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a528d4f0a9
If something was "present in all versions" of SSLeay, or if it was added to a version of SSLeay (and therefore predates OpenSSL), remove mention of it. Documentation history now starts with OpenSSL. Remove mention of all history before OpenSSL 0.9.8, inclusive. Remove all AUTHOR sections. Reviewed-by: Tim Hudson <tjh@openssl.org>
120 lines
4.8 KiB
Plaintext
120 lines
4.8 KiB
Plaintext
=pod
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=head1 NAME
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CMS_sign - create a CMS SignedData structure
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=head1 SYNOPSIS
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#include <openssl/cms.h>
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CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, unsigned int flags);
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=head1 DESCRIPTION
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CMS_sign() creates and returns a CMS SignedData structure. B<signcert> is
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the certificate to sign with, B<pkey> is the corresponding private key.
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B<certs> is an optional additional set of certificates to include in the CMS
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structure (for example any intermediate CAs in the chain). Any or all of
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these parameters can be B<NULL>, see B<NOTES> below.
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The data to be signed is read from BIO B<data>.
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B<flags> is an optional set of flags.
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=head1 NOTES
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Any of the following flags (ored together) can be passed in the B<flags>
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parameter.
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Many S/MIME clients expect the signed content to include valid MIME headers. If
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the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are prepended
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to the data.
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If B<CMS_NOCERTS> is set the signer's certificate will not be included in the
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CMS_ContentInfo structure, the signer's certificate must still be supplied in
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the B<signcert> parameter though. This can reduce the size of the signature if
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the signers certificate can be obtained by other means: for example a
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previously signed message.
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The data being signed is included in the CMS_ContentInfo structure, unless
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B<CMS_DETACHED> is set in which case it is omitted. This is used for
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CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed
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messages for 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<CMS_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 CMS signedAttributes including the
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signing time, the CMS content type and the supported list of ciphers in an
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SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes
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will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are
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omitted.
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If present the SMIMECapabilities attribute indicates support for the following
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algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192
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bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2.
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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
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not loaded.
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OpenSSL will by default identify signing certificates using issuer name
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and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
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identifier value instead. An error occurs if the signing certificate does not
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have a subject key identifier extension.
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If the flags B<CMS_STREAM> is set then the returned B<CMS_ContentInfo>
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structure is just initialized ready to perform the signing operation. The
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signing is however B<not> performed and the data to be signed is not read from
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the B<data> parameter. Signing is deferred until after the data has been
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written. In this way data can be signed in a single pass.
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If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
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output to which additional signers and capabilities can be added before
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finalization.
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If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
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B<not> complete and outputting its contents via a function that does not
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properly finalize the B<CMS_ContentInfo> structure will give unpredictable
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results.
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Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
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PEM_write_bio_CMS_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_CMS().
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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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If B<signcert> and B<pkey> are NULL then a certificates only CMS structure is
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output.
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The function CMS_sign() is a basic CMS signing function whose output will be
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suitable for many purposes. For finer control of the output format the
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B<certs>, B<signcert> and B<pkey> parameters can all be B<NULL> and the
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B<CMS_PARTIAL> flag set. Then one or more signers can be added using the
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function CMS_sign_add1_signer(), non default digests can be used and custom
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attributes added. B<CMS_final()> must then be called to finalize the
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structure if streaming is not enabled.
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=head1 BUGS
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Some attributes such as counter signatures are not supported.
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=head1 RETURN VALUES
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CMS_sign() returns either a valid CMS_ContentInfo 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<CMS_verify(3)>
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=head1 HISTORY
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The B<CMS_STREAM> flag is only supported for detached data in OpenSSL 0.9.8,
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it is supported for embedded data in OpenSSL 1.0.0 and later.
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=cut
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