1.\" $OpenBSD: EVP_SealInit.3,v 1.9 2023/11/16 20:27:43 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Dr. Stephen Henson <steve@openssl.org>. 5.\" Copyright (c) 2000, 2002, 2003, 2005, 2015 The OpenSSL Project. 6.\" All rights reserved. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in 17.\" the documentation and/or other materials provided with the 18.\" distribution. 19.\" 20.\" 3. All advertising materials mentioning features or use of this 21.\" software must display the following acknowledgment: 22.\" "This product includes software developed by the OpenSSL Project 23.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 24.\" 25.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 26.\" endorse or promote products derived from this software without 27.\" prior written permission. For written permission, please contact 28.\" openssl-core@openssl.org. 29.\" 30.\" 5. Products derived from this software may not be called "OpenSSL" 31.\" nor may "OpenSSL" appear in their names without prior written 32.\" permission of the OpenSSL Project. 33.\" 34.\" 6. Redistributions of any form whatsoever must retain the following 35.\" acknowledgment: 36.\" "This product includes software developed by the OpenSSL Project 37.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 38.\" 39.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 40.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 41.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 42.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 43.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 44.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 45.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 46.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 47.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 48.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 49.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 50.\" OF THE POSSIBILITY OF SUCH DAMAGE. 51.\" 52.Dd $Mdocdate: November 16 2023 $ 53.Dt EVP_SEALINIT 3 54.Os 55.Sh NAME 56.Nm EVP_SealInit , 57.Nm EVP_SealUpdate , 58.Nm EVP_SealFinal 59.Nd EVP envelope encryption 60.Sh SYNOPSIS 61.In openssl/evp.h 62.Ft int 63.Fo EVP_SealInit 64.Fa "EVP_CIPHER_CTX *ctx" 65.Fa "const EVP_CIPHER *type" 66.Fa "unsigned char **ek" 67.Fa "int *ekl" 68.Fa "unsigned char *iv" 69.Fa "EVP_PKEY **pubk" 70.Fa "int npubk" 71.Fc 72.Ft int 73.Fo EVP_SealUpdate 74.Fa "EVP_CIPHER_CTX *ctx" 75.Fa "unsigned char *out" 76.Fa "int *outl" 77.Fa "unsigned char *in" 78.Fa "int inl" 79.Fc 80.Ft int 81.Fo EVP_SealFinal 82.Fa "EVP_CIPHER_CTX *ctx" 83.Fa "unsigned char *out" 84.Fa "int *outl" 85.Fc 86.Sh DESCRIPTION 87The EVP envelope routines are a high level interface to envelope 88encryption. 89They generate a random key and IV (if required) then "envelope" it by 90using public key encryption. 91Data can then be encrypted using this key. 92.Pp 93.Fn EVP_SealInit 94initializes a cipher context 95.Fa ctx 96for encryption with cipher 97.Fa type 98using a random secret key and IV. 99.Fa type 100is normally supplied by a function such as 101.Xr EVP_aes_256_cbc 3 ; 102see 103.Xr EVP_EncryptInit 3 104for details. 105The secret key is encrypted using one or more public keys. 106This allows the same encrypted data to be decrypted using any of 107the corresponding private keys. 108.Fa ek 109is an array of buffers where the public key encrypted secret key will be 110written. 111Each buffer must contain enough room for the corresponding encrypted 112key: that is 113.Fa ek[i] 114must have room for 115.Fn EVP_PKEY_size pubk[i] 116bytes. 117The actual size of each encrypted secret key is written to the array 118.Fa ekl . 119.Fa pubk 120is an array of 121.Fa npubk 122public keys. 123.Pp 124The 125.Fa iv 126parameter is a buffer where the generated IV is written to. 127It must contain enough room for the corresponding cipher's IV, as 128determined by (for example) 129.Fn EVP_CIPHER_iv_length type . 130.Pp 131If the cipher does not require an IV then the 132.Fa iv 133parameter is ignored and can be 134.Dv NULL . 135.Pp 136.Fn EVP_SealUpdate 137and 138.Fn EVP_SealFinal 139have exactly the same properties as the 140.Xr EVP_EncryptUpdate 3 141and 142.Xr EVP_EncryptFinal 3 143routines. 144.Pp 145The public key must be RSA because it is the only OpenSSL public key 146algorithm that supports key transport. 147.Pp 148Envelope encryption is the usual method of using public key encryption 149on large amounts of data. 150This is because public key encryption is slow but symmetric encryption 151is fast. 152So symmetric encryption is used for bulk encryption and the small random 153symmetric key used is transferred using public key encryption. 154.Pp 155It is possible to call 156.Fn EVP_SealInit 157twice in the same way as 158.Xr EVP_EncryptInit 3 . 159The first call should have 160.Fa npubk 161set to 0 and (after setting any cipher parameters) it should be called 162again with 163.Fa type 164set to NULL. 165.Pp 166.Fn EVP_SealUpdate 167is implemented as a macro. 168.Sh RETURN VALUES 169.Fn EVP_SealInit 170returns 0 on error or 171.Fa npubk 172if successful. 173.Pp 174.Fn EVP_SealUpdate 175and 176.Fn EVP_SealFinal 177return 1 for success and 0 for failure. 178.Sh SEE ALSO 179.Xr evp 3 , 180.Xr EVP_EncryptInit 3 , 181.Xr EVP_OpenInit 3 182.Sh HISTORY 183.Fn EVP_SealInit , 184.Fn EVP_SealUpdate , 185and 186.Fn EVP_SealFinal 187first appeared in SSLeay 0.5.1 and have been available since 188.Ox 2.4 . 189.Pp 190.Fn EVP_SealFinal 191did not return a value before OpenSSL 0.9.7. 192