CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, CMS_decrypt_set1_pkey,
CMS_decrypt_set1_password - decrypt content from a CMS envelopedData structure
#include <openssl/cms.h>
int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert,
BIO *dcont, BIO *out, unsigned int flags);
int CMS_decrypt_set1_pkey_and_peer(CMS_ContentInfo *cms,
EVP_PKEY *pk, X509 *cert, X509 *peer);
int CMS_decrypt_set1_pkey(CMS_ContentInfo *cms, EVP_PKEY *pk, X509 *cert);
int CMS_decrypt_set1_password(CMS_ContentInfo *cms,
unsigned char *pass, ossl_ssize_t passlen);
CMS_decrypt() extracts the decrypted content from a CMS EnvelopedData or
AuthEnvelopedData structure. It uses
CMS_decrypt_set1_pkey() to decrypt
the content with the recipient private key
pkey if
pkey is not
NULL. In this case, it is recommended to provide the associated certificate in
cert - see the NOTES below.
out is a BIO to write the content to
and
flags is an optional set of flags. If
pkey is NULL the
function assumes that decryption was already done (e.g., using
CMS_decrypt_set1_pkey() or
CMS_decrypt_set1_password()) and just
provides the content unless
cert,
dcont, and
out are NULL
as well. The
dcont parameter is used in the rare case where the
encrypted content is detached. It will normally be set to NULL.
CMS_decrypt_set1_pkey_and_peer() decrypts the CMS_ContentInfo structure
cms using the private key
pkey, the corresponding certificate
cert, which is recommended to be supplied but may be NULL, and the
(optional) originator certificate
peer. On success, it also records in
cms the decryption key
pkey, and this should be followed by
"CMS_decrypt(cms, NULL, NULL, dcont, out, flags)". This call
deallocates any decryption key stored in
cms.
CMS_decrypt_set1_pkey() is the same as
CMS_decrypt_set1_pkey_and_peer() with
peer being NULL.
CMS_decrypt_set1_password() decrypts the CMS_ContentInfo structure
cms using the secret
pass of length
passlen. On success,
it also records in
cms the decryption key used, and this should be
followed by "CMS_decrypt(cms, NULL, NULL, dcont, out, flags)". This
call deallocates any decryption key stored in
cms.
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(), or
use
CMS_decrypt_set1_password() if the recipient has a symmetric key.
In these cases both
cert and
pkey should be set to NULL.
To process KEKRecipientInfo types
CMS_set1_key() or
CMS_RecipientInfo_set0_key() and
CMS_RecipientInfo_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.
CMS_decrypt(),
CMS_decrypt_set1_pkey_and_peer(),
CMS_decrypt_set1_pkey(), and
CMS_decrypt_set1_password() return
either 1 for success or 0 for failure. The error can be obtained from
ERR_get_error(3).
The
set1_ part of these function names is misleading and should better
read:
with_.
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().
ERR_get_error(3),
CMS_encrypt(3)
CMS_decrypt_set1_pkey_and_peer() and
CMS_decrypt_set1_password()
were added in OpenSSL 3.0.
Copyright 2008-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at
<
https://www.openssl.org/source/license.html>.