1 /* 2 * ekt.h 3 * 4 * interface to Encrypted Key Transport for SRTP 5 * 6 * David McGrew 7 * Cisco Systems, Inc. 8 */ 9 /* 10 * 11 * Copyright (c) 2001-2005 Cisco Systems, Inc. 12 * All rights reserved. 13 * 14 * Redistribution and use in source and binary forms, with or without 15 * modification, are permitted provided that the following conditions 16 * are met: 17 * 18 * Redistributions of source code must retain the above copyright 19 * notice, this list of conditions and the following disclaimer. 20 * 21 * Redistributions in binary form must reproduce the above 22 * copyright notice, this list of conditions and the following 23 * disclaimer in the documentation and/or other materials provided 24 * with the distribution. 25 * 26 * Neither the name of the Cisco Systems, Inc. nor the names of its 27 * contributors may be used to endorse or promote products derived 28 * from this software without specific prior written permission. 29 * 30 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 31 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 32 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 33 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 34 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 35 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 36 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 37 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 41 * OF THE POSSIBILITY OF SUCH DAMAGE. 42 * 43 */ 44 45 46 47 /* 48 * EKT implementation strategy 49 * 50 * use stream_template approach 51 * 52 * in srtp_unprotect, when a new stream appears, check if template has 53 * EKT defined, and if it does, then apply EKT processing 54 * 55 * question: will we want to allow key-sharing templates in addition 56 * to EKT templates? could define a new ssrc_type_t that's associated 57 * with an EKT, e.g. ssrc_any_ekt. 58 * 59 * 60 */ 61 62 #ifndef EKT_H 63 #define EKT_H 64 65 #ifdef __cplusplus 66 extern "C" { 67 #endif 68 69 #include "srtp_priv.h" 70 71 #define EKT_CIPHER_DEFAULT 1 72 #define EKT_CIPHER_AES_128_ECB 1 73 #define EKT_CIPHER_AES_192_KEY_WRAP 2 74 #define EKT_CIPHER_AES_256_KEY_WRAP 3 75 76 typedef uint16_t ekt_spi_t; 77 78 79 unsigned 80 ekt_octets_after_base_tag(ekt_stream_t ekt); 81 82 /* 83 * an srtp_policy_t structure can contain a pointer to an 84 * ekt_policy_t structure 85 * 86 * this structure holds all of the high level EKT information, and it 87 * is passed into libsrtp to indicate what policy should be in effect 88 */ 89 90 typedef struct ekt_policy_ctx_t { 91 ekt_spi_t spi; /* security parameter index */ 92 uint8_t ekt_cipher_type; 93 uint8_t *ekt_key; 94 struct ekt_policy_ctx_t *next_ekt_policy; 95 } ekt_policy_ctx_t; 96 97 98 /* 99 * an ekt_data_t structure holds the data corresponding to an ekt key, 100 * spi, and so on 101 */ 102 103 typedef struct ekt_data_t { 104 ekt_spi_t spi; 105 uint8_t ekt_cipher_type; 106 aes_expanded_key_t ekt_enc_key; 107 aes_expanded_key_t ekt_dec_key; 108 struct ekt_data_t *next_ekt_data; 109 } ekt_data_t; 110 111 /* 112 * an srtp_stream_ctx_t can contain an ekt_stream_ctx_t 113 * 114 * an ekt_stream_ctx_t structure holds all of the EKT information for 115 * a specific SRTP stream 116 */ 117 118 typedef struct ekt_stream_ctx_t { 119 ekt_data_t *data; 120 uint16_t isn; /* initial sequence number */ 121 uint8_t encrypted_master_key[SRTP_MAX_KEY_LEN]; 122 } ekt_stream_ctx_t; 123 124 125 126 err_status_t 127 ekt_alloc(ekt_stream_t *stream_data, ekt_policy_t policy); 128 129 err_status_t 130 ekt_stream_init(ekt_stream_t e, 131 ekt_spi_t spi, 132 void *ekt_key, 133 unsigned ekt_cipher_type); 134 135 err_status_t 136 ekt_stream_init_from_policy(ekt_stream_t e, ekt_policy_t p); 137 138 139 140 err_status_t 141 srtp_stream_init_from_ekt(srtp_stream_t stream, 142 const void *srtcp_hdr, 143 unsigned pkt_octet_len); 144 145 146 void 147 ekt_write_data(ekt_stream_t ekt, 148 void *base_tag, 149 unsigned base_tag_len, 150 int *packet_len, 151 xtd_seq_num_t pkt_index); 152 153 /* 154 * We handle EKT by performing some additional steps before 155 * authentication (copying the auth tag into a temporary location, 156 * zeroizing the "base tag" field in the packet) 157 * 158 * With EKT, the tag_len parameter is actually the base tag 159 * length 160 */ 161 162 err_status_t 163 ekt_tag_verification_preproces(uint8_t *pkt_tag, 164 uint8_t *pkt_tag_copy, 165 unsigned tag_len); 166 167 err_status_t 168 ekt_tag_verification_postproces(uint8_t *pkt_tag, 169 uint8_t *pkt_tag_copy, 170 unsigned tag_len); 171 172 173 /* 174 * @brief EKT pre-processing for srtcp tag generation 175 * 176 * This function does the pre-processing of the SRTCP authentication 177 * tag format. When EKT is used, it consists of writing the Encrypted 178 * Master Key, the SRTP ROC, the Initial Sequence Number, and SPI 179 * fields. The Base Authentication Tag field is set to the all-zero 180 * value 181 * 182 * When EKT is not used, this function is a no-op. 183 * 184 */ 185 186 err_status_t 187 srtp_stream_srtcp_auth_tag_generation_preprocess(const srtp_stream_t *s, 188 uint8_t *pkt_tag, 189 unsigned pkt_octet_len); 190 191 /* it's not clear that a tag_generation_postprocess function is needed */ 192 193 err_status_t 194 srtcp_auth_tag_generation_postprocess(); 195 196 197 #ifdef __cplusplus 198 } 199 #endif 200 201 #endif /* EKT_H */ 202