1CMS_decrypt(3) OpenSSL CMS_decrypt(3)
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6 CMS_decrypt - decrypt content from a CMS envelopedData structure
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9 #include <openssl/cms.h>
10 int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
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14 CMS_decrypt() extracts and decrypts the content from a CMS
15 EnvelopedData structure. pkey is the private key of the recipient, cert
16 is the recipient's certificate, out is a BIO to write the content to
17 and flags is an optional set of flags.
18 The dcont parameter is used in the rare case where the encrypted
20 content is detached. It will normally be set to NULL.
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23 OpenSSL_add_all_algorithms() (or equivalent) should be called before
24 using this function or errors about unknown algorithms will occur.
25 Although the recipients certificate is not needed to decrypt the data
27 it is needed to locate the appropriate (of possible several) recipients
28 in the CMS structure.
29 If cert is set to NULL all possible recipients are tried. This case
31 however is problematic. To thwart the MMA attack (Bleichenbacher's
32 attack on PKCS #1 v1.5 RSA padding) all recipients are tried whether
33 they succeed or not. If no recipient succeeds then a random symmetric
34 key is used to decrypt the content: this will typically output garbage
35 and may (but is not guaranteed to) ultimately return a padding error
36 only. If CMS_decrypt() just returned an error when all recipient
37 encrypted keys failed to decrypt an attacker could use this in a timing
38 attack. If the special flag CMS_DEBUG_DECRYPT is set then the above
39 behaviour is modified and an error is returned if no recipient
40 encrypted key can be decrypted without generating a random content
41 encryption key. Applications should use this flag with extreme caution
42 especially in automated gateways as it can leave them open to attack.
43 It is possible to determine the correct recipient key by other means
45 (for example looking them up in a database) and setting them in the CMS
46 structure in advance using the CMS utility functions such as
47 CMS_set1_pkey(). In this case both cert and pkey should be set to NULL.
48 To process KEKRecipientInfo types CMS_set1_key() or
50 CMS_RecipientInfo_set0_key() and CMS_ReceipientInfo_decrypt() should be
51 called before CMS_decrypt() and cert and pkey set to NULL.
52 The following flags can be passed in the flags parameter.
54 If the CMS_TEXT flag is set MIME headers for type text/plain are
56 deleted from the content. If the content is not of type text/plain then
57 an error is returned.
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60 CMS_decrypt() returns either 1 for success or 0 for failure. The error
61 can be obtained from ERR_get_error(3)
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64 The lack of single pass processing and the need to hold all data in
65 memory as mentioned in CMS_verify() also applies to CMS_decrypt().
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68 ERR_get_error(3), CMS_encrypt(3)
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71 CMS_decrypt() was added to OpenSSL 0.9.8
721.0.2o 2019-09-10 CMS_decrypt(3)