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>.

3.0.13                                             2025-09-18                                 EVP_SEALINIT(3SSL)