| 1 | .rn '' }` |
| 2 | ''' $RCSfile$$Revision$$Date$ |
| 3 | ''' |
| 4 | ''' $Log$ |
| 5 | ''' |
| 6 | .de Sh |
| 7 | .br |
| 8 | .if t .Sp |
| 9 | .ne 5 |
| 10 | .PP |
| 11 | \fB\\$1\fR |
| 12 | .PP |
| 13 | .. |
| 14 | .de Sp |
| 15 | .if t .sp .5v |
| 16 | .if n .sp |
| 17 | .. |
| 18 | .de Ip |
| 19 | .br |
| 20 | .ie \\n(.$>=3 .ne \\$3 |
| 21 | .el .ne 3 |
| 22 | .IP "\\$1" \\$2 |
| 23 | .. |
| 24 | .de Vb |
| 25 | .ft CW |
| 26 | .nf |
| 27 | .ne \\$1 |
| 28 | .. |
| 29 | .de Ve |
| 30 | .ft R |
| 31 | |
| 32 | .fi |
| 33 | .. |
| 34 | ''' |
| 35 | ''' |
| 36 | ''' Set up \*(-- to give an unbreakable dash; |
| 37 | ''' string Tr holds user defined translation string. |
| 38 | ''' Bell System Logo is used as a dummy character. |
| 39 | ''' |
| 40 | .tr \(*W-|\(bv\*(Tr |
| 41 | .ie n \{\ |
| 42 | .ds -- \(*W- |
| 43 | .ds PI pi |
| 44 | .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch |
| 45 | .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch |
| 46 | .ds L" "" |
| 47 | .ds R" "" |
| 48 | ''' \*(M", \*(S", \*(N" and \*(T" are the equivalent of |
| 49 | ''' \*(L" and \*(R", except that they are used on ".xx" lines, |
| 50 | ''' such as .IP and .SH, which do another additional levels of |
| 51 | ''' double-quote interpretation |
| 52 | .ds M" """ |
| 53 | .ds S" """ |
| 54 | .ds N" """"" |
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| 62 | 'br\} |
| 63 | .el\{\ |
| 64 | .ds -- \(em\| |
| 65 | .tr \*(Tr |
| 66 | .ds L" `` |
| 67 | .ds R" '' |
| 68 | .ds M" `` |
| 69 | .ds S" '' |
| 70 | .ds N" `` |
| 71 | .ds T" '' |
| 72 | .ds L' ` |
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| 74 | .ds M' ` |
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| 76 | .ds N' ` |
| 77 | .ds T' ' |
| 78 | .ds PI \(*p |
| 79 | 'br\} |
| 80 | .\" If the F register is turned on, we'll generate |
| 81 | .\" index entries out stderr for the following things: |
| 82 | .\" TH Title |
| 83 | .\" SH Header |
| 84 | .\" Sh Subsection |
| 85 | .\" Ip Item |
| 86 | .\" X<> Xref (embedded |
| 87 | .\" Of course, you have to process the output yourself |
| 88 | .\" in some meaninful fashion. |
| 89 | .if \nF \{ |
| 90 | .de IX |
| 91 | .tm Index:\\$1\t\\n%\t"\\$2" |
| 92 | .. |
| 93 | .nr % 0 |
| 94 | .rr F |
| 95 | .\} |
| 96 | .TH SSL_CTX_set_tmp_rsa_callback 3 "0.9.7d" "2/Sep/2004" "OpenSSL" |
| 97 | .UC |
| 98 | .if n .hy 0 |
| 99 | .if n .na |
| 100 | .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' |
| 101 | .de CQ \" put $1 in typewriter font |
| 102 | .ft CW |
| 103 | 'if n "\c |
| 104 | 'if t \\&\\$1\c |
| 105 | 'if n \\&\\$1\c |
| 106 | 'if n \&" |
| 107 | \\&\\$2 \\$3 \\$4 \\$5 \\$6 \\$7 |
| 108 | '.ft R |
| 109 | .. |
| 110 | .\" @(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2 |
| 111 | . \" AM - accent mark definitions |
| 112 | .bd B 3 |
| 113 | . \" fudge factors for nroff and troff |
| 114 | .if n \{\ |
