| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | =pod |
| 2 | |
| 3 | =head1 NAME |
| 4 | |
| 5 | CMS_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 | |
| 16 | CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData |
| 17 | structure. B<pkey> is the private key of the recipient, B<cert> is the |
| 18 | recipient's certificate, B<out> is a BIO to write the content to and |
| 19 | B<flags> is an optional set of flags. |
| 20 | |
| 21 | The B<dcont> parameter is used in the rare case where the encrypted content |
| 22 | is detached. It will normally be set to NULL. |
| 23 | |
| 24 | =head1 NOTES |
| 25 | |
| 26 | Although the recipients certificate is not needed to decrypt the data it is |
| 27 | needed to locate the appropriate (of possible several) recipients in the CMS |
| 28 | structure. |
| 29 | |
| 30 | If B<cert> is set to NULL all possible recipients are tried. This case however |
| 31 | is problematic. To thwart the MMA attack (Bleichenbacher's attack on |
| 32 | PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or |
| 33 | not. If no recipient succeeds then a random symmetric key is used to decrypt |
| 34 | the content: this will typically output garbage and may (but is not guaranteed |
| 35 | to) ultimately return a padding error only. If CMS_decrypt() just returned an |
| 36 | error when all recipient encrypted keys failed to decrypt an attacker could |
| 37 | use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set |
| 38 | then the above behaviour is modified and an error B<is> returned if no |
| 39 | recipient encrypted key can be decrypted B<without> generating a random |
| 40 | content encryption key. Applications should use this flag with |
| 41 | B<extreme caution> especially in automated gateways as it can leave them |
| 42 | open to attack. |
| 43 | |
| 44 | It is possible to determine the correct recipient key by other means (for |
| 45 | example looking them up in a database) and setting them in the CMS structure |
| 46 | in advance using the CMS utility functions such as CMS_set1_pkey(). In this |
| 47 | case both B<cert> and B<pkey> should be set to NULL. |
| 48 | |
| 49 | To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() |
| 50 | and CMS_RecipientInfo_decrypt() should be called before CMS_decrypt() and |
| 51 | B<cert> and B<pkey> set to NULL. |
| 52 | |
| 53 | The following flags can be passed in the B<flags> parameter. |
| 54 | |
| 55 | If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted |
| 56 | from the content. If the content is not of type B<text/plain> then an error is |
| 57 | returned. |
| 58 | |
| 59 | =head1 RETURN VALUES |
| 60 | |
| 61 | CMS_decrypt() returns either 1 for success or 0 for failure. |
| 62 | The error can be obtained from ERR_get_error(3) |
| 63 | |
| 64 | =head1 BUGS |
| 65 | |
| 66 | The lack of single pass processing and the need to hold all data in memory as |
| 67 | mentioned in CMS_verify() also applies to CMS_decrypt(). |
| 68 | |
| 69 | =head1 SEE ALSO |
| 70 | |
| 71 | L<ERR_get_error(3)>, L<CMS_encrypt(3)> |
| 72 | |
| 73 | =head1 COPYRIGHT |
| 74 | |
| 75 | Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved. |
| 76 | |
| 77 | Licensed under the OpenSSL license (the "License"). You may not use |
| 78 | this file except in compliance with the License. You can obtain a copy |
| 79 | in the file LICENSE in the source distribution or at |
| 80 | L<https://www.openssl.org/source/license.html>. |
| 81 | |
| 82 | =cut |