1EVP_SEALINIT(3ossl)                 OpenSSL                EVP_SEALINIT(3ossl)
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NAME

6       EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption
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SYNOPSIS

9        #include <openssl/evp.h>
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11        int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
12                         unsigned char **ek, int *ekl, unsigned char *iv,
13                         EVP_PKEY **pubk, int npubk);
14        int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
15                           int *outl, unsigned char *in, int inl);
16        int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
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DESCRIPTION

19       The EVP envelope routines are a high-level interface to envelope
20       encryption. They generate a random key and IV (if required) then
21       "envelope" it by using public key encryption. Data can then be
22       encrypted using this key.
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24       EVP_SealInit() initializes a cipher context ctx for encryption with
25       cipher type using a random secret key and IV. type is normally supplied
26       by a function such as EVP_aes_256_cbc(). The secret key is encrypted
27       using one or more public keys, this allows the same encrypted data to
28       be decrypted using any of the corresponding private keys. ek is an
29       array of buffers where the public key encrypted secret key will be
30       written, each buffer must contain enough room for the corresponding
31       encrypted key: that is ek[i] must have room for
32       EVP_PKEY_get_size(pubk[i]) bytes. The actual size of each encrypted
33       secret key is written to the array ekl. pubk is an array of npubk
34       public keys.
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36       The iv parameter is a buffer where the generated IV is written to. It
37       must contain enough room for the corresponding cipher's IV, as
38       determined by (for example) EVP_CIPHER_get_iv_length(type).
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40       If the cipher does not require an IV then the iv parameter is ignored
41       and can be NULL.
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43       EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties
44       as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as
45       documented on the EVP_EncryptInit(3) manual page.
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RETURN VALUES

48       EVP_SealInit() returns 0 on error or npubk if successful.
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50       EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for
51       failure.
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NOTES

54       Because a random secret key is generated the random number generator
55       must be seeded when EVP_SealInit() is called.  If the automatic seeding
56       or reseeding of the OpenSSL CSPRNG fails due to external circumstances
57       (see RAND(7)), the operation will fail.
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59       The public key must be RSA because it is the only OpenSSL public key
60       algorithm that supports key transport.
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62       Envelope encryption is the usual method of using public key encryption
63       on large amounts of data, this is because public key encryption is slow
64       but symmetric encryption is fast. So symmetric encryption is used for
65       bulk encryption and the small random symmetric key used is transferred
66       using public key encryption.
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68       It is possible to call EVP_SealInit() twice in the same way as
69       EVP_EncryptInit(). The first call should have npubk set to 0 and (after
70       setting any cipher parameters) it should be called again with type set
71       to NULL.
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SEE ALSO

74       evp(7), RAND_bytes(3), EVP_EncryptInit(3), EVP_OpenInit(3), RAND(7)
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77       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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79       Licensed under the Apache License 2.0 (the "License").  You may not use
80       this file except in compliance with the License.  You can obtain a copy
81       in the file LICENSE in the source distribution or at
82       <https://www.openssl.org/source/license.html>.
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863.1.1                             2023-08-31               EVP_SEALINIT(3ossl)
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