1=pod
2
3=head1 NAME
4
5CMS_encrypt_ex, CMS_encrypt - create a CMS envelopedData structure
6
7=head1 SYNOPSIS
8
9 #include <openssl/cms.h>
10
11 CMS_ContentInfo *CMS_encrypt_ex(STACK_OF(X509) *certs, BIO *in,
12                                 const EVP_CIPHER *cipher, unsigned int flags,
13                                 OSSL_LIB_CTX *libctx, const char *propq);
14 CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in,
15                              const EVP_CIPHER *cipher, unsigned int flags);
16
17=head1 DESCRIPTION
18
19CMS_encrypt_ex() creates and returns a CMS EnvelopedData or
20AuthEnvelopedData structure. I<certs> is a list of recipient certificates.
21I<in> is the content to be encrypted. I<cipher> is the symmetric cipher to use.
22I<flags> is an optional set of flags. The library context I<libctx> and the
23property query I<propq> are used internally when retrieving algorithms from
24providers.
25
26Only certificates carrying RSA, Diffie-Hellman or EC keys are supported by this
27function.
28
29EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use
30because most clients will support it.
31
32The algorithm passed in the B<cipher> parameter must support ASN1 encoding of
33its parameters. If the cipher mode is GCM, then an AuthEnvelopedData structure
34containing MAC is used. Otherwise an EnvelopedData structure is used. Currently
35the AES variants with GCM mode are the only supported AEAD algorithms.
36
37Many browsers implement a "sign and encrypt" option which is simply an S/MIME
38envelopedData containing an S/MIME signed message. This can be readily produced
39by storing the S/MIME signed message in a memory BIO and passing it to
40CMS_encrypt().
41
42The following flags can be passed in the B<flags> parameter.
43
44If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
45prepended to the data.
46
47Normally the supplied content is translated into MIME canonical format (as
48required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
49occurs. This option should be used if the supplied data is in binary format
50otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
51B<CMS_TEXT> is ignored.
52
53OpenSSL will by default identify recipient certificates using issuer name
54and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
55identifier value instead. An error occurs if all recipient certificates do not
56have a subject key identifier extension.
57
58If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
59returned suitable for streaming I/O: no data is read from the BIO B<in>.
60
61If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
62returned to which additional recipients and attributes can be added before
63finalization.
64
65The data being encrypted is included in the CMS_ContentInfo structure, unless
66B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
67practice and is not supported by SMIME_write_CMS().
68
69If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
70B<not> complete and outputting its contents via a function that does not
71properly finalize the B<CMS_ContentInfo> structure will give unpredictable
72results.
73
74Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
75PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
76can be performed by obtaining the streaming ASN1 B<BIO> directly using
77BIO_new_CMS().
78
79The recipients specified in B<certs> use a CMS KeyTransRecipientInfo info
80structure. KEKRecipientInfo is also supported using the flag B<CMS_PARTIAL>
81and CMS_add0_recipient_key(). KEMRecipientInfo is also supported using the
82flag B<CMS_PARTIAL> and CMS_add1_recipient().
83
84The parameter B<certs> may be NULL if B<CMS_PARTIAL> is set and recipients
85are added later using CMS_add1_recipient() or CMS_add1_recipient_cert() with
86CMS_add0_recipient_key().
87
88CMS_encrypt() is similar to CMS_encrypt_ex() but uses default values
89of NULL for the library context I<libctx> and the property query I<propq>.
90
91=head1 RETURN VALUES
92
93CMS_encrypt_ex() and CMS_encrypt() return either a CMS_ContentInfo
94structure or NULL if an error occurred. The error can be obtained from
95ERR_get_error(3).
96
97=head1 SEE ALSO
98
99L<ERR_get_error(3)>, L<CMS_decrypt(3)>
100
101=head1 HISTORY
102
103The function CMS_encrypt_ex() was added in OpenSSL 3.0.
104
105The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
106
107=head1 COPYRIGHT
108
109Copyright 2008-2025 The OpenSSL Project Authors. All Rights Reserved.
110
111Licensed under the Apache License 2.0 (the "License").  You may not use
112this file except in compliance with the License.  You can obtain a copy
113in the file LICENSE in the source distribution or at
114L<https://www.openssl.org/source/license.html>.
115
116=cut
117