CMS_decrypt(3)

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 Enveloped-
       Data 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 con-
       tent is detached. It will normally be set to NULL.

NOTES

       OpenSSL_add_all_algorithms() (or equivalent) should be called before
       using this function or errors about unknown algorithms will occur.

       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 be-
       haviour 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_Recipi-
       entInfo_set0_key() and CMS_ReceipientInfo_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() was added to OpenSSL 0.9.8

1.0.2t                            2019-09-10                    CMS_decrypt(3)