.\" $OpenBSD: CMS_add1_signer.3,v 1.10 2024/04/18 16:50:22 tb Exp $ .\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100 .\" .\" This file is a derived work. .\" The changes are covered by the following Copyright and license: .\" .\" Copyright (c) 2019 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: April 18 2024 $ .Dt CMS_ADD1_SIGNER 3 .Os .Sh NAME .Nm CMS_add1_signer , .Nm CMS_SignerInfo_sign .Nd add a signer to a CMS SignedData 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 .Fa signerInfos field of the .Vt SignedData structure .Fa cms , which should have been obtained from an initial call to .Xr CMS_sign 3 with the flag .Dv CMS_PARTIAL set, or which can be a valid .Vt SignedData structure in the case of re-signing. .Pp If .Fa md is .Dv NULL , the default digest for the public key algorithm of .Fa pkey is used. .Pp Unless the .Dv CMS_REUSE_DIGEST flag is set, the .Fa cms structure remains incomplete and must be finalized either by streaming (if applicable) or by a call to .Xr CMS_final 3 . .Pp The main purpose of .Fn CMS_add1_signer is to provide finer control over a CMS .Vt SignedData 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: .Bl -tag -width Ds .It Dv CMS_REUSE_DIGEST Attempt to copy the content digest value from one of the existing .Vt CMS_SignerInfo structures in .Fa cms while adding another signer. An error occurs if a matching digest value cannot be found to copy. The .Fa cms structure will be valid and finalized when this flag is set. .It Dv CMS_PARTIAL If this flag is set in addition to .Dv CMS_REUSE_DIGEST , the returned .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. .It Dv CMS_NOCERTS Do not add the signer's certificate to the .Fa certificates field of .Fa cms . The signer's certificate must still be supplied in the .Fa signcert parameter though. This flag can reduce the size of the signature if the signer's certificate can be obtained by other means, for example from a previously signed message. .It Dv CMS_NOATTR Leave the .Fa signedAttrs field of the returned .Vt CMS_SignedData structure empty. By default, several CMS .Vt SignedAttributes are added, including the signing time, the CMS content type, and the supported list of ciphers in an .Vt SMIMECapabilities attribute. .It Dv CMS_NOSMIMECAP Omit just the .Vt SMIMECapabilities attribute. .It Dv CMS_USE_KEYID Use the subject key identifier value to identify signing certificates. An error occurs if the signing certificate does not have a subject key identifier extension. By default, issuer name and serial number are used instead. .El .Pp If present, the .Vt SMIMECapabilities attribute indicates support for the following algorithms in preference order: 256-bit AES, 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. .Pp The .Fn CMS_SignerInfo_sign function explicitly signs .Fa si . Its main use is when the .Dv CMS_REUSE_DIGEST and .Dv CMS_PARTIAL flags were both set in the call to .Fn CMS_add1_signer that created .Fa si . .Sh RETURN VALUES .Fn CMS_add1_signer returns an internal pointer to the new .Vt CMS_SignerInfo structure just added or .Dv NULL if an error occurs. .Sh SEE ALSO .Xr CMS_ContentInfo_new 3 , .Xr CMS_final 3 , .Xr CMS_sign 3 , .Xr ERR_get_error 3 .Sh STANDARDS RFC 5652: Cryptographic Message Syntax, section 5.1: SignedData Type .Pp RFC 8419: Use of Edwards-Curve Digital Signature Algorithm (EdDSA) Signatures in the Cryptographic Message Syntax (CMS) .Pp RFC 8551: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version\ 4.0 Message Specification .Bl -dash -compact -offset indent .It section 2.5: Attributes and the SignerInfo Type .It section 2.5.2: SMIMECapabilities Attribute .El .Sh HISTORY .Fn CMS_add1_signer and .Fn CMS_SignerInfo_sign first appeared in OpenSSL 0.9.8h and have been available since .Ox 6.7 .