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=pod
=head1 NAME
EVP_OpenInit, EVP_OpenUpdate, EVP_OpenFinal - EVP envelope decryption
=head1 SYNOPSIS
#include <openssl/evp.h>
int EVP_OpenInit(EVP_CIPHER_CTX *ctx,EVP_CIPHER *type,unsigned char *ek,
int ekl,unsigned char *iv,EVP_PKEY *priv);
int EVP_OpenUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, unsigned char *in, int inl);
int EVP_OpenFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl);
=head1 DESCRIPTION
The EVP envelope routines are a high level interface to envelope
decryption. They decrypt a public key encrypted symmetric key and
then decrypt data using it.
EVP_OpenInit() initializes a cipher context B<ctx> for decryption
with cipher B<type>. It decrypts the encrypted symmetric key of length
B<ekl> bytes passed in the B<ek> parameter using the private key B<priv>.
The IV is supplied in the B<iv> parameter.
EVP_OpenUpdate() and EVP_OpenFinal() have exactly the same properties
as the EVP_DecryptUpdate() and EVP_DecryptFinal() routines, as
documented on the L<EVP_EncryptInit(3)|EVP_EncryptInit(3)> manual
page.
=head1 NOTES
It is possible to call EVP_OpenInit() twice in the same way as
EVP_DecryptInit(). The first call should have B<priv> set to NULL
and (after setting any cipher parameters) it should be called again
with B<type> set to NULL.
If the cipher passed in the B<type> parameter is a variable length
cipher then the key length will be set to the value of the recovered
key length. If the cipher is a fixed length cipher then the recovered
key length must match the fixed cipher length.
=head1 RETURN VALUES
EVP_OpenInit() returns 0 on error or a non zero integer (actually the
recovered secret key size) if successful.
EVP_OpenUpdate() returns 1 for success or 0 for failure.
EVP_OpenFinal() returns 0 if the decrypt failed or 1 for success.
=head1 SEE ALSO
L<evp(3)|evp(3)>, L<rand(3)|rand(3)>,
L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>,
L<EVP_SealInit(3)|EVP_SealInit(3)>
=cut
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