CMS_encrypt (3)

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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 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 keys are supported so the recipient certificates supplied to this function must all contain public keys, though they do not have to be signed using the algorithm.

EVP_des_ede3_cbc() (triple

) is the algorithm of choice for S/MIME use because most clients will support it.

The algorithm passed in the cipher parameter must support

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

and passing it to CMS_encrypt().

The following flags can be passed in the flags parameter.

If the

flag is set headers for type text/plain are prepended to the data.

Normally the supplied content is translated into

canonical format (as required by the S/MIME specifications) if 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 is set then is ignored.

OpenSSL will by default identify recipient certificates using issuer name and serial number. If

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

flag is set a partial CMS_ContentInfo structure is returned suitable for streaming I/O: no data is read from the in.

If the

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

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 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

directly using BIO_new_CMS().

The recipients specified in certs use a

KeyTransRecipientInfo info structure. KEKRecipientInfo is also supported using the flag and CMS_add0_recipient_key().

The parameter certs may be

if 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 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 flag was first supported in OpenSSL 1.0.0.