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Diffstat (limited to 'openssl/doc/crypto/CMS_sign.pod')
| -rw-r--r-- | openssl/doc/crypto/CMS_sign.pod | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/openssl/doc/crypto/CMS_sign.pod b/openssl/doc/crypto/CMS_sign.pod new file mode 100644 index 000000000..2cc72de32 --- /dev/null +++ b/openssl/doc/crypto/CMS_sign.pod @@ -0,0 +1,121 @@ +=pod + +=head1 NAME + + CMS_sign - create a CMS SignedData structure + +=head1 SYNOPSIS + + #include <openssl/cms.h> + + CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, unsigned int flags); + +=head1 DESCRIPTION + +CMS_sign() creates and returns a CMS SignedData structure. B<signcert> is +the certificate to sign with, B<pkey> is the corresponding private key. +B<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 B<NULL>, see B<NOTES> below. + +The data to be signed is read from BIO B<data>. + +B<flags> is an optional set of flags. + +=head1 NOTES + +Any of the following flags (ored together) can be passed in the B<flags> +parameter. + +Many S/MIME clients expect the signed content to include valid MIME headers. If +the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are prepended +to the data. + +If B<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 B<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 +B<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 B<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 B<CMS_NOATTR> is set then no signedAttributes +will be used. If B<CMS_NOSMIMECAP> is set then 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 B<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 B<CMS_STREAM> is set then the returned B<CMS_ContentInfo> +structure is just initialized ready to perform the signing operation. The +signing is however B<not> performed and the data to be signed is not read from +the B<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 B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is +output to which additional signers and capabilities can be added before +finalization. + +If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is +B<not> complete and outputting its contents via a function that does not +properly finalize the B<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 B<BIO> directly using +BIO_new_CMS(). + +If a signer is specified it will use the default digest for the signing +algorithm. This is B<SHA1> for both RSA and DSA keys. + +If B<signcert> and B<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 +B<certs>, B<signcert> and B<pkey> parameters can all be B<NULL> and the +B<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 custom +attributes added. B<CMS_final()> must then be called to finalize the +structure if streaming is not enabled. + +=head1 BUGS + +Some attributes such as counter signatures are not supported. + +=head1 RETURN VALUES + +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). + +=head1 SEE ALSO + +L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_verify(3)|CMS_verify(3)> + +=head1 HISTORY + +CMS_sign() was added to OpenSSL 0.9.8 + +The B<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. + +=cut |