diff options
Diffstat (limited to 'secure/lib/libcrypto/man/SSL_CTX_set_tmp_dh_callback.3')
| -rw-r--r-- | secure/lib/libcrypto/man/SSL_CTX_set_tmp_dh_callback.3 | 312 |
1 files changed, 312 insertions, 0 deletions
diff --git a/secure/lib/libcrypto/man/SSL_CTX_set_tmp_dh_callback.3 b/secure/lib/libcrypto/man/SSL_CTX_set_tmp_dh_callback.3 new file mode 100644 index 0000000..5c9d0e7 --- /dev/null +++ b/secure/lib/libcrypto/man/SSL_CTX_set_tmp_dh_callback.3 @@ -0,0 +1,312 @@ +.\" Automatically generated by Pod::Man version 1.15 +.\" Thu May 9 13:22:24 2002 +.\" +.\" Standard preamble: +.\" ====================================================================== +.de Sh \" Subsection heading +.br +.if t .Sp +.ne 5 +.PP +\fB\\$1\fR +.PP +.. +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Ip \" List item +.br +.ie \\n(.$>=3 .ne \\$3 +.el .ne 3 +.IP "\\$1" \\$2 +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R + +.fi +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. | will give a +.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used +.\" to do unbreakable dashes and therefore won't be available. \*(C` and +.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<> +.tr \(*W-|\(bv\*(Tr +.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' +.ie n \{\ +. ds -- \(*W- +. ds PI pi +. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch +. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch +. ds L" "" +. ds R" "" +. ds C` "" +. ds C' "" +'br\} +.el\{\ +. ds -- \|\(em\| +. ds PI \(*p +. ds L" `` +. ds R" '' +'br\} +.\" +.\" If the F register is turned on, we'll generate index entries on stderr +.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and +.\" index entries marked with X<> in POD. Of course, you'll have to process +.\" the output yourself in some meaningful fashion. +.if \nF \{\ +. de IX +. tm Index:\\$1\t\\n%\t"\\$2" +.. +. nr % 0 +. rr F +.\} +.\" +.\" For nroff, turn off justification. Always turn off hyphenation; it +.\" makes way too many mistakes in technical documents. +.hy 0 +.if n .na +.\" +.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). +.\" Fear. Run. Save yourself. No user-serviceable parts. +.bd B 3 +. \" fudge factors for nroff and troff +.if n \{\ +. ds #H 0 +. ds #V .8m +. ds #F .3m +. ds #[ \f1 +. ds #] \fP +.\} +.if t \{\ +. ds #H ((1u-(\\\\n(.fu%2u))*.13m) +. ds #V .6m +. ds #F 0 +. ds #[ \& +. ds #] \& +.\} +. \" simple accents for nroff and troff +.if n \{\ +. ds ' \& +. ds ` \& +. ds ^ \& +. ds , \& +. ds ~ ~ +. ds / +.\} +.if t \{\ +. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" +. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' +. ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' +. ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' +. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' +. ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' +.\} +. \" troff and (daisy-wheel) nroff accents +.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V' +.ds 8 \h'\*(#H'\(*b\h'-\*(#H' +.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#] +.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H' +.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u' +.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#] +.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#] +.ds ae a\h'-(\w'a'u*4/10)'e +.ds Ae A\h'-(\w'A'u*4/10)'E +. \" corrections for vroff +.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u' +.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u' +. \" for low resolution devices (crt and lpr) +.if \n(.H>23 .if \n(.V>19 \ +\{\ +. ds : e +. ds 8 ss +. ds o a +. ds d- d\h'-1'\(ga +. ds D- D\h'-1'\(hy +. ds th \o'bp' +. ds Th \o'LP' +. ds ae ae +. ds Ae AE +.