext, const void *key, int key_len)
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{
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#ifndef GCM
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// FIXME: need to get this working through the crypto module interface
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srtp_aes_expanded_key_t expanded_key;
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srtp_aes_expand_decryption_key(key, key_len, &expanded_key);
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srtp_aes_decrypt(ciphertext, &expanded_key);
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#endif
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}
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/*
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* The function srtp_stream_init_from_ekt() initializes a stream using
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* the EKT data from an SRTCP trailer.
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*/
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srtp_err_status_t srtp_stream_init_from_ekt(srtp_stream_t stream,
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const void *srtcp_hdr,
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unsigned pkt_octet_len)
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{
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srtp_err_status_t err;
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const uint8_t *master_key;
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srtp_policy_t srtp_policy;
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uint32_t roc;
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/*
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* NOTE: at present, we only support a single ekt_policy at a time.
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*/
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if (stream->ekt->data->spi !=
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srtcp_packet_get_ekt_spi(srtcp_hdr, pkt_octet_len))
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return srtp_err_status_no_ctx;
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if (stream->ekt->data->ekt_cipher_type != SRTP_EKT_CIPHER_AES_128_ECB)
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return srtp_err_status_bad_param;
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/* decrypt the Encrypted Master Key field */
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master_key = srtcp_packet_get_emk_location(srtcp_hdr, pkt_octet_len);
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/* FIX!? This decrypts the master key in-place, and never uses it */
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/* FIX!? It's also passing to ekt_dec_key (which is an aes_expanded_key_t)
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* to a function which expects a raw (unexpanded) key */
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aes_decrypt_with_raw_key((void *)master_key,
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&stream->ekt->data->ekt_dec_key, 16);
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/* set the SRTP ROC */
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roc = srtcp_packet_get_ekt_roc(srtcp_hdr, pkt_octet_len);
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err = srtp_rdbx_set_roc(&stream->rtp_rdbx, roc);
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if (err)
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return err;
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err = srtp_stream_init(stream, &srtp_policy);
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if (err)
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return err;
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return srtp_err_status_ok;
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}
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void srtp_ekt_write_data(srtp_ekt_stream_t ekt,
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uint8_t *base_tag,
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unsigned base_tag_len,
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int *packet_len,
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srtp_xtd_seq_num_t pkt_index)
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{
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uint32_t roc;
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uint16_t isn;
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unsigned emk_len;
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uint8_t *packet;
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/* if the pointer ekt is NULL, then EKT is not in effect */
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if (!ekt) {
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debug_print0(mod_srtp, "EKT not in use");
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return;
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}
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/* write zeros into the location of the base tag */
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octet_string_set_to_zero(base_tag, base_tag_len);
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packet = base_tag + base_tag_len;
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/* copy encrypted master key into packet */
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emk_len = srtp_ekt_octets_after_base_tag(ekt);
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memcpy(packet, ekt->encrypted_master_key, emk_len);
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debug_print(mod_srtp, "writing EKT EMK: %s,",
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srtp_octet_string_hex_string(packet, emk_len));
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packet += emk_len;
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/* copy ROC into packet */
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roc = (uint32_t)(pkt_index >> 16);
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*((uint32_t *)packet) = be32_to_cpu(roc);
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debug_print(mod_srtp, "writing EKT ROC: %s,",
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srtp_octet_string_hex_string(packet, sizeof(roc)));
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packet += sizeof(roc);
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/* copy ISN into packet */
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isn = (uint16_t)pkt_index;
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*((uint16_t *)packet) = htons(isn);
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debug_print(mod_srtp, "writing EKT ISN: %s,",
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srtp_octet_string_hex_string(packet, sizeof(isn)));
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packet += sizeof(isn);
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/* copy SPI into packet */
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*((uint16_t *)packet) = htons(ekt->data->spi);
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debug_print(mod_srtp, "writing EKT SPI: %s,",
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srtp_octet_string_hex_string(packet, sizeof(ekt->data->spi)));
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/* increase packet length appropriately */
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*packet_len += EKT_OCTETS_AFTER_EMK + emk_len;
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}
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/*
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* The function call srtcp_ekt_trailer(ekt, auth_len, auth_tag )
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*
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* If the pointer ekt is NULL, then the other inputs are unaffected.
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*
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* auth_tag is a pointer to the pointer to the location of the
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* authentication tag in the packet. If EKT is in effect, then the
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* auth_tag pointer is set to the location
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*/
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void srtcp_ekt_trailer(srtp_ekt_stream_t ekt,
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unsigned *auth_len,
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void **auth_tag,
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void *tag_copy)
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{
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/*
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* if there is no EKT policy, then the other inputs are unaffected
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*/
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if (!ekt)
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return;
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/* copy auth_tag into temporary location */
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}
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