CMS_encrypt.pod revision 337982 
1=pod
2
3=head1 NAME
4
5 CMS_encrypt - create a CMS envelopedData structure
6
7=head1 SYNOPSIS
8
9 #include <openssl/cms.h>
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11 CMS_ContentInfo *CMS_encrypt(STACK_OF(X509) *certs, BIO *in, const EVP_CIPHER *cipher, unsigned int flags);
12
13=head1 DESCRIPTION
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15CMS_encrypt() creates and returns a CMS EnvelopedData structure. B<certs>
16is a list of recipient certificates. B<in> is the content to be encrypted.
17B<cipher> is the symmetric cipher to use. B<flags> is an optional set of flags.
18
19=head1 NOTES
20
21Only certificates carrying RSA, Diffie-Hellman or EC keys are supported by this
22function.
23
24EVP_des_ede3_cbc() (triple DES) is the algorithm of choice for S/MIME use
25because most clients will support it.
26
27The algorithm passed in the B<cipher> parameter must support ASN1 encoding of
28its parameters. 
29
30Many browsers implement a "sign and encrypt" option which is simply an S/MIME
31envelopedData containing an S/MIME signed message. This can be readily produced
32by storing the S/MIME signed message in a memory BIO and passing it to
33CMS_encrypt().
34
35The following flags can be passed in the B<flags> parameter.
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37If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
38prepended to the data.
39
40Normally the supplied content is translated into MIME canonical format (as
41required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
42occurs. This option should be used if the supplied data is in binary format
43otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
44B<CMS_TEXT> is ignored.
45
46OpenSSL will by default identify recipient certificates using issuer name
47and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
48identifier value instead. An error occurs if all recipient certificates do not
49have a subject key identifier extension.
50
51If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
52returned suitable for streaming I/O: no data is read from the BIO B<in>.
53
54If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
55returned to which additional recipients and attributes can be added before
56finalization.
57
58The data being encrypted is included in the CMS_ContentInfo structure, unless
59B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
60practice and is not supported by SMIME_write_CMS().
61
62=head1 NOTES
63
64If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
65B<not> complete and outputting its contents via a function that does not
66properly finalize the B<CMS_ContentInfo> structure will give unpredictable
67results.
68
69Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
70PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
71can be performed by obtaining the streaming ASN1 B<BIO> directly using
72BIO_new_CMS().
73
74The recipients specified in B<certs> use a CMS KeyTransRecipientInfo info
75structure. KEKRecipientInfo is also supported using the flag B<CMS_PARTIAL>
76and CMS_add0_recipient_key().
77
78The parameter B<certs> may be NULL if B<CMS_PARTIAL> is set and recipients
79added later using CMS_add1_recipient_cert() or CMS_add0_recipient_key().
80
81=head1 RETURN VALUES
82
83CMS_encrypt() returns either a CMS_ContentInfo structure or NULL if an error
84occurred. The error can be obtained from ERR_get_error(3).
85
86=head1 SEE ALSO
87
88L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_decrypt(3)|CMS_decrypt(3)>
89
90=head1 HISTORY
91
92CMS_decrypt() was added to OpenSSL 0.9.8
93The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
94
95=cut
96