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       PKCS7_sign - create a PKCS#7 signedData structure


        #include <openssl/pkcs7.h>

        PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
                          BIO *data, int flags);


       PKCS7_sign() creates and returns a PKCS#7 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 PKCS#7 structure (for example any
       intermediate CAs in the chain).

       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
       PKCS7_TEXT flag is set MIME headers for type text/plain are prepended to the data.

       If PKCS7_NOCERTS is set the signer's certificate will not be included in the PKCS7
       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 PKCS7 structure, unless PKCS7_DETACHED is set in
       which case it is omitted. This is used for PKCS7 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 PKCS7_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 PKCS#7 authenticatedAttributes including the
       signing time, the PKCS#7 content type and the supported list of ciphers in an
       SMIMECapabilities attribute. If PKCS7_NOATTR is set then no authenticatedAttributes will
       be used. If PKCS7_NOSMIMECAP is set then just the SMIMECapabilities are omitted.

       If present the SMIMECapabilities attribute indicates support for the following algorithms:
       triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of these algorithms is
       disabled then it will not be included.

       If the flags PKCS7_STREAM is set then the returned PKCS7 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 pass.

       If the PKCS7_PARTIAL flag is set a partial PKCS7 structure is output to which additional
       signers and capabilities can be added before finalization.


       If the flag PKCS7_STREAM is set the returned PKCS7 structure is not complete and
       outputting its contents via a function that does not properly finalize the PKCS7 structure
       will give unpredictable results.

       Several functions including SMIME_write_PKCS7(), i2d_PKCS7_bio_stream(),
       PEM_write_bio_PKCS7_stream() finalize the structure. Alternatively finalization can be
       performed by obtaining the streaming ASN1 BIO directly using BIO_new_PKCS7().

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

       The certs, signcert and pkey parameters can all be NULL if the PKCS7_PARTIAL flag is set.
       One or more signers can be added using the function PKCS7_sign_add_signer(). PKCS7_final()
       must also be called to finalize the structure if streaming is not enabled. Alternative
       signing digests can also be specified using this method.

       If signcert and pkey are NULL then a certificates only PKCS#7 structure is output.

       In versions of OpenSSL before 1.0.0 the signcert and pkey parameters must NOT be NULL.


       Some advanced attributes such as counter signatures are not supported.


       PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred.  The
       error can be obtained from ERR_get_error(3).


       ERR_get_error(3), PKCS7_verify(3)


       The PKCS7_PARTIAL flag, and the ability for certs, signcert, and pkey parameters to be
       NULL were added in OpenSSL 1.0.0.

       The PKCS7_STREAM flag was added in OpenSSL 1.0.0.


       Copyright 2002-2016 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 <>.