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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- EVP envelope encryption .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" The \s-1EVP\s0 envelope routines are a high-level interface to envelope encryption. They generate a random key and \s-1IV\s0 (if required) then \&\*(L"envelope\*(R" it by using public key encryption. Data can then be encrypted using this key. .PP \&\fBEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption with cipher \fBtype\fR using a random secret key and \s-1IV.\s0 \fBtype\fR is normally supplied by a function such as \fBEVP_aes_256_cbc()\fR. 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. \fBek\fR 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 \&\fBek[i]\fR must have room for \fBEVP_PKEY_size(pubk[i])\fR bytes. The actual size of each encrypted secret key is written to the array \fBekl\fR. \fBpubk\fR is an array of \fBnpubk\fR public keys. .PP The \fBiv\fR parameter is a buffer where the generated \s-1IV\s0 is written to. It must contain enough room for the corresponding cipher's \s-1IV,\s0 as determined by (for example) EVP_CIPHER_iv_length(type). .PP If the cipher does not require an \s-1IV\s0 then the \fBiv\fR parameter is ignored and can be \fB\s-1NULL\s0\fR. .PP \&\fBEVP_SealUpdate()\fR and \fBEVP_SealFinal()\fR have exactly the same properties as the \fBEVP_EncryptUpdate()\fR and \fBEVP_EncryptFinal()\fR routines, as documented on the \fBEVP_EncryptInit\fR\|(3) manual page. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful. .PP \&\fBEVP_SealUpdate()\fR and \fBEVP_SealFinal()\fR return 1 for success and 0 for failure. .SH "NOTES" .IX Header "NOTES" Because a random secret key is generated the random number generator must be seeded when \fBEVP_SealInit()\fR is called. If the automatic seeding or reseeding of the OpenSSL \s-1CSPRNG\s0 fails due to external circumstances (see \s-1\fBRAND\s0\fR\|(7)), the operation will fail. .PP The public key must be \s-1RSA\s0 because it is the only OpenSSL public key algorithm that supports key transport. .PP 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. .PP It is possible to call \fBEVP_SealInit()\fR twice in the same way as \&\fBEVP_EncryptInit()\fR. The first call should have \fBnpubk\fR set to 0 and (after setting any cipher parameters) it should be called again with \fBtype\fR set to \s-1NULL.\s0 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBevp\fR\|(7), \fBRAND_bytes\fR\|(3), \&\fBEVP_EncryptInit\fR\|(3), \&\fBEVP_OpenInit\fR\|(3), \&\s-1\fBRAND\s0\fR\|(7) .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.