1Secure RTP (SRTP) Reference Implementation 2David A. McGrew 3Cisco Systems, Inc. 4mcgrew@cisco.com 5 6 7This package provides an implementation of the Secure Real-time 8Transport Protocol (SRTP), the Universal Security Transform (UST), and 9a supporting cryptographic kernel. These mechanisms are documented in 10the Internet Drafts in the doc/ subdirectory. The SRTP API is 11documented in include/srtp.h, and the library is in libsrtp.a (after 12compilation). An overview and reference manual is available in 13doc/libsrtp.pdf. The PDF documentation is more up to date than this 14file. 15 16 17Installation: 18 19./configure [ options ] # GNU autoconf script 20make # or gmake if needed; use GNU make 21 22The configure script accepts the following options: 23 24 --help provides a usage summary 25 --disable-debug compile without the runtime debugging system 26 --enable-syslog use syslog for error reporting 27 --disable-stdout use stdout for error reporting 28 --enable-console use /dev/console for error reporting 29 --gdoi use GDOI key management (disabled at present) 30 31By default, debbuging is enabled and stdout is used for debugging. 32You can use the above configure options to have the debugging output 33sent to syslog or the system console. Alternatively, you can define 34ERR_REPORTING_FILE in include/conf.h to be any other file that can be 35opened by libSRTP, and debug messages will be sent to it. 36 37This package has been tested on Mac OS X (powerpc-apple-darwin1.4), 38Cygwin (i686-pc-cygwin), and Sparc (sparc-sun-solaris2.6). Previous 39versions have been tested on Linux and OpenBSD on both x86 and sparc 40platforms. 41 42A quick tour of this package: 43 44Makefile targets: all, clean, ... 45README this file 46CHANGES change log 47VERSION version number of this package 48LICENSE legal details (it's a BSD-like license) 49crypto/ciphers/ ciphers (null, aes_icm, ...) 50crypto/math/ crypto math routines 51crypto/hash/ crypto hashing (hmac, tmmhv2, ...) 52crypto/replay/ replay protection 53doc/ documentation: rfcs, apis, and suchlike 54include/ include files for all code in distribution 55srtp/ secure real-time transport protocol implementation 56tables/ apps for generating tables (useful in porting) 57test/ test drivers 58 59 60Applications 61 62 Several test drivers and a simple and portable srtp application 63 are included in the test/ subdirectory. 64 65 test driver function tested 66 ------------------------------------------------------------- 67 kernel_driver crypto kernel (ciphers, auth funcs, rng) 68 srtp_driver srtp in-memory tests (does not use the network) 69 rdbx_driver rdbx (extended replay database) 70 roc_driver extended sequence number functions 71 replay_driver replay database (n.b. not used in libsrtp) 72 cipher_driver ciphers 73 auth_driver hash functions 74 75 The app rtpw is a simple rtp application which reads words from 76 /usr/dict/words and then sends them out one at a time using [s]rtp. 77 Manual srtp keying uses the -k option; automated key management 78 using gdoi will be added later. 79 80usage: rtpw [-d <debug>]* [-k <key> [-a][-e]] [-s | -r] dest_ip dest_port 81or rtpw -l 82 83 Either the -s (sender) or -r (receiver) option must be chosen. 84 85 The values dest_ip, dest_port are the ip address and udp port to 86 which the dictionary will be sent, respectively. 87 88 options: 89 90 -s (s)rtp sender - causes app to send words 91 92 -r (s)rtp receive - causes app to receve words 93 94 -k <key> use srtp master key <key>, where the 95 key is a hexadecimal value (without the 96 leading "0x") 97 98 -e encrypt/decrypt (for data confidentiality) 99 (requires use of -k option as well) 100 101 -a message authentication 102 (requires use of -k option as well) 103 104 -l list debug modules 105 106 -d <debug> turn on debugging for module <debug> 107 108 109In order to get random 30-byte values for use as key/salt pairs , you 110can use the following bash function to format the output of 111/dev/random (where that device is available). 112 113function randhex() { 114 cat /dev/random | od --read-bytes=32 --width=32 -x | awk '{ print $2 $3 $4 $5 $6 $7 $8 $9 $10 $11 $12 $13 $14 $15 $16 }' 115} 116 117 118An example of an SRTP session using two rtpw programs follows: 119 120set k=c1eec3717da76195bb878578790af71c4ee9f859e197a414a78d5abc7451 121 122[sh1]$ test/rtpw -s -k $k -ea 0.0.0.0 9999 123Security services: confidentiality message authentication 124set master key/salt to C1EEC3717DA76195BB878578790AF71C/4EE9F859E197A414A78D5ABC7451 125setting SSRC to 2078917053 126sending word: A 127sending word: a 128sending word: aa 129sending word: aal 130... 131 132[sh2]$ test/rtpw -r -k $k -ea 0.0.0.0 9999 133security services: confidentiality message authentication 134set master key/salt to C1EEC3717DA76195BB878578790AF71C/4EE9F859E197A414A78D5ABC7451 13519 octets received from SSRC 2078917053 word: A 13619 octets received from SSRC 2078917053 word: a 13720 octets received from SSRC 2078917053 word: aa 13821 octets received from SSRC 2078917053 word: aal 139... 140 141Implementation Notes 142 143 * The srtp_protect() function assumes that the buffer holding the 144 rtp packet has enough storage allocated that the authentication 145 tag can be written to the end of that packet. If this assumption 146 is not valid, memory corruption will ensue. 147 148 * Automated tests for the crypto functions are provided through 149 the cipher_type_self_test() and auth_type_self_test() functions. 150 These functions should be used to test each port of this code 151 to a new platform. 152 153 * Replay protection is contained in the crypto engine, and 154 tests for it are provided. 155 156 * This implementation provides calls to initialize, protect, and 157 unprotect RTP packets, and makes as few as possible assumptions 158 about how these functions will be called. For example, the 159 caller is not expected to provide packets in order (though if 160 they're called more than 65k out of sequence, synchronization 161 will be lost). 162 163 * The sequence number in the rtp packet is used as the low 16 bits 164 of the sender's local packet index. Note that RTP will start its 165 sequence number in a random place, and the SRTP layer just jumps 166 forward to that number at its first invocation. An earlier 167 version of this library used initial sequence numbers that are 168 less than 32,768; this trick is no longer required as the 169 rdbx_estimate_index(...) function has been made smarter. 170 171 * The replay window is 128 bits in length, and is hard-coded to this 172 value for now. 173 174 175