1EVP_SEALINIT(3)                     OpenSSL                    EVP_SEALINIT(3)
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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 EVP_PKEY_size(pubk[i])
32       bytes. The actual size of each encrypted secret key is written to the
33       array ekl. pubk is an array of npubk public keys.
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35       The iv parameter is a buffer where the generated IV is written to. It
36       must contain enough room for the corresponding cipher's IV, as
37       determined by (for example) EVP_CIPHER_iv_length(type).
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39       If the cipher does not require an IV then the iv parameter is ignored
40       and can be NULL.
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42       EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties
43       as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as
44       documented on the EVP_EncryptInit(3) manual page.
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RETURN VALUES

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

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

73       evp(7), RAND_bytes(3), EVP_EncryptInit(3), EVP_OpenInit(3), RAND(7)
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76       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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78       Licensed under the OpenSSL license (the "License").  You may not use
79       this file except in compliance with the License.  You can obtain a copy
80       in the file LICENSE in the source distribution or at
81       <https://www.openssl.org/source/license.html>.
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851.1.1q                            2022-07-07                   EVP_SEALINIT(3)
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