NAME    [Toc]    [Back]

       EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope
       encryption

SYNOPSIS    [Toc]    [Back]

        #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    [Toc]    [Back]

       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_EncryptFi-
       nal() routines, as documented on the EVP_EncryptInit(3)
       manual page.

RETURN VALUES    [Toc]    [Back]

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

       EVP_SealUpdate() and EVP_SealFinal() return 1 for success
       and 0 for failure.

NOTES    [Toc]    [Back]

       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    [Toc]    [Back]

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

HISTORY    [Toc]    [Back]

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


OpenBSD 3.6                 2003-05-11                          2