.Dd $Mdocdate: November 11 2015 $
.Dt CMS_SIGN_ADD1_SIGNER 3
.Os
.Sh NAME
.Nm CMS_add1_signer ,
.Nm CMS_SignerInfo_sign
.Nd add a signer to a CMS_ContentInfo signed data structure
.Sh SYNOPSIS
.In openssl/cms.h
.Ft CMS_SignerInfo *
.Fo CMS_add1_signer
.Fa "CMS_ContentInfo *cms"
.Fa "X509 *signcert"
.Fa "EVP_PKEY *pkey"
.Fa "const EVP_MD *md"
.Fa "unsigned int flags"
.Fc
.Ft int
.Fo CMS_SignerInfo_sign
.Fa "CMS_SignerInfo *si"
.Fc
.Sh DESCRIPTION
.Fn CMS_add1_signer
adds a signer with certificate
.Fa signcert
and private key
.Fa pkey
using message digest
.Fa md
to the
.Vt CMS_ContentInfo
SignedData structure
.Fa cms .
.Pp
The
.Vt CMS_ContentInfo
structure should be obtained from an initial call to
.Xr CMS_sign 3
with the flag
.Dv CMS_PARTIAL
set or in the case or re-signing a valid
.Vt CMS_ContentInfo
SignedData structure.
.Pp
If the
.Fa md
parameter is
.Dv NULL ,
then the default digest for the public key algorithm will be used.
.Pp
Unless the
.Dv CMS_REUSE_DIGEST
flag is set, the returned
.Vt CMS_ContentInfo
structure is not complete and must be finalized either by streaming
(if applicable) or a call to
.Xr CMS_final 3 .
.Pp
The
.Fn CMS_SignerInfo_sign
function will explicitly sign a
.Vt CMS_SignerInfo
structure, its main use is when
.Dv CMS_REUSE_DIGEST
and
.Dv CMS_PARTIAL
flags are both set.
.Sh NOTES
The main purpose of
.Fn CMS_add1_signer
is to provide finer control over a CMS signed data structure where the
simpler
.Xr CMS_sign 3
function defaults are not appropriate.
For example if multiple signers or non default digest algorithms are
needed.
New attributes can also be added using the returned
.Vt CMS_SignerInfo
structure and the CMS attribute utility functions or the CMS signed
receipt request functions.
.Pp
Any of the following flags (OR'ed together) can be passed in the
.Fa flags
parameter.
.Pp
If
.Dv CMS_REUSE_DIGEST
is set, then an attempt is made to copy the content digest value from the
.Dv CMS_ContentInfo
structure: to add a signer to an existing structure.
An error occurs if a matching digest value cannot be found to copy.
The returned
.Dv CMS_ContentInfo
structure will be valid and finalized when this flag is set.
.Pp
If
.Dv CMS_PARTIAL
is set in addition to
.Dv CMS_REUSE_DIGEST
then the
.Vt CMS_SignerInfo
structure will not be finalized so additional attributes can be added.
In this case an explicit call to
.Fn CMS_SignerInfo_sign
is needed to finalize it.
.Pp
If
.Dv CMS_NOCERTS
is set, the signer's certificate will not be included in the
.Vt CMS_ContentInfo
structure, the signer's certificate must still be supplied in the
.Fa 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.
.Pp
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
.Dv CMS_NOATTR
is set, then no signedAttributes will be used.
If
.Dv CMS_NOSMIMECAP
is set, then just the SMIMECapabilities are omitted.
.Pp
OpenSSL will by default identify signing certificates using issuer name
and serial number.
If
.Dv 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.
.Pp
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.
.Pp
.Fn CMS_add1_signer
returns an internal pointer to the
.Dv CMS_SignerInfo
structure just added.
This can be used to set additional attributes before it is finalized.
.Sh RETURN VALUES
.Fn CMS_add1_signer
returns an internal pointer to the
.Vt CMS_SignerInfo
structure just added or
.Dv NULL
if an error occurs.
.Sh SEE ALSO
.Xr CMS_final 3 ,
.Xr CMS_sign 3 ,
.Xr ERR_get_error 3
.Sh HISTORY
.Fn CMS_add1_signer
was added to OpenSSL 0.9.8.