80 lines
2.9 KiB
Plaintext
80 lines
2.9 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
CMS_decrypt - decrypt content from a CMS envelopedData structure
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/cms.h>
|
|
|
|
int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData
|
|
structure. B<pkey> is the private key of the recipient, B<cert> is the
|
|
recipient's certificate, B<out> is a BIO to write the content to and
|
|
B<flags> is an optional set of flags.
|
|
|
|
The B<dcont> parameter is used in the rare case where the encrypted content
|
|
is detached. It will normally be set to NULL.
|
|
|
|
=head1 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 B<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 B<CMS_DEBUG_DECRYPT> is set
|
|
then the above behaviour is modified and an error B<is> returned if no
|
|
recipient encrypted key can be decrypted B<without> generating a random
|
|
content encryption key. Applications should use this flag with
|
|
B<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 B<cert> and B<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
|
|
B<cert> and B<pkey> set to NULL.
|
|
|
|
The following flags can be passed in the B<flags> parameter.
|
|
|
|
If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
|
|
from the content. If the content is not of type B<text/plain> then an error is
|
|
returned.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
CMS_decrypt() returns either 1 for success or 0 for failure.
|
|
The error can be obtained from ERR_get_error(3)
|
|
|
|
=head1 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().
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_encrypt(3)|CMS_encrypt(3)>
|
|
|
|
=head1 HISTORY
|
|
|
|
CMS_decrypt() was added to OpenSSL 0.9.8
|
|
|
|
=cut
|