/usr/man/cat.3/EVP_SealInit.3

EVP_SealInit(3)              OpenSSL              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, const 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_aes_256_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.

1.0.2t               Last change: 2019-09-10                    1

EVP_SealInit(3)              OpenSSL              EVP_SealInit(3)

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.

1.0.2t               Last change: 2019-09-10                    2

See also EVP_SealFinal(3)
See also EVP_SealUpdate(3)