1CMS_DECRYPT(3)                      OpenSSL                     CMS_DECRYPT(3)
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NAME

6       CMS_decrypt - decrypt content from a CMS envelopedData structure
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SYNOPSIS

9        #include <openssl/cms.h>
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11        int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert,
12                        BIO *dcont, BIO *out, unsigned int flags);
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DESCRIPTION

15       CMS_decrypt() extracts and decrypts the content from a CMS
16       EnvelopedData structure. pkey is the private key of the recipient, cert
17       is the recipient's certificate, out is a BIO to write the content to
18       and flags is an optional set of flags.
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20       The dcont parameter is used in the rare case where the encrypted
21       content is detached. It will normally be set to NULL.
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NOTES

24       Although the recipients certificate is not needed to decrypt the data
25       it is needed to locate the appropriate (of possible several) recipients
26       in the CMS structure.
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28       If cert is set to NULL all possible recipients are tried. This case
29       however is problematic. To thwart the MMA attack (Bleichenbacher's
30       attack on PKCS #1 v1.5 RSA padding) all recipients are tried whether
31       they succeed or not. If no recipient succeeds then a random symmetric
32       key is used to decrypt the content: this will typically output garbage
33       and may (but is not guaranteed to) ultimately return a padding error
34       only. If CMS_decrypt() just returned an error when all recipient
35       encrypted keys failed to decrypt an attacker could use this in a timing
36       attack. If the special flag CMS_DEBUG_DECRYPT is set then the above
37       behaviour is modified and an error is returned if no recipient
38       encrypted key can be decrypted without generating a random content
39       encryption key. Applications should use this flag with extreme caution
40       especially in automated gateways as it can leave them open to attack.
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42       It is possible to determine the correct recipient key by other means
43       (for example looking them up in a database) and setting them in the CMS
44       structure in advance using the CMS utility functions such as
45       CMS_set1_pkey(). In this case both cert and pkey should be set to NULL.
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47       To process KEKRecipientInfo types CMS_set1_key() or
48       CMS_RecipientInfo_set0_key() and CMS_RecipientInfo_decrypt() should be
49       called before CMS_decrypt() and cert and pkey set to NULL.
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51       The following flags can be passed in the flags parameter.
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53       If the CMS_TEXT flag is set MIME headers for type text/plain are
54       deleted from the content. If the content is not of type text/plain then
55       an error is returned.
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RETURN VALUES

58       CMS_decrypt() returns either 1 for success or 0 for failure.  The error
59       can be obtained from ERR_get_error(3)
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BUGS

62       The lack of single pass processing and the need to hold all data in
63       memory as mentioned in CMS_verify() also applies to CMS_decrypt().
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SEE ALSO

66       ERR_get_error(3), CMS_encrypt(3)
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69       Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.
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71       Licensed under the OpenSSL license (the "License").  You may not use
72       this file except in compliance with the License.  You can obtain a copy
73       in the file LICENSE in the source distribution or at
74       <https://www.openssl.org/source/license.html>.
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781.1.1q                            2023-07-20                    CMS_DECRYPT(3)
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