| 115 | . ds #H 0 |
| 116 | . ds #V .8m |
| 117 | . ds #F .3m |
| 118 | . ds #[ \f1 |
| 119 | . ds #] \fP |
| 120 | .\} |
| 121 | .if t \{\ |
| 122 | . ds #H ((1u-(\\\\n(.fu%2u))*.13m) |
| 123 | . ds #V .6m |
| 124 | . ds #F 0 |
| 125 | . ds #[ \& |
| 126 | . ds #] \& |
| 127 | .\} |
| 128 | . \" simple accents for nroff and troff |
| 129 | .if n \{\ |
| 130 | . ds ' \& |
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| 132 | . ds ^ \& |
| 133 | . ds , \& |
| 134 | . ds ~ ~ |
| 135 | . ds ? ? |
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| 139 | .\} |
| 140 | .if t \{\ |
| 141 | . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" |
| 142 | . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' |
| 143 | . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' |
| 144 | . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' |
| 145 | . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' |
| 146 | . ds ? \s-2c\h'-\w'c'u*7/10'\u\h'\*(#H'\zi\d\s+2\h'\w'c'u*8/10' |
| 147 | . ds ! \s-2\(or\s+2\h'-\w'\(or'u'\v'-.8m'.\v'.8m' |
| 148 | . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' |
| 149 | . ds q o\h'-\w'o'u*8/10'\s-4\v'.4m'\z\(*i\v'-.4m'\s+4\h'\w'o'u*8/10' |
| 150 | .\} |
| 151 | . \" troff and (daisy-wheel) nroff accents |
| 152 | .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V' |
| 153 | .ds 8 \h'\*(#H'\(*b\h'-\*(#H' |
| 154 | .ds v \\k:\h'-(\\n(.wu*9/10-\*(#H)'\v'-\*(#V'\*(#[\s-4v\s0\v'\*(#V'\h'|\\n:u'\*(#] |
| 155 | .ds _ \\k:\h'-(\\n(.wu*9/10-\*(#H+(\*(#F*2/3))'\v'-.4m'\z\(hy\v'.4m'\h'|\\n:u' |
| 156 | .ds . \\k:\h'-(\\n(.wu*8/10)'\v'\*(#V*4/10'\z.\v'-\*(#V*4/10'\h'|\\n:u' |
| 157 | .ds 3 \*(#[\v'.2m'\s-2\&3\s0\v'-.2m'\*(#] |
| 158 | .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#] |
| 159 | .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H' |
| 160 | .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u' |
| 161 | .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#] |
| 162 | .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#] |
| 163 | .ds ae a\h'-(\w'a'u*4/10)'e |
| 164 | .ds Ae A\h'-(\w'A'u*4/10)'E |
| 165 | .ds oe o\h'-(\w'o'u*4/10)'e |
| 166 | .ds Oe O\h'-(\w'O'u*4/10)'E |
| 167 | . \" corrections for vroff |
| 168 | .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u' |
| 169 | .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u' |
| 170 | . \" for low resolution devices (crt and lpr) |
| 171 | .if \n(.H>23 .if \n(.V>19 \ |
| 172 | \{\ |
| 173 | . ds : e |
| 174 | . ds 8 ss |
| 175 | . ds v \h'-1'\o'\(aa\(ga' |
| 176 | . ds _ \h'-1'^ |
| 177 | . ds . \h'-1'. |
| 178 | . ds 3 3 |
| 179 | . ds o a |
| 180 | . ds d- d\h'-1'\(ga |
| 181 | . ds D- D\h'-1'\(hy |
| 182 | . ds th \o'bp' |
| 183 | . ds Th \o'LP' |
| 184 | . ds ae ae |
| 185 | . ds Ae AE |
| 186 | . ds oe oe |
| 187 | . ds Oe OE |
| 188 | .\} |
| 189 | .rm #[ #] #H #V #F C |
| 190 | .SH "NAME" |
