EVP_PKEY_keygen(3)           OpenSSL           EVP_PKEY_keygen(3)


     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_PKEVP_PKEY_CTX_set_app_data, EVP_PKEY_CTX_get_app_data -
     key and parameter generation functions


      #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);


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

     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 similar except parameters are

     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 associated 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-negative value for
     idx should only be called within the generation callback.

     If the callback returns 0 then the key genration operation
     is aborted and an error occurs. This might occur during a

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EVP_PKEY_keygen(3)           OpenSSL           EVP_PKEY_keygen(3)

     time consuming operation where a user clicks on a "cancel"

     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".


     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 generation. 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


     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.


     Generate a 2048 bit RSA key:

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

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EVP_PKEY_keygen(3)           OpenSSL           EVP_PKEY_keygen(3)

      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

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

      EVP_PKEY_CTX_set_app_data(ctx, status_bio);

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EVP_PKEY_keygen(3)           OpenSSL           EVP_PKEY_keygen(3)

      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';
             return 1;


     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)


     These functions were first added to OpenSSL 1.0.0.

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