5 CMS_decrypt - decrypt content from a CMS envelopedData structure
9 #include <openssl/cms.h>
11 int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
15 CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData
16 structure. B<pkey> is the private key of the recipient, B<cert> is the
17 recipient's certificate, B<out> is a BIO to write the content to and
18 B<flags> is an optional set of flags.
20 The B<dcont> parameter is used in the rare case where the encrypted content
21 is detached. It will normally be set to NULL.
25 OpenSSL_add_all_algorithms() (or equivalent) should be called before using this
26 function or errors about unknown algorithms will occur.
28 Although the recipients certificate is not needed to decrypt the data it is
29 needed to locate the appropriate (of possible several) recipients in the CMS
32 If B<cert> is set to NULL all possible recipients are tried. This case however
33 is problematic. To thwart the MMA attack (Bleichenbacher's attack on
34 PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or
35 not. If no recipient succeeds then a random symmetric key is used to decrypt
36 the content: this will typically output garbage and may (but is not guaranteed
37 to) ultimately return a padding error only. If CMS_decrypt() just returned an
38 error when all recipient encrypted keys failed to decrypt an attacker could
39 use this in a timing attack. If the special flag B<CMS_DEBUG_DECRYPT> is set
40 then the above behaviour is modified and an error B<is> returned if no
41 recipient encrypted key can be decrypted B<without> generating a random
42 content encryption key. Applications should use this flag with
43 B<extreme caution> especially in automated gateways as it can leave them
46 It is possible to determine the correct recipient key by other means (for
47 example looking them up in a database) and setting them in the CMS structure
48 in advance using the CMS utility functions such as CMS_set1_pkey(). In this
49 case both B<cert> and B<pkey> should be set to NULL.
51 To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key()
52 and CMS_ReceipientInfo_decrypt() should be called before CMS_decrypt() and
53 B<cert> and B<pkey> set to NULL.
55 The following flags can be passed in the B<flags> parameter.
57 If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
58 from the content. If the content is not of type B<text/plain> then an error is
63 CMS_decrypt() returns either 1 for success or 0 for failure.
64 The error can be obtained from ERR_get_error(3)
68 The lack of single pass processing and the need to hold all data in memory as
69 mentioned in CMS_verify() also applies to CMS_decrypt().
73 L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_encrypt(3)|CMS_encrypt(3)>
77 CMS_decrypt() was added to OpenSSL 0.9.8