+++ /dev/null
-=pod
-
-=head1 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
-
-=head1 SYNOPSIS
-
- #include <openssl/ssl.h>
-
- void SSL_CTX_set_tmp_rsa_callback(SSL_CTX *ctx,
- RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength));
- long SSL_CTX_set_tmp_rsa(SSL_CTX *ctx, RSA *rsa);
- long SSL_CTX_need_tmp_rsa(SSL_CTX *ctx);
-
- void SSL_set_tmp_rsa_callback(SSL_CTX *ctx,
- RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength));
- long SSL_set_tmp_rsa(SSL *ssl, RSA *rsa)
- long SSL_need_tmp_rsa(SSL *ssl)
-
- RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength);
-
-=head1 DESCRIPTION
-
-SSL_CTX_set_tmp_rsa_callback() sets the callback function for B<ctx> to be
-used when a temporary/ephemeral RSA key is required to B<tmp_rsa_callback>.
-The callback is inherited by all SSL objects newly created from B<ctx>
-with <SSL_new(3)|SSL_new(3)>. Already created SSL objects are not affected.
-
-SSL_CTX_set_tmp_rsa() sets the temporary/ephemeral RSA key to be used to be
-B<rsa>. The key is inherited by all SSL objects newly created from B<ctx>
-with <SSL_new(3)|SSL_new(3)>. Already created SSL objects are not affected.
-
-SSL_CTX_need_tmp_rsa() returns 1, if a temporary/ephemeral RSA key is needed
-for RSA-based strength-limited 'exportable' ciphersuites because a RSA key
-with a keysize larger than 512 bits is installed.
-
-SSL_set_tmp_rsa_callback() sets the callback only for B<ssl>.
-
-SSL_set_tmp_rsa() sets the key only for B<ssl>.
-
-SSL_need_tmp_rsa() returns 1, if a temporary/ephemeral RSA key is needed,
-for RSA-based strength-limited 'exportable' ciphersuites because a RSA key
-with a keysize larger than 512 bits is installed.
-
-These functions apply to SSL/TLS servers only.
-
-=head1 NOTES
-
-When using a cipher with RSA authentication, an ephemeral RSA key exchange
-can take place. In this case the session data are negotiated using the
-ephemeral/temporary RSA key and the RSA key supplied and certified
-by the certificate chain is only used for signing.
-
-Under previous export restrictions, ciphers with RSA keys shorter (512 bits)
-than the usual key length of 1024 bits were created. To use these ciphers
-with RSA keys of usual length, an ephemeral key exchange must be performed,
-as the normal (certified) key cannot be directly used.
-
-Using ephemeral RSA key exchange yields forward secrecy, as the connection
-can only be decrypted, when the RSA key is known. By generating a temporary
-RSA 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) RSA key, as this key was
-used for signing only. The downside is that creating a RSA key is
-computationally expensive.
-
-Additionally, the use of ephemeral RSA key exchange is only allowed in
-the TLS standard, when the RSA key can be used for signing only, that is
-for export ciphers. Using ephemeral RSA key exchange for other purposes
-violates the standard and can break interoperability with clients.
-It is therefore strongly recommended to not use ephemeral RSA key
-exchange and use EDH (Ephemeral Diffie-Hellman) key exchange instead
-in order to achieve forward secrecy (see
-L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
-
-On OpenSSL servers ephemeral RSA key exchange is therefore disabled by default
-and must be explicitly enabled using the SSL_OP_EPHEMERAL_RSA option of
-L<SSL_CTX_set_options(3)|SSL_CTX_set_options(3)>, violating the TLS/SSL
-standard. When ephemeral RSA key exchange is required for export ciphers,
-it will automatically be used without this option!
-
-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 RSA 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 SSL_OP_EPHEMERAL_RSA
-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.
-
-The B<tmp_rsa_callback> is called with the B<keylength> needed and
-the B<is_export> information. The B<is_export> flag is set, when the
-ephemeral RSA key exchange is performed with an export cipher.
-
-=head1 EXAMPLES
-
-Generate temporary RSA keys to prepare ephemeral RSA key exchange. As the
-generation of a RSA 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.
-
- ...
- /* Set up ephemeral RSA stuff */
- RSA *rsa_512 = NULL;
- RSA *rsa_1024 = NULL;
-
- rsa_512 = RSA_generate_key(512,RSA_F4,NULL,NULL);
- if (rsa_512 == NULL)
- evaluate_error_queue();
-
- rsa_1024 = RSA_generate_key(1024,RSA_F4,NULL,NULL);
- if (rsa_1024 == NULL)
- evaluate_error_queue();
-
- ...
-
- RSA *tmp_rsa_callback(SSL *s, int is_export, int keylength)
- {
- RSA *rsa_tmp=NULL;
-
- 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);
- }
-
-=head1 RETURN VALUES
-
-SSL_CTX_set_tmp_rsa_callback() and SSL_set_tmp_rsa_callback() do not return
-diagnostic output.
-
-SSL_CTX_set_tmp_rsa() and SSL_set_tmp_rsa() do return 1 on success and 0
-on failure. Check the error queue to find out the reason of failure.
-
-SSL_CTX_need_tmp_rsa() and SSL_need_tmp_rsa() return 1 if a temporary
-RSA key is needed and 0 otherwise.
-
-=head1 SEE ALSO
-
-L<ssl(3)|ssl(3)>, L<SSL_CTX_set_cipher_list(3)|SSL_CTX_set_cipher_list(3)>,
-L<SSL_CTX_set_options(3)|SSL_CTX_set_options(3)>,
-L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
-L<SSL_new(3)|SSL_new(3)>, L<ciphers(1)|ciphers(1)>
-
-=cut
projects / cassiopeia.git / blobdiff