=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)>

=head1 HISTORY

=cut