=pod

=head1 NAME

CMS_get0_RecipientInfos, CMS_RecipientInfo_type,
CMS_RecipientInfo_ktri_get0_signer_id, CMS_RecipientInfo_ktri_cert_cmp,
CMS_RecipientInfo_set0_pkey, CMS_RecipientInfo_kekri_get0_id,
CMS_RecipientInfo_kari_set0_pkey_and_peer,
CMS_RecipientInfo_kari_set0_pkey, CMS_RecipientInfo_kari_get0_ctx,
CMS_RecipientInfo_kekri_id_cmp, CMS_RecipientInfo_set0_key,
CMS_RecipientInfo_kemri_cert_cmp, CMS_RecipientInfo_kemri_set0_pkey,
CMS_RecipientInfo_kemri_get0_ctx, CMS_RecipientInfo_kemri_get0_kdf_alg,
CMS_RecipientInfo_kemri_set_ukm, CMS_RecipientInfo_decrypt,
CMS_RecipientInfo_encrypt
- CMS envelopedData RecipientInfo routines

=head1 SYNOPSIS

 #include <openssl/cms.h>

 STACK_OF(CMS_RecipientInfo) *CMS_get0_RecipientInfos(CMS_ContentInfo *cms);
 int CMS_RecipientInfo_type(CMS_RecipientInfo *ri);

 int CMS_RecipientInfo_ktri_get0_signer_id(CMS_RecipientInfo *ri,
                                           ASN1_OCTET_STRING **keyid,
                                           X509_NAME **issuer,
                                           ASN1_INTEGER **sno);
 int CMS_RecipientInfo_ktri_cert_cmp(CMS_RecipientInfo *ri, X509 *cert);
 int CMS_RecipientInfo_set0_pkey(CMS_RecipientInfo *ri, EVP_PKEY *pkey);
 int CMS_RecipientInfo_kari_set0_pkey_and_peer(CMS_RecipientInfo *ri,
                                               EVP_PKEY *pk, X509 *peer);
 int CMS_RecipientInfo_kari_set0_pkey(CMS_RecipientInfo *ri, EVP_PKEY *pk);
 EVP_CIPHER_CTX *CMS_RecipientInfo_kari_get0_ctx(CMS_RecipientInfo *ri);
 int CMS_RecipientInfo_kekri_get0_id(CMS_RecipientInfo *ri, X509_ALGOR **palg,
                                     ASN1_OCTET_STRING **pid,
                                     ASN1_GENERALIZEDTIME **pdate,
                                     ASN1_OBJECT **potherid,
                                     ASN1_TYPE **pothertype);
 int CMS_RecipientInfo_kekri_id_cmp(CMS_RecipientInfo *ri,
                                    const unsigned char *id, size_t idlen);
 int CMS_RecipientInfo_set0_key(CMS_RecipientInfo *ri,
                                unsigned char *key, size_t keylen);
 int CMS_RecipientInfo_kemri_cert_cmp(CMS_RecipientInfo *ri, X509 *cert);
 int CMS_RecipientInfo_kemri_set0_pkey(CMS_RecipientInfo *ri, EVP_PKEY *pk);
 EVP_CIPHER_CTX *CMS_RecipientInfo_kemri_get0_ctx(CMS_RecipientInfo *ri);
 X509_ALGOR *CMS_RecipientInfo_kemri_get0_kdf_alg(CMS_RecipientInfo *ri);
 int CMS_RecipientInfo_kemri_set_ukm(CMS_RecipientInfo *ri,
                                     const unsigned char *ukm,
                                     int ukmLength);

 int CMS_RecipientInfo_decrypt(CMS_ContentInfo *cms, CMS_RecipientInfo *ri);
 int CMS_RecipientInfo_encrypt(CMS_ContentInfo *cms, CMS_RecipientInfo *ri);

=head1 DESCRIPTION

The function CMS_get0_RecipientInfos() returns all the CMS_RecipientInfo
structures associated with a CMS EnvelopedData structure.

