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Commit	Line	Data
	1	=pod
	2
	3	=head1 NAME
	4
	5	CMS_decrypt - decrypt content from a CMS envelopedData structure
	6
	7	=head1 SYNOPSIS
	8
	9	#include <openssl/cms.h>
	10
	11	int CMS_decrypt(CMS_ContentInfo cms, EVP_PKEY pkey, X509 cert, BIO dcont, BIO *out, unsigned int flags);
	12
	13	=head1 DESCRIPTION
	14
	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.
	19
	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.
	22
	23	=head1 NOTES
	24
	25	OpenSSL_add_all_algorithms() (or equivalent) should be called before using this
	26	function or errors about unknown algorithms will occur.
	27
	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
	30	structure.
	31
	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
	44	open to attack.
	45
	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.
	50
	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.
	54
	55	The following flags can be passed in the B<flags> parameter.
	56
	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
	59	returned.
	60
	61	=head1 RETURN VALUES
	62
	63	CMS_decrypt() returns either 1 for success or 0 for failure.
	64	The error can be obtained from ERR_get_error(3)
	65
	66	=head1 BUGS
	67
	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().
	70
	71	=head1 SEE ALSO
	72
	73	L<ERR_get_error(3)\|ERR_get_error(3)>, L<CMS_encrypt(3)\|CMS_encrypt(3)>
	74
	75	=head1 HISTORY
	76
	77	CMS_decrypt() was added to OpenSSL 0.9.8
	78
	79	=cut