CMS_DECRYPT(3SSL) OpenSSL CMS_DECRYPT(3SSL)
NAME
CMS_decrypt, CMS_decrypt_set1_pkey_and_peer, CMS_decrypt_set1_pkey -
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);
DESCRIPTION
CMS_decrypt() extracts and decrypts the content from a CMS
EnvelopedData or AuthEnvelopedData structure. pkey is the private key
of the recipient, cert is the recipient's certificate, out is a BIO to
write the content to and flags is an optional set of flags.
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() associates the private key pkey, the
corresponding certificate cert and the originator certificate peer with
the CMS_ContentInfo structure cms.
CMS_decrypt_set1_pkey() associates the private key pkey, corresponding
certificate cert with the CMS_ContentInfo structure 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() 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(). In this case 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.
RETURN VALUES
CMS_decrypt() returns either 1 for success or 0 for failure. The error
can be obtained from ERR_get_error(3)
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().
SEE ALSO
ERR_get_error(3), CMS_encrypt(3)
HISTORY
CMS_decrypt_set1_pkey_and_peer was 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>.
3.0.2 2024-08-20 CMS_DECRYPT(3SSL)
Generated by dwww version 1.14 on Thu Jan 23 09:24:33 CET 2025.