1=pod 2 3=head1 NAME 4 5CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, CMS_decrypt_set1_pkey - decrypt 6content from a CMS envelopedData structure 7 8=head1 SYNOPSIS 9 10 #include <openssl/cms.h> 11 12 int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, 13 BIO *dcont, BIO *out, unsigned int flags); 14 int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms, 15 EVP_PKEY *pk, X509 *cert, X509 *peer); 16 int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert); 17 18=head1 DESCRIPTION 19 20CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData 21or AuthEnvelopedData structure. B<pkey> is the private key of the recipient, 22B<cert> is the recipient's certificate, B<out> is a BIO to write the content to 23and B<flags> is an optional set of flags. 24 25The B<dcont> parameter is used in the rare case where the encrypted content 26is detached. It will normally be set to NULL. 27 28CMS_decrypt_set1_pkey_and_peer() associates the private key B<pkey>, the 29corresponding certificate B<cert> and the originator certificate B<peer> with 30the CMS_ContentInfo structure B<cms>. 31 32CMS_decrypt_set1_pkey() associates the private key B<pkey>, corresponding 33certificate B<cert> with the CMS_ContentInfo structure B<cms>. 34 35=head1 NOTES 36 37Although the recipients certificate is not needed to decrypt the data it is 38needed to locate the appropriate (of possible several) recipients in the CMS 39structure. 40 41If B<cert> is set to NULL all possible recipients are tried. This case however 42is problematic. To thwart the MMA attack (Bleichenbacher's attack on 43PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or 44not. If no recipient succeeds then a random symmetric key is used to decrypt 45the content: this will typically output garbage and may (but is not guaranteed 46to) ultimately return a padding error only. If CMS_decrypt() just returned an 47error when all recipient encrypted keys failed to decrypt an attacker could 48use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set 49then the above behaviour is modified and an error B<is> returned if no 50recipient encrypted key can be decrypted B<without> generating a random 51content encryption key. Applications should use this flag with 52B<extreme caution> especially in automated gateways as it can leave them 53open to attack. 54 55It is possible to determine the correct recipient key by other means (for 56example looking them up in a database) and setting them in the CMS structure 57in advance using the CMS utility functions such as CMS_set1_pkey(). In this 58case both B<cert> and B<pkey> should be set to NULL. 59 60To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() 61and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and 62B<cert> and B<pkey> set to NULL. 63 64The following flags can be passed in the B<flags> parameter. 65 66If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted 67from the content. If the content is not of type B<text/plain> then an error is 68returned. 69 70=head1 RETURN VALUES 71 72CMS_decrypt() returns either 1 for success or 0 for failure. 73The error can be obtained from ERR_get_error(3) 74 75=head1 BUGS 76 77The lack of single pass processing and the need to hold all data in memory as 78mentioned in CMS_verify() also applies to CMS_decrypt(). 79 80=head1 SEE ALSO 81 82L<ERR_get_error(3)>, L<CMS_encrypt(3)> 83 84=head1 HISTORY 85 86B<CMS_decrypt_set1_pkey_and_peer> was added in OpenSSL 3.0. 87 88=head1 COPYRIGHT 89 90Copyright 2008-2020 The OpenSSL Project Authors. All Rights Reserved. 91 92Licensed under the Apache License 2.0 (the "License"). You may not use 93this file except in compliance with the License. You can obtain a copy 94in the file LICENSE in the source distribution or at 95L<https://www.openssl.org/source/license.html>. 96 97=cut 98