EVP_PKEY_CTX_set_cb(3)

NAME

       EVP_PKEY_keygen_init, EVP_PKEY_keygen, EVP_PKEY_paramgen_init,
       EVP_PKEY_paramgen, EVP_PKEY_CTX_set_cb, EVP_PKEY_CTX_get_cb,
       EVP_PKEY_CTX_get_keygen_info, EVP_PKEVP_PKEY_CTX_set_app_data,
       EVP_PKEY_CTX_get_app_data - key and parameter generation functions

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_PKEY_keygen_init(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_keygen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
        int EVP_PKEY_paramgen_init(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_paramgen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);

        typedef int EVP_PKEY_gen_cb(EVP_PKEY_CTX *ctx);

        void EVP_PKEY_CTX_set_cb(EVP_PKEY_CTX *ctx, EVP_PKEY_gen_cb *cb);
        EVP_PKEY_gen_cb *EVP_PKEY_CTX_get_cb(EVP_PKEY_CTX *ctx);

        int EVP_PKEY_CTX_get_keygen_info(EVP_PKEY_CTX *ctx, int idx);

        void EVP_PKEY_CTX_set_app_data(EVP_PKEY_CTX *ctx, void *data);
        void *EVP_PKEY_CTX_get_app_data(EVP_PKEY_CTX *ctx);

DESCRIPTION

       The EVP_PKEY_keygen_init() function initializes a public key algorithm
       context using key pkey for a key genration operation.

       The EVP_PKEY_keygen() function performs a key generation operation, the
       generated key is written to ppkey.

       The functions EVP_PKEY_paramgen_init() and EVP_PKEY_paramgen() are sim-
       ilar except parameters are generated.

       The function EVP_PKEY_set_cb() sets the key or parameter generation
       callback to cb. The function EVP_PKEY_CTX_get_cb() returns the key or
       parameter generation callback.

       The function EVP_PKEY_CTX_get_keygen_info() returns parameters associ-
       ated with the generation operation. If idx is -1 the total number of
       parameters available is returned. Any non negative value returns the
       value of that parameter. EVP_PKEY_CTX_gen_keygen_info() with a non-neg-
       ative value for idx should only be called within the generation call-
       back.

       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 "cancel" button.

       The functions EVP_PKEY_CTX_set_app_data() and
       EVP_PKEY_CTX_get_app_data() 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 "progress dialog".

NOTES

       After the call to EVP_PKEY_keygen_init() or EVP_PKEY_paramgen_init()
       algorithm specific control operations can be performed to set any
       appropriate parameters for the operation.

       The functions EVP_PKEY_keygen() and EVP_PKEY_paramgen() can be called
       more than once on the same context if several operations are performed
       using the same parameters.

       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 genera-
       tion. Others might not even call the callback.

       The operation performed by key or parameter generation depends on the
       algorithm used. In some cases (e.g. EC with a supplied named curve) the
       "generation" option merely sets the appropriate fields in an EVP_PKEY
       structure.

       In OpenSSL an EVP_PKEY 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 "key pair". A private
       key can be used in functions which require the use of a public key or
       parameters.

RETURN VALUES

       EVP_PKEY_keygen_init(), EVP_PKEY_paramgen_init(), EVP_PKEY_keygen() and
       EVP_PKEY_paramgen() 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.

EXAMPLES

       Generate a 2048 bit RSA key:

        #include <openssl/evp.h>
        #include <openssl/rsa.h>

        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 */

        /* Generate key */
        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
               /* Error */

       Generate a key from a set of parameters:

        #include <openssl/evp.h>
        #include <openssl/rsa.h>

        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 */

        /* Generate key */
        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
               /* Error */

       Example of generation callback for OpenSSL public key implementations:

        /* Application data is a BIO to output status to */

        EVP_PKEY_CTX_set_app_data(ctx, status_bio);

        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='\n';
               BIO_write(b,&c,1);
               (void)BIO_flush(b);
               return 1;
               }

SEE ALSO

       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3),
       EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3),
       EVP_PKEY_derive(3)

HISTORY

       These functions were first added to OpenSSL 1.0.0.

1.0.2t                            2019-09-10                EVP_PKEY_keygen(3)