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EVP_PKEY_CTX_get_cb.3
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The function \fIEVP_PKEY_CTX_get_cb()\fR returns the key or parameter generation callback. .PP The function \fIEVP_PKEY_CTX_get_keygen_info()\fR returns parameters associated with the generation operation. If \fBidx\fR is \-1 the total number of parameters available is returned. Any non negative value returns the value of that parameter. \fIEVP_PKEY_CTX_gen_keygen_info()\fR with a non-negative value for \&\fBidx\fR should only be called within the generation callback. .PP If the callback returns 0 then the key genration operation is aborted and an error occurs. This might occur during a time consuming operation where a user clicks on a \*(L"cancel\*(R" button. .PP The functions \fIEVP_PKEY_CTX_set_app_data()\fR and \fIEVP_PKEY_CTX_get_app_data()\fR set and retrieve an opaque pointer. This can be used to set some application defined value which can be retrieved in the callback: for example a handle which is used to update a \*(L"progress dialog\*(R". .SH "NOTES" .IX Header "NOTES" After the call to \fIEVP_PKEY_keygen_init()\fR or \fIEVP_PKEY_paramgen_init()\fR algorithm specific control operations can be performed to set any appropriate parameters for the operation. .PP The functions \fIEVP_PKEY_keygen()\fR and \fIEVP_PKEY_paramgen()\fR can be called more than once on the same context if several operations are performed using the same parameters. .PP The meaning of the parameters passed to the callback will depend on the algorithm and the specifiic implementation of the algorithm. Some might not give any useful information at all during key or parameter generation. Others might not even call the callback. .PP The operation performed by key or parameter generation depends on the algorithm used. In some cases (e.g. \s-1EC\s0 with a supplied named curve) the \*(L"generation\*(R" option merely sets the appropriate fields in an \s-1EVP_PKEY\s0 structure. .PP In OpenSSL an \s-1EVP_PKEY\s0 structure containing a private key also contains the public key components and parameters (if any). An OpenSSL private key is equivalent to what some libraries call a \*(L"key pair\*(R". A private key can be used in functions which require the use of a public key or parameters. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fIEVP_PKEY_keygen_init()\fR, \fIEVP_PKEY_paramgen_init()\fR, \fIEVP_PKEY_keygen()\fR and \&\fIEVP_PKEY_paramgen()\fR return 1 for success and 0 or a negative value for failure. In particular a return value of \-2 indicates the operation is not supported by the public key algorithm. .SH "EXAMPLES" .IX Header "EXAMPLES" Generate a 2048 bit \s-1RSA\s0 key: .PP .Vb 2 \& #include <openssl/evp.h> \& #include <openssl/rsa.h> .Ve .PP .Vb 9 \& EVP_PKEY_CTX *ctx; \& EVP_PKEY *pkey = NULL; \& ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, NULL); \& if (!ctx) \& /* Error occurred */ \& if (EVP_PKEY_keygen_init(ctx) <= 0) \& /* Error */ \& if (EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048) <= 0) \& /* Error */ .Ve .PP .Vb 3 \& /* Generate key */ \& if (EVP_PKEY_keygen(ctx, &pkey) <= 0) \& /* Error */ .Ve .PP Generate a key from a set of parameters: .PP .Vb 2 \& #include <openssl/evp.h> \& #include <openssl/rsa.h> .Ve .PP .Vb 8 \& EVP_PKEY_CTX *ctx; \& EVP_PKEY *pkey = NULL, *param; \& /* Assumed param is set up already */ \& ctx = EVP_PKEY_CTX_new(param); \& if (!ctx) \& /* Error occurred */ \& if (EVP_PKEY_keygen_init(ctx) <= 0) \& /* Error */ .Ve .PP .Vb 3 \& /* Generate key */ \& if (EVP_PKEY_keygen(ctx, &pkey) <= 0) \& /* Error */ .Ve .PP Example of generation callback for OpenSSL public key implementations: .PP .Vb 1 \& /* Application data is a BIO to output status to */ .Ve .PP .Vb 1 \& EVP_PKEY_CTX_set_app_data(ctx, status_bio); .Ve .PP .Vb 14 \& static int genpkey_cb(EVP_PKEY_CTX *ctx) \& { \& char c='*'; \& BIO *b = EVP_PKEY_CTX_get_app_data(ctx); \& int p; \& p = EVP_PKEY_CTX_get_keygen_info(ctx, 0); \& if (p == 0) c='.'; \& if (p == 1) c='+'; \& if (p == 2) c='*'; \& if (p == 3) c='\en'; \& BIO_write(b,&c,1); \& (void)BIO_flush(b); \& return 1; \& } .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIEVP_PKEY_CTX_new\fR\|(3), \&\fIEVP_PKEY_encrypt\fR\|(3), \&\fIEVP_PKEY_decrypt\fR\|(3), \&\fIEVP_PKEY_sign\fR\|(3), \&\fIEVP_PKEY_verify\fR\|(3), \&\fIEVP_PKEY_verify_recover\fR\|(3), \&\fIEVP_PKEY_derive\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" These functions were first added to OpenSSL 1.0.0.