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Diffstat (limited to 'secure/lib/libcrypto/man/SSL_CTX_set_tmp_rsa_callback.3')
| -rw-r--r-- | secure/lib/libcrypto/man/SSL_CTX_set_tmp_rsa_callback.3 | 309 |
1 files changed, 309 insertions, 0 deletions
diff --git a/secure/lib/libcrypto/man/SSL_CTX_set_tmp_rsa_callback.3 b/secure/lib/libcrypto/man/SSL_CTX_set_tmp_rsa_callback.3 new file mode 100644 index 000000000000..655f4882b9c1 --- /dev/null +++ b/secure/lib/libcrypto/man/SSL_CTX_set_tmp_rsa_callback.3 @@ -0,0 +1,309 @@ +.\" Automatically generated by Pod::Man version 1.15 +.\" Thu May 9 13:22:26 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. 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Already created \s-1SSL\s0 objects are not affected. +.PP +\&\fISSL_CTX_set_tmp_rsa()\fR sets the temporary/ephemeral \s-1RSA\s0 key to be used to be +\&\fBrsa\fR. The key is inherited by all \s-1SSL\s0 objects newly created from \fBctx\fR +with <\fISSL_new\fR\|(3)|\fISSL_new\fR\|(3)>. Already created \s-1SSL\s0 objects are not affected. +.PP +\&\fISSL_CTX_need_tmp_rsa()\fR returns 1, if a temporary/ephemeral \s-1RSA\s0 key is needed +for RSA-based strength-limited 'exportable' ciphersuites because a \s-1RSA\s0 key +with a keysize larger than 512 bits is installed. +.PP +\&\fISSL_set_tmp_rsa_callback()\fR sets the callback only for \fBssl\fR. +.PP +\&\fISSL_set_tmp_rsa()\fR sets the key only for \fBssl\fR. +.PP +\&\fISSL_need_tmp_rsa()\fR returns 1, if a temporary/ephemeral \s-1RSA\s0 key is needed, +for RSA-based strength-limited 'exportable' ciphersuites because a \s-1RSA\s0 key +with a keysize larger than 512 bits is installed. +.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-1RSA\s0 key exchange +can take place. In this case the session data are negotiated using the +ephemeral/temporary \s-1RSA\s0 key and the \s-1RSA\s0 key supplied and certified +by the certificate chain is only used for signing. +.PP +Under previous export restrictions, ciphers with \s-1RSA\s0 keys shorter (512 bits) +than the usual key length of 1024 bits were created. To use these ciphers +with \s-1RSA\s0 keys of usual length, an ephemeral key exchange must be performed, +as the normal (certified) key cannot be directly used. +.PP +Using ephemeral \s-1RSA\s0 key exchange yields forward secrecy, as the connection +can only be decrypted, when the \s-1RSA\s0 key is known. By generating a temporary +\&\s-1RSA\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) \s-1RSA\s0 key, as this key was +used for signing only. The downside is that creating a \s-1RSA\s0 key is +computationally expensive. +.PP +Additionally, the use of ephemeral \s-1RSA\s0 key exchange is only allowed in +the \s-1TLS\s0 standard, when the \s-1RSA\s0 key can be used for signing only, that is +for export ciphers. Using ephemeral \s-1RSA\s0 key exchange for other purposes +violates the standard and can break interoperability with clients. +It is therefore strongly recommended to not use ephemeral \s-1RSA\s0 key +exchange and use \s-1EDH\s0 (Ephemeral Diffie-Hellman) key exchange instead +in order to achieve forward secrecy (see +SSL_CTX_set_tmp_dh_callback(3)). +.PP +On OpenSSL servers ephemeral \s-1RSA\s0 key exchange is therefore disabled by default +and must be explicitly enabled using the \s-1SSL_OP_EPHEMERAL_RSA\s0 option of +SSL_CTX_set_options(3), violating the \s-1TLS/SSL\s0 +standard. When ephemeral \s-1RSA\s0 key exchange is required for export ciphers, +it will automatically be used without this option! +.PP +An application may either directly specify the key or can supply the key via +a callback function. The callback approach has the advantage, that the +callback may generate the key only in case it is actually needed. As the +generation of a \s-1RSA\s0 key is however costly, it will lead to a significant +delay in the handshake procedure. Another advantage of the callback function +is that it can supply keys of different size (e.g. for \s-1SSL_OP_EPHEMERAL_RSA\s0 +usage) while the explicit setting of the key is only useful for key size of +512 bits to satisfy the export restricted ciphers and does give away key length +if a longer key would be allowed. +.PP +The \fBtmp_rsa_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-1RSA\s0 key exchange is performed with an export cipher. +.SH "EXAMPLES" +.IX Header "EXAMPLES" +Generate temporary \s-1RSA\s0 keys to prepare ephemeral \s-1RSA\s0 key exchange. As the +generation of a \s-1RSA\s0 key costs a lot of computer time, they saved for later +reuse. For demonstration purposes, two keys for 512 bits and 1024 bits +respectively are generated. +.PP +.Vb 4 +\& ... +\& /* Set up ephemeral RSA stuff */ +\& RSA *rsa_512 = NULL; +\& RSA *rsa_1024 = NULL; +.Ve +.Vb 3 +\& rsa_512 = RSA_generate_key(512,RSA_F4,NULL,NULL); +\& if (rsa_512 == NULL) +\& evaluate_error_queue(); +.Ve +.Vb 3 +\& rsa_1024 = RSA_generate_key(1024,RSA_F4,NULL,NULL); +\& if (rsa_1024 == NULL) +\& evaluate_error_queue(); +.Ve +.Vb 1 +\& ... +.Ve +.Vb 3 +\& RSA *tmp_rsa_callback(SSL *s, int is_export, int keylength) +\& { +\& RSA *rsa_tmp=NULL; +.Ve +.Vb 24 +\& switch (keylength) { +\& case 512: +\& if (rsa_512) +\& rsa_tmp = rsa_512; +\& else { /* generate on the fly, should not happen in this example */ +\& rsa_tmp = RSA_generate_key(keylength,RSA_F4,NULL,NULL); +\& rsa_512 = rsa_tmp; /* Remember for later reuse */ +\& } +\& break; +\& case 1024: +\& if (rsa_1024) +\& rsa_tmp=rsa_1024; +\& else +\& should_not_happen_in_this_example(); +\& break; +\& default: +\& /* Generating a key on the fly is very costly, so use what is there */ +\& if (rsa_1024) +\& rsa_tmp=rsa_1024; +\& else +\& rsa_tmp=rsa_512; /* Use at least a shorter key */ +\& } +\& return(rsa_tmp); +\& } +.Ve +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +\&\fISSL_CTX_set_tmp_rsa_callback()\fR and \fISSL_set_tmp_rsa_callback()\fR do not return +diagnostic output. +.PP +\&\fISSL_CTX_set_tmp_rsa()\fR and \fISSL_set_tmp_rsa()\fR do return 1 on success and 0 +on failure. Check the error queue to find out the reason of failure. +.PP +\&\fISSL_CTX_need_tmp_rsa()\fR and \fISSL_need_tmp_rsa()\fR return 1 if a temporary +\&\s-1RSA\s0 key is needed and 0 otherwise. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +ssl(3), SSL_CTX_set_cipher_list(3), +SSL_CTX_set_options(3), +SSL_CTX_set_tmp_dh_callback(3), +SSL_new(3), ciphers(1) |