122 lines
4.6 KiB
Plaintext
122 lines
4.6 KiB
Plaintext
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=pod
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=head1 NAME
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PKCS7_sign - create a PKCS#7 signedData structure
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=head1 SYNOPSIS
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#include <openssl/pkcs7.h>
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PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
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BIO *data, int flags);
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=head1 DESCRIPTION
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PKCS7_sign() creates and returns a PKCS#7 signedData structure.
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I<signcert> is the certificate to sign with, I<pkey> is the corresponding
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private key. I<certs> is an optional set of extra certificates to include
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in the PKCS#7 structure (for example any intermediate CAs in the chain).
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The data to be signed is read from BIO I<data>.
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I<flags> is an optional set of flags.
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Any of the following flags (ored together) can be passed in the I<flags>
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Many S/MIME clients expect the signed content to include valid MIME headers. If
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the B<PKCS7_TEXT> flag is set MIME headers for type C<text/plain> are prepended
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to the data.
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If B<PKCS7_NOCERTS> is set the signer's certificate and the extra I<certs>
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will not be included in the PKCS7 structure.
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The signer's certificate must still be supplied in the I<signcert> parameter
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though. This can reduce the size of the signatures if the signer's certificates
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can be obtained by other means: for example a previously signed message.
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The data being signed is included in the PKCS7 structure, unless
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B<PKCS7_DETACHED> is set in which case it is omitted. This is used for PKCS7
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detached signatures which are used in S/MIME plaintext signed messages for
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example.
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Normally the supplied content is translated into MIME canonical format (as
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required by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation
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occurs. This option should be used if the supplied data is in binary format
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otherwise the translation will corrupt it.
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The signedData structure includes several PKCS#7 authenticatedAttributes
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including the signing time, the PKCS#7 content type and the supported list of
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ciphers in an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no
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authenticatedAttributes will be used. If B<PKCS7_NOSMIMECAP> is set then just
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the SMIMECapabilities are omitted.
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If present the SMIMECapabilities attribute indicates support for the following
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algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
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these algorithms is disabled then it will not be included.
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If the flags B<PKCS7_STREAM> is set then the returned B<PKCS7> structure is
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just initialized ready to perform the signing operation. The signing is however
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B<not> performed and the data to be signed is not read from the I<data>
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parameter. Signing is deferred until after the data has been written. In this
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way data can be signed in a single pass.
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If the B<PKCS7_PARTIAL> flag is set a partial B<PKCS7> structure is output to
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which additional signers and capabilities can be added before finalization.
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=head1 NOTES
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If the flag B<PKCS7_STREAM> is set the returned B<PKCS7> structure is B<not>
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complete and outputting its contents via a function that does not properly
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finalize the B<PKCS7> structure will give unpredictable results.
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Several functions including SMIME_write_PKCS7(), i2d_PKCS7_bio_stream(),
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PEM_write_bio_PKCS7_stream() finalize the structure. Alternatively finalization
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can be performed by obtaining the streaming ASN1 B<BIO> directly using
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BIO_new_PKCS7().
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If a signer is specified it will use the default digest for the signing
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algorithm. This is B<SHA1> for both RSA and DSA keys.
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The I<certs>, I<signcert> and I<pkey> parameters can all be
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NULL if the B<PKCS7_PARTIAL> flag is set. One or more signers can be added
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using the function PKCS7_sign_add_signer(). PKCS7_final() must also be
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called to finalize the structure if streaming is not enabled. Alternative
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signing digests can also be specified using this method.
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If I<signcert> and I<pkey> are NULL then a certificates only
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PKCS#7 structure is output.
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In versions of OpenSSL before 1.0.0 the I<signcert> and I<pkey> parameters must
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not be NULL.
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=head1 BUGS
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Some advanced attributes such as counter signatures are not supported.
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=head1 RETURN VALUES
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PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error
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occurred. The error can be obtained from ERR_get_error(3).
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=head1 SEE ALSO
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L<ERR_get_error(3)>, L<PKCS7_verify(3)>
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=head1 HISTORY
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The B<PKCS7_PARTIAL> flag, and the ability for I<certs>, I<signcert>,
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and I<pkey> parameters to be NULL were added in OpenSSL 1.0.0.
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The B<PKCS7_STREAM> flag was added in OpenSSL 1.0.0.
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=head1 COPYRIGHT
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Copyright 2002-2022 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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