.\" $OpenBSD: CMS_sign.3,v 1.11 2024/04/18 16:50:22 tb Exp $ .\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2008 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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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_SIGN 3 .Os .Sh NAME .Nm CMS_sign .Nd create a CMS SignedData structure .Sh SYNOPSIS .In openssl/cms.h .Ft CMS_ContentInfo * .Fo CMS_sign .Fa "X509 *signcert" .Fa "EVP_PKEY *pkey" .Fa "STACK_OF(X509) *certs" .Fa "BIO *data" .Fa "unsigned int flags" .Fc .Sh DESCRIPTION .Fn CMS_sign creates and returns a CMS .Vt SignedData structure. .Fa signcert is the certificate to sign with, .Fa pkey is the corresponding private key. .Fa 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 .Dv NULL . .Pp The data to be signed is read from .Fa data . .Pp Any of the following flags (OR'ed together) can be passed in the .Fa flags argument: .Bl -tag -width Ds .It Dv CMS_TEXT Prepend MIME headers for the type text/plain to the data. Many S/MIME clients expect the signed content to include valid MIME headers. .It Dv CMS_NOCERTS Do not include the signer's certificate 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 signer's certificate can be obtained by other means, for example from a previously signed message. .It Dv CMS_DETACHED Omit the data being signed from the .Vt CMS_ContentInfo structure. This is used for .Vt CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed messages for example. .It Dv CMS_BINARY Do not translate the supplied content into MIME canonical format even though that is required by the S/MIME specifications. This option should be used if the supplied data is in binary format. Otherwise the translation will corrupt it. .It Dv CMS_NOATTR Do not add any .Vt SignedAttributes . By default, the .Fa signerInfos field includes several CMS .Vt SignedAttributes 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 . If present, the 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. .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. .It Dv CMS_STREAM Only initialize the returned .Vt CMS_ContentInfo structure to prepare it for performing the signing operation. The signing is however .Em not performed and the data to be signed is not read from the .Fa data parameter. Signing is deferred until after the data has been written. In this way, data can be signed in a single pass. The returned .Vt CMS_ContentInfo structure is .Em not complete and outputting its contents via a function that does not properly finalize the .Vt CMS_ContentInfo structure will give unpredictable results. Several functions including .Xr SMIME_write_CMS 3 , .Xr i2d_CMS_bio_stream 3 , or .Xr PEM_write_bio_CMS_stream 3 finalize the structure. Alternatively, finalization can be performed by obtaining the streaming ASN1 .Vt BIO directly using .Xr BIO_new_CMS 3 . .It Dv CMS_PARTIAL Output a partial .Vt CMS_ContentInfo structure to which additional signers and capabilities can be added before finalization. .El .Pp If a signer is specified, it will use the default digest for the signing algorithm. This is SHA1 for both RSA and DSA keys. .Pp If .Fa signcert and .Fa pkey are .Dv NULL , then a certificates only CMS structure is output. .Pp The function .Fn CMS_sign is a basic CMS signing function whose output will be suitable for many purposes. For finer control of the output format the .Fa certs , .Fa signcert and .Fa pkey parameters can all be .Dv NULL and the .Dv CMS_PARTIAL flag set. Then one or more signers can be added using the function .Xr CMS_add1_signer 3 , non default digests can be used and custom attributes added. .Xr CMS_final 3 must then be called to finalize the structure if streaming is not enabled. .Sh RETURN VALUES .Fn CMS_sign returns either a valid .Vt CMS_ContentInfo structure or .Dv NULL if an error occurred. The error can be obtained from .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr CMS_add0_cert 3 , .Xr CMS_add1_signer 3 , .Xr CMS_ContentInfo_new 3 , .Xr CMS_final 3 , .Xr CMS_sign_receipt 3 , .Xr CMS_verify 3 .Sh STANDARDS RFC 5652: Cryptographic Message Syntax (CMS) .Bl -dash -compact -offset indent .It section 5.1: SignedData Type .It section 5.3: SignerInfo Type .El .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, section 2.5.2: SMIMECapabilities Attribute .Sh HISTORY .Fn CMS_sign first appeared in OpenSSL 0.9.8h and has been available since .Ox 6.7 . .Sh BUGS Some attributes such as counter signatures are not supported.