Only RSA keys are supported in PKCS#7 and envelopedData so the recipient
certificates supplied to this function must all contain RSA public keys, though
they do not have to be signed using the RSA algorithm.
EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use
because most clients will support it.
Some old export grade clients may only support weak encryption using 40 or 64
bit RC2. These can be used by passing EVP_rc2_40_cbc() and EVP_rc2_64_cbc()
The algorithm passed in the cipher parameter must support ASN1 encoding of
Many browsers implement a sign and encrypt option which is simply an S/MIME
envelopedData containing an S/MIME signed message. This can be readily produced
by storing the S/MIME signed message in a memory BIO and passing it to
The following flags can be passed in the flags parameter.
If the PKCS7_TEXT flag is set MIME headers for type text/plain are
prepended to the data.
Normally the supplied content is translated into MIME canonical format (as
required by the S/MIME specifications) if PKCS7_BINARY is set no translation
occurs. This option should be used if the supplied data is in binary format
otherwise the translation will corrupt it. If PKCS7_BINARY is set then
PKCS7_TEXT is ignored.
If the PKCS7_STREAM flag is set a partial PKCS7 structure is output
suitable for streaming I/O: no data is read from the BIO in.