CMS_sign(3)                  OpenSSL                  CMS_sign(3)


      CMS_sign - create a CMS SignedData structure


      #include <openssl/cms.h>

      CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, unsigned int flags);


     CMS_sign() creates and returns a CMS SignedData structure.
     signcert is the certificate to sign with, pkey is the
     corresponding private key.  certs is an optional additional
     set of certificates to include in the CMS structure (for
     example any intermediate CAs in the chain). Any or all of
     these parameters can be NULL, see NOTES below.

     The data to be signed is read from BIO data.

     flags is an optional set of flags.


     Any of the following flags (ored together) can be passed in
     the flags parameter.

     Many S/MIME clients expect the signed content to include
     valid MIME headers. If the CMS_TEXT flag is set MIME headers
     for type text/plain are prepended to the data.

     If CMS_NOCERTS is set the signer's certificate will not be
     included in the CMS_ContentInfo structure, the signer's
     certificate must still be supplied in the signcert parameter
     though. This can reduce the size of the signature if the
     signers certificate can be obtained by other means: for
     example a previously signed message.

     The data being signed is included in the CMS_ContentInfo
     structure, unless CMS_DETACHED is set in which case it is
     omitted. This is used for CMS_ContentInfo detached
     signatures which are used in S/MIME plaintext signed
     messages for example.

     Normally the supplied content is translated into MIME
     canonical format (as required by the S/MIME specifications)
     if CMS_BINARY is set no translation occurs. This option
     should be used if the supplied data is in binary format
     otherwise the translation will corrupt it.

     The SignedData structure includes several CMS
     signedAttributes including the signing time, the CMS content
     type and the supported list of ciphers in an
     SMIMECapabilities attribute. If CMS_NOATTR is set then no
     signedAttributes will be used. If CMS_NOSMIMECAP is set then

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CMS_sign(3)                  OpenSSL                  CMS_sign(3)

     just the SMIMECapabilities are omitted.

     If present the SMIMECapabilities attribute indicates support
     for the following algorithms in preference order: 256 bit
     AES, Gost R3411-94, Gost 28147-89, 192 bit AES, 128 bit AES,
     triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2.  If
     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 not loaded.

     OpenSSL will by default identify signing certificates using
     issuer name and serial number. If CMS_USE_KEYID is set it
     will use the subject key identifier value instead. An error
     occurs if the signing certificate does not have a subject
     key identifier extension.

     If the flags CMS_STREAM is set then the returned
     CMS_ContentInfo structure is just initialized ready to
     perform the signing operation. The signing is however not
     performed and the data to be signed is not read from the
     data parameter. Signing is deferred until after the data has
     been written. In this way data can be signed in a single

     If the CMS_PARTIAL flag is set a partial CMS_ContentInfo
     structure is output to which additional signers and
     capabilities can be added before finalization.

     If the flag CMS_STREAM is set the returned CMS_ContentInfo
     structure is not complete and outputting its contents via a
     function that does not properly finalize the CMS_ContentInfo
     structure will give unpredictable results.

     Several functions including SMIME_write_CMS(),
     i2d_CMS_bio_stream(), PEM_write_bio_CMS_stream() finalize
     the structure. Alternatively finalization can be performed
     by obtaining the streaming ASN1 BIO directly using

     If a signer is specified it will use the default digest for
     the signing algorithm. This is SHA1 for both RSA and DSA

     If signcert and pkey are NULL then a certificates only CMS
     structure is output.

     The function CMS_sign() is a basic CMS signing function
     whose output will be suitable for many purposes. For finer
     control of the output format the certs, signcert and pkey
     parameters can all be NULL and the CMS_PARTIAL flag set.
     Then one or more signers can be added using the function
     CMS_sign_add1_signer(), non default digests can be used and

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CMS_sign(3)                  OpenSSL                  CMS_sign(3)

     custom attributes added. CCMMSS_ffiinnaall(()) must then be called to
     finalize the structure if streaming is not enabled.


     Some attributes such as counter signatures are not


     CMS_sign() returns either a valid CMS_ContentInfo structure
     or NULL if an error occurred. The error can be obtained from


     ERR_get_error(3), CMS_verify(3)


     CMS_sign() was added to OpenSSL 0.9.8

     The CMS_STREAM flag is only supported for detached data in
     OpenSSL 0.9.8, it is supported for embedded data in OpenSSL
     1.0.0 and later.

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