EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption
#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_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.
EVP_SealInit() returns 0 on error or
npubk if successful.
EVP_SealUpdate() and
EVP_SealFinal() return 1 for success and 0
for failure.
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 2000-2021 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>.