\} +.rm #[ #] #H #V #F C +.\" ====================================================================== +.\" +.IX Title "SSL_CTX_SET_TMP_DH_CALLBACK 1" +.TH SSL_CTX_SET_TMP_DH_CALLBACK 1 "perl v5.6.1" "2002-01-27" "User Contributed Perl Documentation" +.UC +.SH "NAME" +SSL_CTX_set_tmp_dh_callback, SSL_CTX_set_tmp_dh, SSL_set_tmp_dh_callback, SSL_set_tmp_dh \- handle \s-1DH\s0 keys for ephemeral key exchange +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/ssl.h> +.Ve +.Vb 3 +\& void SSL_CTX_set_tmp_dh_callback(SSL_CTX *ctx, +\& DH *(*tmp_dh_callback)(SSL *ssl, int is_export, int keylength)); +\& long SSL_CTX_set_tmp_dh(SSL_CTX *ctx, DH *dh); +.Ve +.Vb 3 +\& void SSL_set_tmp_dh_callback(SSL_CTX *ctx, +\& DH *(*tmp_dh_callback)(SSL *ssl, int is_export, int keylength)); +\& long SSL_set_tmp_dh(SSL *ssl, DH *dh) +.Ve +.Vb 1 +\& DH *(*tmp_dh_callback)(SSL *ssl, int is_export, int keylength)); +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +\&\fISSL_CTX_set_tmp_dh_callback()\fR sets the callback function for \fBctx\fR to be +used when a \s-1DH\s0 parameters are required to \fBtmp_dh_callback\fR. +The callback is inherited by all \fBssl\fR objects created from \fBctx\fR. +.PP +\&\fISSL_CTX_set_tmp_dh()\fR sets \s-1DH\s0 parameters to be used to be \fBdh\fR. +The key is inherited by all \fBssl\fR objects created from \fBctx\fR. +.PP +\&\fISSL_set_tmp_dh_callback()\fR sets the callback only for \fBssl\fR. +.PP +\&\fISSL_set_tmp_dh()\fR sets the parameters only for \fBssl\fR. +.PP +These functions apply to \s-1SSL/TLS\s0 servers only. +.SH "NOTES" +.IX Header "NOTES" +When using a cipher with \s-1RSA\s0 authentication, an ephemeral \s-1DH\s0 key exchange +can take place. Ciphers with \s-1DSA\s0 keys always use ephemeral \s-1DH\s0 keys as well. +In these cases, the session data are negotiated using the +ephemeral/temporary \s-1DH\s0 key and the key supplied and certified +by the certificate chain is only used for signing. +Anonymous ciphers (without a permanent server key) also use ephemeral \s-1DH\s0 keys. +.PP +Using ephemeral \s-1DH\s0 key exchange yields forward secrecy, as the connection +can only be decrypted, when the \s-1DH\s0 key is known. By generating a temporary +\&\s-1DH\s0 key inside the server application that is lost when the application +is left, it becomes impossible for an attacker to decrypt past sessions, +even if he gets hold of the normal (certified) key, as this key was +only used for signing. +.PP +In order to perform a \s-1DH\s0 key exchange the server must use a \s-1DH\s0 group +(\s-1DH\s0 parameters) and generate a \s-1DH\s0 key. The server will always generate a new +\&\s-1DH\s0 key during the negotiation, when the \s-1DH\s0 parameters are supplied via +callback and/or when the \s-1SSL_OP_SINGLE_DH_USE\s0 option of +SSL_CTX_set_options(3) is set. It will +immediately create a \s-1DH\s0 key, when \s-1DH\s0 parameters are supplied via +\&\fISSL_CTX_set_tmp_dh()\fR and \s-1SSL_OP_SINGLE_DH_USE\s0 is not set. In this case, +it may happen that a key is generated on initialization without later +being needed, while on the other hand the computer time during the +negotiation is being saved. +.PP +If \*(L"strong\*(R" primes were used to generate the \s-1DH\s0 parameters, it is not strictly +necessary to generate a new key for each handshake but it does improve forward +secrecy. If it is not assured, that \*(L"strong\*(R" primes were used (see especially +the section about \s-1DSA\s0 parameters below), \s-1SSL_OP_SINGLE_DH_USE\s0 must be used +in order to prevent small subgroup attacks. Always using \s-1SSL_OP_SINGLE_DH_USE\s0 +has an impact on the computer time needed during negotiation, but it is not +very large, so application