1=pod 2 3=head1 NAME 4 5EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 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); 17 18=head1 DESCRIPTION 19 20The EVP envelope routines are a high-level interface to envelope 21encryption. They generate a random key and IV (if required) then 22"envelope" it by using public key encryption. Data can then be 23encrypted using this key. 24 25EVP_SealInit() initializes a cipher context B<ctx> for encryption 26with cipher B<type> using a random secret key and IV. B<type> is normally 27supplied by a function such as EVP_aes_256_cbc(). The secret key is encrypted 28using one or more public keys, this allows the same encrypted data to be 29decrypted using any of the corresponding private keys. B<ek> is an array of 30buffers where the public key encrypted secret key will be written, each buffer 31must contain enough room for the corresponding encrypted key: that is 32B<ek[i]> must have room for B<EVP_PKEY_size(pubk[i])> bytes. The actual 33size of each encrypted secret key is written to the array B<ekl>. B<pubk> is 34an array of B<npubk> public keys. 35 36The B<iv> parameter is a buffer where the generated IV is written to. It must 37contain enough room for the corresponding cipher's IV, as determined by (for 38example) EVP_CIPHER_iv_length(type). 39 40If the cipher does not require an IV then the B<iv> parameter is ignored 41and can be B<NULL>. 42 43EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties 44as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as 45documented on the L<EVP_EncryptInit(3)> manual 46page. 47 48=head1 RETURN VALUES 49 50EVP_SealInit() returns 0 on error or B<npubk> if successful. 51 52EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for 53failure. 54 55=head1 NOTES 56 57Because a random secret key is generated the random number generator 58must be seeded when EVP_SealInit() is called. 59If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to 60external circumstances (see L<RAND(7)>), the operation will fail. 61 62The public key must be RSA because it is the only OpenSSL public key 63algorithm that supports key transport. 64 65Envelope encryption is the usual method of using public key encryption 66on large amounts of data, this is because public key encryption is slow 67but symmetric encryption is fast. So symmetric encryption is used for 68bulk encryption and the small random symmetric key used is transferred 69using public key encryption. 70 71It is possible to call EVP_SealInit() twice in the same way as 72EVP_EncryptInit(). The first call should have B<npubk> set to 0 73and (after setting any cipher parameters) it should be called again 74with B<type> set to NULL. 75 76=head1 SEE ALSO 77 78L<evp(7)>, L<RAND_bytes(3)>, 79L<EVP_EncryptInit(3)>, 80L<EVP_OpenInit(3)>, 81L<RAND(7)> 82 83=head1 COPYRIGHT 84 85Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved. 86 87Licensed under the OpenSSL license (the "License"). You may not use 88this file except in compliance with the License. You can obtain a copy 89in the file LICENSE in the source distribution or at 90L<https://www.openssl.org/source/license.html>. 91 92=cut 93