Updated: 2021/Apr/14

EVP_SealInit(3)                     OpenSSL                    EVP_SealInit(3)

       EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption

       libcrypto, -lcrypto

        #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);

       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.

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

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

       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.

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

       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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

1.1.1i                            2020-12-10                   EVP_SealInit(3)