NAME¶
CMS_encrypt - create a CMS envelopedData structure
SYNOPSIS¶
#include <openssl/cms.h>
CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in, const EVP_CIPHER *cipher, unsigned int flags);
DESCRIPTION¶
CMS_encrypt() creates and returns a CMS EnvelopedData structure.
certs is a list of recipient certificates.
in is the content to
be encrypted.
cipher is the symmetric cipher to use.
flags is an
optional set of flags.
NOTES¶
Only certificates carrying RSA keys are supported 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.
The algorithm passed in the
cipher parameter must support ASN1 encoding
of its parameters.
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
CMS_encrypt().
The following flags can be passed in the
flags parameter.
If the
CMS_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
CMS_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
CMS_BINARY
is set then
CMS_TEXT is ignored.
OpenSSL will by default identify recipient certificates using issuer name and
serial number. If
CMS_USE_KEYID is set it will use the subject key
identifier value instead. An error occurs if all recipient certificates do not
have a subject key identifier extension.
If the
CMS_STREAM flag is set a partial
CMS_ContentInfo structure
is returned suitable for streaming I/O: no data is read from the BIO
in.
If the
CMS_PARTIAL flag is set a partial
CMS_ContentInfo structure
is returned to which additional recipients and attributes can be added before
finalization.
The data being encrypted is included in the CMS_ContentInfo structure, unless
CMS_DETACHED is set in which case it is omitted. This is rarely used in
practice and is not supported by
SMIME_write_CMS().
NOTES¶
If the flag
CMS_STREAM is set the returned
CMS_ContentInfo
structure is
not complete and outputting its contents via a function
that does not properly finalize the
CMS_ContentInfo structure will give
unpredictable results.
Several functions including
SMIME_write_CMS(),
i2d_CMS_bio_stream(),
PEM_write_bio_CMS_stream() finalize the
structure. Alternatively finalization can be performed by obtaining the
streaming ASN1
BIO directly using
BIO_new_CMS().
The recipients specified in
certs use a CMS KeyTransRecipientInfo info
structure. KEKRecipientInfo is also supported using the flag
CMS_PARTIAL and
CMS_add0_recipient_key().
The parameter
certs may be NULL if
CMS_PARTIAL is set and
recipients added later using
CMS_add1_recipient_cert() or
CMS_add0_recipient_key().
RETURN VALUES¶
CMS_encrypt() returns either a CMS_ContentInfo structure or NULL if an
error occurred. The error can be obtained from
ERR_get_error(3).
SEE ALSO¶
ERR_get_error(3),
CMS_decrypt(3)
HISTORY¶
CMS_decrypt() was added to OpenSSL 0.9.8 The
CMS_STREAM flag was
first supported in OpenSSL 1.0.0.