NetBSD/lib/libcrypto/man/EVP_SealInit.3

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.\" $NetBSD: EVP_SealInit.3,v 1.5 2001/04/12 10:45:37 itojun Exp $
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.\" ======================================================================
.\"
.IX Title "EVP_SealInit 3"
.TH EVP_SealInit 3 "0.9.6a" "2001-04-12" "OpenSSL"
.UC
.SH "NAME"
EVP_SealInit, EVP_SealUpdate, EVP_SealFinal \- \s-1EVP\s0 envelope encryption
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
.Ve
.Vb 6
\& int EVP_SealInit(EVP_CIPHER_CTX *ctx, 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 then \*(L"envelope\*(R" it by
using public key encryption. Data can then be encrypted using this
key.
.PP
\&\fIEVP_SealInit()\fR initializes a cipher context \fBctx\fR for encryption
with cipher \fBtype\fR using a random secret key and \s-1IV\s0 supplied in
the \fBiv\fR parameter. \fBtype\fR is normally supplied by a function such
as \fIEVP_des_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
\&\fIEVP_SealUpdate()\fR and \fIEVP_SealFinal()\fR have exactly the same properties
as the \fIEVP_EncryptUpdate()\fR and \fIEVP_EncryptFinal()\fR routines, as
documented on the EVP_EncryptInit(3) manual
page.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_SealInit()\fR returns 0 on error or \fBnpubk\fR if successful.
.PP
\&\fIEVP_SealUpdate()\fR and \fIEVP_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 before calling \fIEVP_SealInit()\fR.
.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 \fIEVP_SealInit()\fR twice in the same way as
\&\fIEVP_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"
openssl_evp(3), openssl_rand(3),
EVP_EncryptInit(3),
EVP_OpenInit(3)
.SH "HISTORY"
.IX Header "HISTORY"