| 191 | SSL_CTX_set_tmp_rsa_callback, SSL_CTX_set_tmp_rsa, SSL_CTX_need_tmp_rsa, SSL_set_tmp_rsa_callback, SSL_set_tmp_rsa, SSL_need_tmp_rsa \- handle RSA keys for ephemeral key exchange |
| 192 | .SH "SYNOPSIS" |
| 193 | .PP |
| 194 | .Vb 1 |
| 195 | \& #include <openssl/ssl.h> |
| 196 | .Ve |
| 197 | .Vb 4 |
| 198 | \& void SSL_CTX_set_tmp_rsa_callback(SSL_CTX *ctx, |
| 199 | \& RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength)); |
| 200 | \& long SSL_CTX_set_tmp_rsa(SSL_CTX *ctx, RSA *rsa); |
| 201 | \& long SSL_CTX_need_tmp_rsa(SSL_CTX *ctx); |
| 202 | .Ve |
| 203 | .Vb 4 |
| 204 | \& void SSL_set_tmp_rsa_callback(SSL_CTX *ctx, |
| 205 | \& RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength)); |
| 206 | \& long SSL_set_tmp_rsa(SSL *ssl, RSA *rsa) |
| 207 | \& long SSL_need_tmp_rsa(SSL *ssl) |
| 208 | .Ve |
| 209 | .Vb 1 |
| 210 | \& RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength)); |
| 211 | .Ve |
| 212 | .SH "DESCRIPTION" |
| 213 | \fISSL_CTX_set_tmp_rsa_callback()\fR sets the callback function for \fBctx\fR to be |
| 214 | used when a temporary/ephemeral RSA key is required to \fBtmp_rsa_callback\fR. |
| 215 | The callback is inherited by all SSL objects newly created from \fBctx\fR |
| 216 | with <\fISSL_new\fR\|(3)|\fISSL_new\fR\|(3)>. Already created SSL objects are not affected. |
| 217 | .PP |
| 218 | \fISSL_CTX_set_tmp_rsa()\fR sets the temporary/ephemeral RSA key to be used to be |
| 219 | \fBrsa\fR. The key is inherited by all SSL objects newly created from \fBctx\fR |
| 220 | with <\fISSL_new\fR\|(3)|\fISSL_new\fR\|(3)>. Already created SSL objects are not affected. |
| 221 | .PP |
| 222 | \fISSL_CTX_need_tmp_rsa()\fR returns 1, if a temporary/ephemeral RSA key is needed |
| 223 | for RSA\-based strength-limited \*(L'exportable\*(R' ciphersuites because a RSA key |
| 224 | with a keysize larger than 512 bits is installed. |
| 225 | .PP |
| 226 | \fISSL_set_tmp_rsa_callback()\fR sets the callback only for \fBssl\fR. |
| 227 | .PP |
| 228 | \fISSL_set_tmp_rsa()\fR sets the key only for \fBssl\fR. |
| 229 | .PP |
| 230 | \fISSL_need_tmp_rsa()\fR returns 1, if a temporary/ephemeral RSA key is needed, |
| 231 | for RSA\-based strength-limited \*(L'exportable\*(R' ciphersuites because a RSA key |
| 232 | with a keysize larger than 512 bits is installed. |
| 233 | .PP |
| 234 | These functions apply to SSL/TLS servers only. |
| 235 | .SH "NOTES" |
| 236 | When using a cipher with RSA authentication, an ephemeral RSA key exchange |
| 237 | can take place. In this case the session data are negotiated using the |
| 238 | ephemeral/temporary RSA key and the RSA key supplied and certified |
| 239 | by the certificate chain is only used for signing. |
| 240 | .PP |
| 241 | Under previous export restrictions, ciphers with RSA keys shorter (512 bits) |
| 242 | than the usual key length of 1024 bits were created. To use these ciphers |
