CMS_DECRYPT(3ossl) OpenSSL CMS_DECRYPT(3ossl)
NAME
CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, CMS_decrypt_set1_pkey,
CMS_decrypt_set1_password - decrypt content from a CMS envelopedData
structure
SYNOPSIS
#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);
DESCRIPTION
CMS_decrypt(3) 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, the associated certificate is recommended to
provide 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 but may be NULL, and the (optional) originator
certificate peer. On success, it also records in cms the decryption
key pkey, and then 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 then should be followed by
"CMS_decrypt(cms, NULL, NULL, dcont, out, flags)". This call
deallocates any decryption key stored in cms.
NOTES
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(3) 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(3) 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.
RETURN VALUES
CMS_decrypt(3), 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).
BUGS
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_decrypt(3).
SEE ALSO
ERR_get_error(3), CMS_encrypt(3)
HISTORY
CMS_decrypt_set1_pkey_and_peer() and CMS_decrypt_set1_password() were
added in OpenSSL 3.0.
COPYRIGHT
Copyright 2008-2020 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>.
3.3.2 2024-09-04 CMS_DECRYPT(3ossl)
openssl 3.3.2 - Generated Sat Sep 7 14:05:23 CDT 2024