CMS_RecipientInfo_type() returns the type of CMS_RecipientInfo structure B<ri>.
It will currently return CMS_RECIPINFO_TRANS, CMS_RECIPINFO_AGREE,
CMS_RECIPINFO_KEK, CMS_RECIPINFO_PASS, CMS_RECIPINFO_KEM, or
CMS_RECIPINFO_OTHER.

CMS_RecipientInfo_ktri_get0_signer_id() retrieves the certificate recipient
identifier associated with a specific CMS_RecipientInfo structure B<ri>, which
must be of type CMS_RECIPINFO_TRANS. Either the keyidentifier will be set in
B<keyid> or B<both> issuer name and serial number in B<issuer> and B<sno>.

CMS_RecipientInfo_ktri_cert_cmp() compares the certificate B<cert> against the
CMS_RecipientInfo structure B<ri>, which must be of type CMS_RECIPINFO_TRANS.
It returns zero if the comparison is successful and non zero if not.

CMS_RecipientInfo_set0_pkey() associates the private key B<pkey> with
the CMS_RecipientInfo structure B<ri>, which must be of type
CMS_RECIPINFO_TRANS.

CMS_RecipientInfo_kari_set0_pkey_and_peer() associates the private key B<pkey>
and peer certificate B<peer> with the CMS_RecipientInfo structure B<ri>, which
must be of type CMS_RECIPINFO_AGREE.

CMS_RecipientInfo_kari_set0_pkey() associates the private key B<pkey> with the
CMS_RecipientInfo structure B<ri>, which must be of type CMS_RECIPINFO_AGREE.

CMS_RecipientInfo_kari_get0_ctx() returns the EVP_CIPHER_CTX for the key
encryption key, allowing the caller to specify the key wrap cipher.  The
CMS_RecipientInfo structure B<ri> must be of type CMS_RECIPINFO_AGREE.

CMS_RecipientInfo_kekri_get0_id() retrieves the key information from the
CMS_RecipientInfo structure B<ri> which must be of type CMS_RECIPINFO_KEK.  Any
of the remaining parameters can be NULL if the application is not interested in
the value of a field. Where a field is optional and absent NULL will be written
to the corresponding parameter. The keyEncryptionAlgorithm field is written to
B<palg>, the B<keyIdentifier> field is written to B<pid>, the B<date> field if
present is written to B<pdate>, if the B<other> field is present the components
B<keyAttrId> and B<keyAttr> are written to parameters B<potherid> and
B<pothertype>.

CMS_RecipientInfo_kekri_id_cmp() compares the ID in the B<id> and B<idlen>
parameters against the B<keyIdentifier> CMS_RecipientInfo structure B<ri>,
which must be of type CMS_RECIPINFO_KEK.  It returns zero if the comparison is
successful and non zero if not.

CMS_RecipientInfo_set0_key() associates the symmetric key B<key> of length
B<keylen> with the CMS_RecipientInfo structure B<ri>, which must be of type
CMS_RECIPINFO_KEK.

CMS_RecipientInfo_kemri_cert_cmp() compares the certificate B<cert> against the
CMS_RecipientInfo structure B<ri>, which must be of type CMS_RECIPINFO_KEM.
It returns zero if the comparison is successful and non zero if not.

CMS_RecipientInfo_kemri_set0_pkey() associates the private key B<pkey> with the
CMS_RecipientInfo structure B<ri>, which must be of type CMS_RECIPINFO_KEM.

CMS_RecipientInfo_kemri_get0_ctx() returns the EVP_CIPHER_CTX for the key
encryption key, allowing the caller to specify the key wrap cipher.  The
CMS_RecipientInfo structure B<ri> must be of type CMS_RECIPINFO_KEM.