authors/users should consider to always enable +this option. +.PP +As generating \s-1DH\s0 parameters is extremely time consuming, an application +should not generate the parameters on the fly but supply the parameters. +\&\s-1DH\s0 parameters can be reused, as the actual key is newly generated during +the negotiation. The risk in reusing \s-1DH\s0 parameters is that an attacker +may specialize on a very often used \s-1DH\s0 group. Applications should therefore +generate their own \s-1DH\s0 parameters during the installation process using the +openssl dhparam(1) application. In order to reduce the computer +time needed for this generation, it is possible to use \s-1DSA\s0 parameters +instead (see dhparam(1)), but in this case \s-1SSL_OP_SINGLE_DH_USE\s0 +is mandatory. +.PP +Application authors may compile in \s-1DH\s0 parameters. Files dh512.pem, +dh1024.pem, dh2048.pem, and dh4096 in the 'apps' directory of current +version of the OpenSSL distribution contain the '\s-1SKIP\s0' \s-1DH\s0 parameters, +which use safe primes and were generated verifiably pseudo-randomly. +These files can be converted into C code using the \fB\-C\fR option of the +dhparam(1) application. +Authors may also generate their own set of parameters using +dhparam(1), but a user may not be sure how the parameters were +generated. The generation of \s-1DH\s0 parameters during installation is therefore +recommended. +.PP +An application may either directly specify the \s-1DH\s0 parameters or +can supply the \s-1DH\s0 parameters via a callback function. The callback approach +has the advantage, that the callback may supply \s-1DH\s0 parameters for different +key lengths. +.PP +The \fBtmp_dh_callback\fR is called with the \fBkeylength\fR needed and +the \fBis_export\fR information. The \fBis_export\fR flag is set, when the +ephemeral \s-1DH\s0 key exchange is performed with an export cipher. +.SH "EXAMPLES" +.IX Header "EXAMPLES" +Handle \s-1DH\s0 parameters for key lengths of 512 and 1024 bits. (Error handling +partly left out.) +.PP +.Vb 5 +\& ... +\& /* Set up ephemeral DH stuff */ +\& DH *dh_512 = NULL; +\& DH *dh_1024 = NULL; +\& FILE *paramfile; +.Ve +.Vb 14 +\& ... +\& /* "openssl dhparam -out dh_param_512.pem -2 512" */ +\& paramfile = fopen("dh_param_512.pem", "r"); +\& if (paramfile) { +\& dh_512 = PEM_read_DHparams(paramfile, NULL, NULL, NULL); +\& fclose(paramfile); +\& } +\& /* "openssl dhparam -out dh_param_1024.pem -2 1024" */ +\& paramfile = fopen("dh_param_1024.pem", "r"); +\& if (paramfile) { +\& dh_1024 = PEM_read_DHparams(paramfile, NULL, NULL, NULL); +\& fclose(paramfile); +\& } +\& ... +.Ve +.Vb 3 +\& /* "openssl dhparam -C -2 512" etc... */ +\& DH *get_dh512() { ... } +\& DH *get_dh1024() { ... } +.Ve +.Vb 3 +\& DH *tmp_dh_callback(SSL *s, int is_export, int keylength) +\& { +\& DH *dh_tmp=NULL; +.Ve +.Vb 17 +\& switch (keylength) { +\& case 512: +\& if (!dh_512) +\& dh_512 = get_dh512(); +\& dh_tmp = dh_512; +\& break; +\& case 1024: +\& if (!dh_1024) +\& dh_1024 = get_dh1024(); +\& dh_tmp = dh_1024; +\& break; +\& default: +\& /* Generating a key on the fly is very costly, so use what is there */ +\& setup_dh_parameters_like_above(); +\& } +\& return(dh_tmp); +\& } +.Ve +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +\&\fISSL_CTX_set_tmp_dh_callback()\fR and \fISSL_set_tmp_dh_callback()\fR do not return +diagnostic output. +.PP +\&\fISSL_CTX_set_tmp_dh()\fR and \fISSL_set_tmp_dh()\fR do return 1 on success and 0 +on failure. Check the error queue to find out the reason of failure. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +ssl(3), SSL_CTX_set_cipher_list(3), +SSL_CTX_set_tmp_rsa_callback(3), +SSL_CTX_set_options(3), +ciphers(1), dhparam(1) |
