1=pod 2 3=head1 NAME 4 5CMS_decrypt - decrypt content from a CMS envelopedData structure 6 7=head1 SYNOPSIS 8 9 #include <openssl/cms.h> 10 11 int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, 12 BIO *dcont, BIO *out, unsigned int flags); 13 14=head1 DESCRIPTION 15 16CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData 17structure. B<pkey> is the private key of the recipient, B<cert> is the 18recipient's certificate, B<out> is a BIO to write the content to and 19B<flags> is an optional set of flags. 20 21The B<dcont> parameter is used in the rare case where the encrypted content 22is detached. It will normally be set to NULL. 23 24=head1 NOTES 25 26Although the recipients certificate is not needed to decrypt the data it is 27needed to locate the appropriate (of possible several) recipients in the CMS 28structure. 29 30If B<cert> is set to NULL all possible recipients are tried. This case however 31is problematic. To thwart the MMA attack (Bleichenbacher's attack on 32PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or 33not. If no recipient succeeds then a random symmetric key is used to decrypt 34the content: this will typically output garbage and may (but is not guaranteed 35to) ultimately return a padding error only. If CMS_decrypt() just returned an 36error when all recipient encrypted keys failed to decrypt an attacker could 37use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set 38then the above behaviour is modified and an error B<is> returned if no 39recipient encrypted key can be decrypted B<without> generating a random 40content encryption key. Applications should use this flag with 41B<extreme caution> especially in automated gateways as it can leave them 42open to attack. 43 44It is possible to determine the correct recipient key by other means (for 45example looking them up in a database) and setting them in the CMS structure 46in advance using the CMS utility functions such as CMS_set1_pkey(). In this 47case both B<cert> and B<pkey> should be set to NULL. 48 49To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() 50and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and 51B<cert> and B<pkey> set to NULL. 52 53The following flags can be passed in the B<flags> parameter. 54 55If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted 56from the content. If the content is not of type B<text/plain> then an error is 57returned. 58 59=head1 RETURN VALUES 60 61CMS_decrypt() returns either 1 for success or 0 for failure. 62The error can be obtained from ERR_get_error(3) 63 64=head1 BUGS 65 66The lack of single pass processing and the need to hold all data in memory as 67mentioned in CMS_verify() also applies to CMS_decrypt(). 68 69=head1 SEE ALSO 70 71L<ERR_get_error(3)>, L<CMS_encrypt(3)> 72 73=head1 COPYRIGHT 74 75Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved. 76 77Licensed under the OpenSSL license (the "License"). You may not use 78this file except in compliance with the License. You can obtain a copy 79in the file LICENSE in the source distribution or at 80L<https://www.openssl.org/source/license.html>. 81 82=cut 83