| 243 | with RSA keys of usual length, an ephemeral key exchange must be performed, |
| 244 | as the normal (certified) key cannot be directly used. |
| 245 | .PP |
| 246 | Using ephemeral RSA key exchange yields forward secrecy, as the connection |
| 247 | can only be decrypted, when the RSA key is known. By generating a temporary |
| 248 | RSA key inside the server application that is lost when the application |
| 249 | is left, it becomes impossible for an attacker to decrypt past sessions, |
| 250 | even if he gets hold of the normal (certified) RSA key, as this key was |
| 251 | used for signing only. The downside is that creating a RSA key is |
| 252 | computationally expensive. |
| 253 | .PP |
| 254 | Additionally, the use of ephemeral RSA key exchange is only allowed in |
| 255 | the TLS standard, when the RSA key can be used for signing only, that is |
| 256 | for export ciphers. Using ephemeral RSA key exchange for other purposes |
| 257 | violates the standard and can break interoperability with clients. |
| 258 | It is therefore strongly recommended to not use ephemeral RSA key |
| 259 | exchange and use EDH (Ephemeral Diffie-Hellman) key exchange instead |
| 260 | in order to achieve forward secrecy (see |
| 261 | SSL_CTX_set_tmp_dh_callback(3)). |
| 262 | .PP |
| 263 | On OpenSSL servers ephemeral RSA key exchange is therefore disabled by default |
| 264 | and must be explicitly enabled using the SSL_OP_EPHEMERAL_RSA option of |
| 265 | SSL_CTX_set_options(3), violating the TLS/SSL |
| 266 | standard. When ephemeral RSA key exchange is required for export ciphers, |
| 267 | it will automatically be used without this option! |
| 268 | .PP |
| 269 | An application may either directly specify the key or can supply the key via |
| 270 | a callback function. The callback approach has the advantage, that the |
| 271 | callback may generate the key only in case it is actually needed. As the |
| 272 | generation of a RSA key is however costly, it will lead to a significant |
| 273 | delay in the handshake procedure. Another advantage of the callback function |
| 274 | is that it can supply keys of different size (e.g. for SSL_OP_EPHEMERAL_RSA |
| 275 | usage) while the explicit setting of the key is only useful for key size of |
| 276 | 512 bits to satisfy the export restricted ciphers and does give away key length |
| 277 | if a longer key would be allowed. |
| 278 | .PP |
| 279 | The \fBtmp_rsa_callback\fR is called with the \fBkeylength\fR needed and |
| 280 | the \fBis_export\fR information. The \fBis_export\fR flag is set, when the |
| 281 | ephemeral RSA key exchange is performed with an export cipher. |
| 282 | .SH "EXAMPLES" |
| 283 | Generate temporary RSA keys to prepare ephemeral RSA key exchange. As the |
| 284 | generation of a RSA key costs a lot of computer time, they saved for later |
| 285 | reuse. For demonstration purposes, two keys for 512 bits and 1024 bits |
