=pod

=head1 NAME

CMS_add1_recipient, CMS_add1_recipient_cert, CMS_add0_recipient_key - add recipients to a CMS enveloped data structure

=head1 SYNOPSIS

 #include <openssl/cms.h>

 CMS_RecipientInfo *CMS_add1_recipient(CMS_ContentInfo *cms, X509 *recip,
                                       EVP_PKEY *originatorPrivKey,
                                       X509 *originator, unsigned int flags);

 CMS_RecipientInfo *CMS_add1_recipient_cert(CMS_ContentInfo *cms,
                                            X509 *recip, unsigned int flags);

 CMS_RecipientInfo *CMS_add0_recipient_key(CMS_ContentInfo *cms, int nid,
                                           unsigned char *key, size_t keylen,
                                           unsigned char *id, size_t idlen,
                                           ASN1_GENERALIZEDTIME *date,
                                           ASN1_OBJECT *otherTypeId,
                                           ASN1_TYPE *otherType);

=head1 DESCRIPTION

CMS_add1_recipient() adds recipient B<recip> and provides the originator pkey
B<originatorPrivKey> and originator certificate B<originator> to CMS_ContentInfo.
The originator-related fields are relevant only in case when the keyAgreement
method of providing of the shared key is in use.

CMS_add1_recipient_cert() adds recipient B<recip> to CMS_ContentInfo enveloped
data structure B<cms> as a KeyTransRecipientInfo or KEMRecipientInfo structure,
or as a KeyAgreeRecipientInfo structure with an ephemeral key.

CMS_add0_recipient_key() adds symmetric key B<key> of length B<keylen> using
wrapping algorithm B<nid>, identifier B<id> of length B<idlen> and optional
values B<date>, B<otherTypeId> and B<otherType> to CMS_ContentInfo enveloped
data structure B<cms> as a KEKRecipientInfo structure.

The CMS_ContentInfo structure should be obtained from an initial call to
CMS_encrypt() with the flag B<CMS_PARTIAL> set.

=head1 NOTES

The main purpose of this function is to provide finer control over a CMS
enveloped data structure where the simpler CMS_encrypt() function defaults are
not appropriate. For example if one or more KEKRecipientInfo structures
need to be added. New attributes can also be added using the returned
CMS_RecipientInfo structure and the CMS attribute utility functions.

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

Currently only AES based key wrapping algorithms are supported for B<nid>,
specifically: NID_id_aes128_wrap, NID_id_aes192_wrap and NID_id_aes256_wrap.
If B<nid> is set to B<NID_undef> then an AES wrap algorithm will be used
consistent with B<keylen>.

=head1 RETURN VALUES

CMS_add1_recipient_cert() and CMS_add0_recipient_key() return an internal
pointer to the CMS_RecipientInfo structure just added or NULL if an error
occurs.

=head1 SEE ALSO

L<ERR_get_error(3)>, L<CMS_decrypt(3)>,
L<CMS_final(3)>,

=head1 HISTORY

B<CMS_add1_recipient_cert> and B<CMS_add0_recipient_key> were added in
OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2008-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
