=pod
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=head1 NAME
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EVP_OpenInit, EVP_OpenUpdate, EVP_OpenFinal - EVP envelope decryption
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_OpenInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char *ek,
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int ekl, unsigned char *iv, EVP_PKEY *priv);
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int EVP_OpenUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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int EVP_OpenFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
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=head1 DESCRIPTION
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The EVP envelope routines are a high-level interface to envelope
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decryption. They decrypt a public key encrypted symmetric key and
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then decrypt data using it.
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EVP_OpenInit() initializes a cipher context B<ctx> for decryption
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with cipher B<type>. It decrypts the encrypted symmetric key of length
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B<ekl> bytes passed in the B<ek> parameter using the private key B<priv>.
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The IV is supplied in the B<iv> parameter.
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EVP_OpenUpdate() and EVP_OpenFinal() have exactly the same properties
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as the EVP_DecryptUpdate() and EVP_DecryptFinal() routines, as
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documented on the L<EVP_EncryptInit(3)> manual
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page.
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=head1 NOTES
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It is possible to call EVP_OpenInit() twice in the same way as
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EVP_DecryptInit(). The first call should have B<priv> set to NULL
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and (after setting any cipher parameters) it should be called again
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with B<type> set to NULL.
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If the cipher passed in the B<type> parameter is a variable length
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cipher then the key length will be set to the value of the recovered
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key length. If the cipher is a fixed length cipher then the recovered
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key length must match the fixed cipher length.
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=head1 RETURN VALUES
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EVP_OpenInit() returns 0 on error or a non zero integer (actually the
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recovered secret key size) if successful.
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EVP_OpenUpdate() returns 1 for success or 0 for failure.
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EVP_OpenFinal() returns 0 if the decrypt failed or 1 for success.
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=head1 SEE ALSO
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L<evp(7)>, L<RAND_bytes(3)>,
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L<EVP_EncryptInit(3)>,
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L<EVP_SealInit(3)>
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=head1 COPYRIGHT
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Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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