1=pod 2 3=head1 NAME 4 5CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, 6CMS_decrypt_set1_pkey, CMS_decrypt_set1_password 7- decrypt content from a CMS envelopedData structure 8 9=head1 SYNOPSIS 10 11 #include <openssl/cms.h> 12 13 int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, 14 BIO *dcont, BIO *out, unsigned int flags); 15 int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms, 16 EVP_PKEY *pk, X509 *cert, X509 *peer); 17 int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert); 18 int CMS_decrypt_set1_password(CMS_ContentInfo *cms, 19 unsigned char *pass, ossl_ssize_t passlen); 20 21=head1 DESCRIPTION 22 23CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData 24or AuthEnvelopedData structure. I<pkey> is the private key of the recipient, 25I<cert> is the recipient's certificate, I<out> is a BIO to write the content to 26and I<flags> is an optional set of flags. 27 28The I<dcont> parameter is used in the rare case where the encrypted content 29is detached. It will normally be set to NULL. 30 31CMS_decrypt_set1_pkey_and_peer() associates the private key I<pkey>, the 32corresponding certificate I<cert> and the originator certificate I<peer> with 33the CMS_ContentInfo structure I<cms>. 34 35CMS_decrypt_set1_pkey() associates the private key I<pkey> and the corresponding 36certificate I<cert> with the CMS_ContentInfo structure I<cms>. 37 38CMS_decrypt_set1_password() associates the secret I<pass> of length I<passlen> 39with the CMS_ContentInfo structure I<cms>. 40 41=head1 NOTES 42 43Although the recipients certificate is not needed to decrypt the data it is 44needed to locate the appropriate (of possible several) recipients in the CMS 45structure. 46 47If I<cert> is set to NULL all possible recipients are tried. This case however 48is problematic. To thwart the MMA attack (Bleichenbacher's attack on 49PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or 50not. If no recipient succeeds then a random symmetric key is used to decrypt 51the content: this will typically output garbage and may (but is not guaranteed 52to) ultimately return a padding error only. If CMS_decrypt() just returned an 53error when all recipient encrypted keys failed to decrypt an attacker could 54use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set 55then the above behaviour is modified and an error B<is> returned if no 56recipient encrypted key can be decrypted B<without> generating a random 57content encryption key. Applications should use this flag with 58B<extreme caution> especially in automated gateways as it can leave them 59open to attack. 60 61It is possible to determine the correct recipient key by other means (for 62example looking them up in a database) and setting them in the CMS structure 63in advance using the CMS utility functions such as CMS_set1_pkey(). In this 64case both I<cert> and I<pkey> should be set to NULL. 65 66To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() 67and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and 68I<cert> and I<pkey> set to NULL. 69 70The following flags can be passed in the I<flags> parameter. 71 72If the B<CMS_TEXT> flag is set MIME headers for type C<text/plain> are deleted 73from the content. If the content is not of type C<text/plain> then an error is 74returned. 75 76=head1 RETURN VALUES 77 78CMS_decrypt(), CMS_decrypt_set1_pkey_and_peer(), 79CMS_decrypt_set1_pkey(), and CMS_decrypt_set1_password() 80return either 1 for success or 0 for failure. 81The error can be obtained from ERR_get_error(3). 82 83=head1 BUGS 84 85The lack of single pass processing and the need to hold all data in memory as 86mentioned in CMS_verify() also applies to CMS_decrypt(). 87 88=head1 SEE ALSO 89 90L<ERR_get_error(3)>, L<CMS_encrypt(3)> 91 92=head1 HISTORY 93 94CMS_decrypt_set1_pkey_and_peer() and CMS_decrypt_set1_password() 95were added in OpenSSL 3.0. 96 97=head1 COPYRIGHT 98 99Copyright 2008-2020 The OpenSSL Project Authors. All Rights Reserved. 100 101Licensed under the Apache License 2.0 (the "License"). You may not use 102this file except in compliance with the License. You can obtain a copy 103in the file LICENSE in the source distribution or at 104L<https://www.openssl.org/source/license.html>. 105 106=cut 107
