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121 lines
4.9 KiB
121 lines
4.9 KiB
=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)|ERR_get_error(3)>, L<CMS_verify(3)|CMS_verify(3)> |
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=head1 HISTORY |
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CMS_sign() was added to OpenSSL 0.9.8 |
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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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