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CMS_decrypt(3) OpenSSL CMS_decrypt(3)
NAME
CMS_decrypt - decrypt content from a CMS envelopedData structure
SYNOPSIS
#include <openssl/cms.h>
int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
DESCRIPTION
CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData structure. pkey
is the private key of the recipient, cert is the recipient's certificate, out is a BIO to
write the content to and flags is an optional set of flags.
The dcont parameter is used in the rare case where the encrypted content is detached. It
will normally be set to NULL.
NOTES
OpenSSL_add_all_algorithms() (or equivalent) should be called before using this function
or errors about unknown algorithms will occur.
Although the recipients certificate is not needed to decrypt the data it is needed to
locate the appropriate (of possible several) recipients in the CMS structure.
If cert is set to NULL all possible recipients are tried. This case however is
problematic. To thwart the MMA attack (Bleichenbacher's attack on PKCS #1 v1.5 RSA
padding) all recipients are tried whether they succeed or not. If no recipient succeeds
then a random symmetric key is used to decrypt the content: this will typically output
garbage and may (but is not guaranteed to) ultimately return a padding error only. If
CMS_decrypt() just returned an error when all recipient encrypted keys failed to decrypt
an attacker could use this in a timing attack. If the special flag CMS_DEBUG_DECRYPT is
set then the above behaviour is modified and an error is returned if no recipient
encrypted key can be decrypted without generating a random content encryption key.
Applications should use this flag with extreme caution especially in automated gateways as
it can leave them open to attack.
It is possible to determine the correct recipient key by other means (for example looking
them up in a database) and setting them in the CMS structure in advance using the CMS
utility functions such as CMS_set1_pkey(). In this case both cert and pkey should be set
to NULL.
To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key() and
CMS_ReceipientInfo_decrypt() should be called before CMS_decrypt() and cert and pkey set
to NULL.
The following flags can be passed in the flags parameter.
If the CMS_TEXT flag is set MIME headers for type text/plain are deleted from the content.
If the content is not of type text/plain then an error is returned.
RETURN VALUES
CMS_decrypt() returns either 1 for success or 0 for failure. The error can be obtained
from ERR_get_error(3)
BUGS
The lack of single pass processing and the need to hold all data in memory as mentioned in
CMS_verify() also applies to CMS_decrypt().
SEE ALSO
ERR_get_error(3), CMS_encrypt(3)
HISTORY
CMS_decrypt() was added to OpenSSL 0.9.8
1.0.2k 2017-01-26 CMS_decrypt(3)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-27 02:38 @18.217.6.114 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)