path: root/lib/libcrypto/man/CMS_decrypt.3

.\" $OpenBSD: CMS_decrypt.3,v 1.8 2019/11/02 15:39:46 schwarze Exp $
.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100
.\"
.\" This file is a derived work.
.\" The changes are covered by the following Copyright and license:
.\"
.\" Copyright (c) 2019 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\" The original file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2008, 2014 The OpenSSL Project.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 2 2019 $
.Dt CMS_DECRYPT 3
.Os
.Sh NAME
.Nm CMS_decrypt ,
.Nm CMS_decrypt_set1_pkey ,
.Nm CMS_decrypt_set1_key
.Nd decrypt content from a CMS EnvelopedData structure
.Sh SYNOPSIS
.In openssl/cms.h
.Ft int
.Fo CMS_decrypt
.Fa "CMS_ContentInfo *cms"
.Fa "EVP_PKEY *private_key"
.Fa "X509 *certificate"
.Fa "BIO *dcont"
.Fa "BIO *out"
.Fa "unsigned int flags"
.Fc
.Ft int
.Fo CMS_decrypt_set1_pkey
.Fa "CMS_ContentInfo *cms"
.Fa "EVP_PKEY *private_key"
.Fa "X509 *certificate"
.Fc
.Ft int
.Fo CMS_decrypt_set1_key
.Fa "CMS_ContentInfo *cms"
.Fa "unsigned char *symmetric_key"
.Fa "size_t keylen"
.Fa "const unsigned char *id"
.Fa "size_t idlen"
.Fc
.Sh DESCRIPTION
.Fn CMS_decrypt
extracts and decrypts the content from the CMS
.Vt EnvelopedData
structure
.Fa cms
using the
.Fa private_key
and the
.Fa certificate
of the recipient.
It writes the decrypted content to
.Fa out .
.Pp
In the rare case where the compressed content is detached, pass it in via
.Fa dcont .
For normal use, set
.Fa dcont
to
.Dv NULL .
.Pp
Although the recipient's
.Fa certificate
is not needed to decrypt the data, it is needed to locate the
appropriate (of possibly several) recipients in the CMS structure.
.Pp
If the
.Fa certificate
is set to
.Dv 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, 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
.Fn 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
.Dv CMS_DEBUG_DECRYPT
is set, the above behaviour is modified and an error
.Em is
returned if no recipient encrypted key can be decrypted
.Em 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.
.Pp
It is possible to determine the correct recipient key by other means
(for example by looking them up in a database) and setting them in the
.Fa cms
structure in advance using the CMS utility functions such as
.Fn CMS_decrypt_set1_pkey .
In this case both
.Fa certificate
and
.Fa private_key
should be set to
.Dv NULL
when calling
.Fn CMS_decrypt
later on.
.Pp
To process
.Vt KEKRecipientInfo
types,
.Fn CMS_decrypt_set1_key
or
.Xr CMS_RecipientInfo_set0_key 3
and
.Xr CMS_RecipientInfo_decrypt 3
should be called before
.Fn CMS_decrypt
and
.Fa certificate
and
.Fa private_key
set to
.Dv NULL
when calling
.Fn CMS_decrypt
later on.
.Pp
If the
.Dv CMS_TEXT
bit is set in
.Fa flags ,
MIME headers for type text/plain are deleted from the content.
If the content is not of type text/plain, an error occurs.
.Sh RETURN VALUES
.Fn CMS_decrypt ,
.Fn CMS_decrypt_set1_pkey ,
and
.Fn CMS_decrypt_set1_key
return 1 for success or 0 for failure.
The error can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr CMS_ContentInfo_new 3 ,
.Xr CMS_encrypt 3 ,
.Xr CMS_get0_RecipientInfos 3
.Sh STANDARDS
RFC 5652: Cryptographic Message Syntax (CMS)
.Bl -dash -compact -offset indent
.It
section 6.1: EnvelopedData Type
.It
section 6.2.3: KEKRecipientInfo Type
.El
.Sh HISTORY
.Fn CMS_decrypt ,
.Fn CMS_decrypt_set1_pkey ,
and
.Fn CMS_decrypt_set1_key
first appeared in OpenSSL 0.9.8h
and have been available since
.Ox 6.7 .
.Sh BUGS
The lack of single pass processing and the need to hold all data in
memory as mentioned in
.Xr CMS_verify 3
also applies to
.Fn CMS_decrypt .