CMS_RecipientInfo_kemri_get0_kdf_alg() returns the X509_ALGOR for the
RecipientInfo's KDF, allowing the caller to specify the KDF algorithm.  The
CMS_RecipientInfo structure B<ri> must be of type CMS_RECIPINFO_KEM. If the
caller doesn't specify a KDF algorithm, B<HKDF-SHA256> will be used.

CMS_RecipientInfo_kemri_set_ukm() sets the RecipientInfo's optional user
keying material (UKM).  The UKM is encoded, along with other information, into
the B<OSSL_KDF_PARAM_INFO> parameter of the RecipientInfo's KDF. The
CMS_RecipientInfo structure B<ri> must be of type CMS_RECIPINFO_KEM.

CMS_RecipientInfo_decrypt() attempts to decrypt CMS_RecipientInfo structure
B<ri> in structure B<cms>. A key must have been associated with the structure
first.

CMS_RecipientInfo_encrypt() attempts to encrypt CMS_RecipientInfo structure
B<ri> in structure B<cms>. A key must have been associated with the structure
first and the content encryption key must be available: for example by a
previous call to CMS_RecipientInfo_decrypt().

=head1 NOTES

The main purpose of these functions is to enable an application to lookup
recipient keys using any appropriate technique when the simpler method
of CMS_decrypt() is not appropriate.

In typical usage and application will retrieve all CMS_RecipientInfo structures
using CMS_get0_RecipientInfos() and check the type of each using
CMS_RecipientInfo_type(). Depending on the type the CMS_RecipientInfo structure
can be ignored or its key identifier data retrieved using an appropriate
function. Then if the corresponding secret or private key can be obtained by
any appropriate means it can then associated with the structure and
CMS_RecipientInfo_decrypt() called. If successful CMS_decrypt() can be called
with a NULL key to decrypt the enveloped content.

The CMS_RecipientInfo_encrypt() can be used to add a new recipient to an
existing enveloped data structure. Typically an application will first decrypt
an appropriate CMS_RecipientInfo structure to make the content encrypt key
available, it will then add a new recipient using a function such as
CMS_add1_recipient_cert() and finally encrypt the content encryption key
using CMS_RecipientInfo_encrypt().

=head1 RETURN VALUES

CMS_get0_RecipientInfos() returns all CMS_RecipientInfo structures, or NULL if
an error occurs.

CMS_RecipientInfo_ktri_get0_signer_id(), CMS_RecipientInfo_set0_pkey(),
CMS_RecipientInfo_kekri_get0_id(), CMS_RecipientInfo_set0_key(),
CMS_RecipientInfo_kemri_set0_pkey(), CMS_RecipientInfo_kemri_set_ukm(),
CMS_RecipientInfo_decrypt() and CMS_RecipientInfo_encrypt() return 1 for
success or 0 if an error occurs.

CMS_RecipientInfo_ktri_cert_cmp(), CMS_RecipientInfo_kemri_cert_cmp() and
CMS_RecipientInfo_kekri_cmp() return 0 for a successful comparison and non zero
otherwise.

CMS_RecipientInfo_kemri_get0_ctx() and CMS_RecipientInfo_kari_get0_ctx return
the RecipientInfo's EVP_CIPHER_CTX or NULL if an error occurred.

CMS_RecipientInfo_kemri_get0_kdf_alg() returns the RecipientInfo's KDF's
X509_ALGOR or NULL if an error occurred.

Any error can be obtained from L<ERR_get_error(3)>.

=head1 SEE ALSO

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

=head1 HISTORY

B<CMS_RecipientInfo_kari_set0_pkey_and_peer> and B<CMS_RecipientInfo_kari_set0_pkey>
were added in OpenSSL 3.0.

B<CMS_RecipientInfo_kemri_cert_cmp>, B<CMS_RecipientInfo_kemri_set0_pkey>,
B<CMS_RecipientInfo_kemri_get0_ctx>, B<CMS_RecipientInfo_kemri_get0_kdf_alg>
and B<CMS_RecipientInfo_kemri_set_ukm> were added in OpenSSL 3.6.

=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