| 286 | respectively are generated. |
| 287 | .PP |
| 288 | .Vb 4 |
| 289 | \& ... |
| 290 | \& /* Set up ephemeral RSA stuff */ |
| 291 | \& RSA *rsa_512 = NULL; |
| 292 | \& RSA *rsa_1024 = NULL; |
| 293 | .Ve |
| 294 | .Vb 3 |
| 295 | \& rsa_512 = RSA_generate_key(512,RSA_F4,NULL,NULL); |
| 296 | \& if (rsa_512 == NULL) |
| 297 | \& evaluate_error_queue(); |
| 298 | .Ve |
| 299 | .Vb 3 |
| 300 | \& rsa_1024 = RSA_generate_key(1024,RSA_F4,NULL,NULL); |
| 301 | \& if (rsa_1024 == NULL) |
| 302 | \& evaluate_error_queue(); |
| 303 | .Ve |
| 304 | .Vb 1 |
| 305 | \& ... |
| 306 | .Ve |
| 307 | .Vb 3 |
| 308 | \& RSA *tmp_rsa_callback(SSL *s, int is_export, int keylength) |
| 309 | \& { |
| 310 | \& RSA *rsa_tmp=NULL; |
| 311 | .Ve |
| 312 | .Vb 24 |
| 313 | \& switch (keylength) { |
| 314 | \& case 512: |
| 315 | \& if (rsa_512) |
| 316 | \& rsa_tmp = rsa_512; |
| 317 | \& else { /* generate on the fly, should not happen in this example */ |
| 318 | \& rsa_tmp = RSA_generate_key(keylength,RSA_F4,NULL,NULL); |
| 319 | \& rsa_512 = rsa_tmp; /* Remember for later reuse */ |
| 320 | \& } |
| 321 | \& break; |
| 322 | \& case 1024: |
| 323 | \& if (rsa_1024) |
| 324 | \& rsa_tmp=rsa_1024; |
| 325 | \& else |
| 326 | \& should_not_happen_in_this_example(); |
| 327 | \& break; |
| 328 | \& default: |
| 329 | \& /* Generating a key on the fly is very costly, so use what is there */ |
| 330 | \& if (rsa_1024) |
| 331 | \& rsa_tmp=rsa_1024; |
| 332 | \& else |
| 333 | \& rsa_tmp=rsa_512; /* Use at least a shorter key */ |
| 334 | \& } |
| 335 | \& return(rsa_tmp); |
| 336 | \& } |
| 337 | .Ve |
| 338 | .SH "RETURN VALUES" |
| 339 | \fISSL_CTX_set_tmp_rsa_callback()\fR and \fISSL_set_tmp_rsa_callback()\fR do not return |
| 340 | diagnostic output. |
| 341 | .PP |
| 342 | \fISSL_CTX_set_tmp_rsa()\fR and \fISSL_set_tmp_rsa()\fR do return 1 on success and 0 |
| 343 | on failure. Check the error queue to find out the reason of failure. |
| 344 | .PP |
| 345 | \fISSL_CTX_need_tmp_rsa()\fR and \fISSL_need_tmp_rsa()\fR return 1 if a temporary |
| 346 | RSA key is needed and 0 otherwise. |
| 347 | .SH "SEE ALSO" |
| 348 | ssl(3), SSL_CTX_set_cipher_list(3), |
| 349 | SSL_CTX_set_options(3), |
| 350 | SSL_CTX_set_tmp_dh_callback(3), |
| 351 | SSL_new(3), ciphers(1) |
| 352 | |
| 353 | .rn }` '' |
| 354 | .IX Title "SSL_CTX_set_tmp_rsa_callback 3" |
| 355 | .IX Name "SSL_CTX_set_tmp_rsa_callback, SSL_CTX_set_tmp_rsa, SSL_CTX_need_tmp_rsa, SSL_set_tmp_rsa_callback, SSL_set_tmp_rsa, SSL_need_tmp_rsa - handle RSA keys for ephemeral key exchange" |
| 356 | |
| 357 | .IX Header "NAME" |
| 358 | |
| 359 | .IX Header "SYNOPSIS" |
| 360 | |
| 361 | .IX Header "DESCRIPTION" |
| 362 | |
| 363 | .IX Header "NOTES" |
| 364 | |
| 365 | .IX Header "EXAMPLES" |
| 366 | |
| 367 | .IX Header "RETURN VALUES" |
| 368 | |
| 369 | .IX Header "SEE ALSO" |
| 370 | |