bionic (3) CMS_decrypt.3ssl.gz

Provided by: libssl-doc_1.1.1-1ubuntu2.1~18.04.23_all bug

NAME
       CMS_decrypt - 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);


DESCRIPTION
       CMS_decrypt() extracts and decrypts the content from a CMS EnvelopedData 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.


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)


       Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (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>.