1=pod 2 3=head1 NAME 4 5CMS_sign - create a CMS SignedData structure 6 7=head1 SYNOPSIS 8 9 #include <openssl/cms.h> 10 11 CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, 12 BIO *data, unsigned int flags); 13 14=head1 DESCRIPTION 15 16CMS_sign() creates and returns a CMS SignedData structure. B<signcert> is 17the certificate to sign with, B<pkey> is the corresponding private key. 18B<certs> is an optional additional set of certificates to include in the CMS 19structure (for example any intermediate CAs in the chain). Any or all of 20these parameters can be B<NULL>, see B<NOTES> below. 21 22The data to be signed is read from BIO B<data>. 23 24B<flags> is an optional set of flags. 25 26=head1 NOTES 27 28Any of the following flags (ored together) can be passed in the B<flags> 29parameter. 30 31Many S/MIME clients expect the signed content to include valid MIME headers. If 32the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are prepended 33to the data. 34 35If B<CMS_NOCERTS> is set the signer's certificate will not be included in the 36CMS_ContentInfo structure, the signer's certificate must still be supplied in 37the B<signcert> parameter though. This can reduce the size of the signature if 38the signers certificate can be obtained by other means: for example a 39previously signed message. 40 41The data being signed is included in the CMS_ContentInfo structure, unless 42B<CMS_DETACHED> is set in which case it is omitted. This is used for 43CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed 44messages for example. 45 46Normally the supplied content is translated into MIME canonical format (as 47required by the S/MIME specifications) if B<CMS_BINARY> is set no translation 48occurs. This option should be used if the supplied data is in binary format 49otherwise the translation will corrupt it. 50 51The SignedData structure includes several CMS signedAttributes including the 52signing time, the CMS content type and the supported list of ciphers in an 53SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes 54will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are 55omitted. 56 57If present the SMIMECapabilities attribute indicates support for the following 58algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192 59bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. 60If any of these algorithms is not available then it will not be included: for example the GOST algorithms will not be included if the GOST ENGINE is 61not loaded. 62 63OpenSSL will by default identify signing certificates using issuer name 64and serial number. If B<CMS_USE_KEYID> is set it will use the subject key 65identifier value instead. An error occurs if the signing certificate does not 66have a subject key identifier extension. 67 68If the flags B<CMS_STREAM> is set then the returned B<CMS_ContentInfo> 69structure is just initialized ready to perform the signing operation. The 70signing is however B<not> performed and the data to be signed is not read from 71the B<data> parameter. Signing is deferred until after the data has been 72written. In this way data can be signed in a single pass. 73 74If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is 75output to which additional signers and capabilities can be added before 76finalization. 77 78If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is 79B<not> complete and outputting its contents via a function that does not 80properly finalize the B<CMS_ContentInfo> structure will give unpredictable 81results. 82 83Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(), 84PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization 85can be performed by obtaining the streaming ASN1 B<BIO> directly using 86BIO_new_CMS(). 87 88If a signer is specified it will use the default digest for the signing 89algorithm. This is B<SHA1> for both RSA and DSA keys. 90 91If B<signcert> and B<pkey> are NULL then a certificates only CMS structure is 92output. 93 94The function CMS_sign() is a basic CMS signing function whose output will be 95suitable for many purposes. For finer control of the output format the 96B<certs>, B<signcert> and B<pkey> parameters can all be B<NULL> and the 97B<CMS_PARTIAL> flag set. Then one or more signers can be added using the 98function CMS_sign_add1_signer(), non default digests can be used and custom 99attributes added. CMS_final() must then be called to finalize the 100structure if streaming is not enabled. 101 102=head1 BUGS 103 104Some attributes such as counter signatures are not supported. 105 106=head1 RETURN VALUES 107 108CMS_sign() returns either a valid CMS_ContentInfo structure or NULL if an error 109occurred. The error can be obtained from ERR_get_error(3). 110 111=head1 SEE ALSO 112 113L<ERR_get_error(3)>, L<CMS_verify(3)> 114 115=head1 HISTORY 116 117The B<CMS_STREAM> flag is only supported for detached data in OpenSSL 0.9.8, 118it is supported for embedded data in OpenSSL 1.0.0 and later. 119 120=head1 COPYRIGHT 121 122Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved. 123 124Licensed under the OpenSSL license (the "License"). You may not use 125this file except in compliance with the License. You can obtain a copy 126in the file LICENSE in the source distribution or at 127L<https://www.openssl.org/source/license.html>. 128 129=cut 130