CMS_decrypt - decrypt content from a CMS envelopedData structure
int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert, BIO *dcont, BIO *out, unsigned int flags);
The dcont parameter is used in the rare case where the encrypted content is detached. It will normally be set to NULL.
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
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
To process KEKRecipientInfo types
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.
The lack of single pass processing and the need to hold all data in memory
as mentioned in