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_get_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_get_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 when
       EVP_SealInit() is called.  If the automatic seeding or reseeding of the OpenSSL CSPRNG
       fails due to external circumstances (see RAND(7)), the operation will fail.

       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(7), RAND_bytes(3), EVP_EncryptInit(3), EVP_OpenInit(3), RAND(7)

COPYRIGHT

       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.