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