a528d4f0a9
If something was "present in all versions" of SSLeay, or if it was added to a version of SSLeay (and therefore predates OpenSSL), remove mention of it. Documentation history now starts with OpenSSL. Remove mention of all history before OpenSSL 0.9.8, inclusive. Remove all AUTHOR sections. Reviewed-by: Tim Hudson <tjh@openssl.org>
75 lines
2.8 KiB
Text
75 lines
2.8 KiB
Text
=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)>, L<CMS_encrypt(3)>
|
|
|
|
=cut
|