EVP_SealInit(3)

     NAME
          EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope
          encryption

     SYNOPSIS
           #include <openssl/evp.h>

           int EVP_SealInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char **ek,
                          int *ekl, unsigned char *iv,EVP_PKEY **pubk, int npubk);
           int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
                   int *outl, unsigned char *in, int inl);
           int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
                   int *outl);


     DESCRIPTION
          The EVP envelope routines are a high level interface to
          envelope encryption. They generate a random key and IV (if
          required) then "envelope" it by using public key encryption.
          Data can then be encrypted using this key.

          EVP_SealInit() initializes a cipher context ctx for
          encryption with cipher type using a random secret key and
          IV. type is normally supplied by a function such as
          EVP_des_cbc(). The secret key is encrypted using one or more
          public keys, this allows the same encrypted data to be
          decrypted using any of the corresponding private keys. ek is
          an array of buffers where the public key encrypted secret
          key will be written, each buffer must contain enough room
          for the corresponding encrypted key: that is ek[i] must have
          room for EVP_PKEY_size(pubk[i]) bytes. The actual size of
          each encrypted secret key is written to the array ekl. pubk
          is an array of npubk public keys.

          The iv parameter is a buffer where the generated IV is
          written to. It must contain enough room for the
          corresponding cipher's IV, as determined by (for example)
          EVP_CIPHER_iv_length(type).

          If the cipher does not require an IV then the iv parameter
          is ignored and can be NULL.

          EVP_SealUpdate() and EVP_SealFinal() have exactly the same
          properties as the EVP_EncryptUpdate() and EVP_EncryptFinal()
          routines, as documented on the EVP_EncryptInit(3) manual
          page.

     RETURN VALUES
          EVP_SealInit() returns 0 on error or npubk if successful.

          EVP_SealUpdate() and EVP_SealFinal() return 1 for success
          and 0 for failure.
     NOTES
          Because a random secret key is generated the random number
          generator must be seeded before calling EVP_SealInit().

          The public key must be RSA because it is the only OpenSSL
          public key algorithm that supports key transport.

          Envelope encryption is the usual method of using public key
          encryption on large amounts of data, this is because public
          key encryption is slow but symmetric encryption is fast. So
          symmetric encryption is used for bulk encryption and the
          small random symmetric key used is transferred using public
          key encryption.

          It is possible to call EVP_SealInit() twice in the same way
          as EVP_EncryptInit(). The first call should have npubk set
          to 0 and (after setting any cipher parameters) it should be
          called again with type set to NULL.

     SEE ALSO
          evp(3), rand(3), EVP_EncryptInit(3), EVP_OpenInit(3)

     HISTORY
          EVP_SealFinal() did not return a value before OpenSSL 0.9.7.