---
title: "Co-signatures"
description: "CAdES co-signatures in PKI SDK: how to group the parallel signatures of several signers of the same document in a single package, with CadesSigner."
canonical: "https://docs.lacunasoftware.com/en-us/articles/pki-sdk/signatures/cades/co-sign"
locale: "en"
product: "PKI SDK"
last_updated: "2026-10-12"
---

# Co-signatures

PKI SDK lets you group different signers of the same document in a single signature package. These parallel signatures are
called co-signatures, and the CAdES standard provides for them.

The example below shows a basic co-signature:

```cs
// Previous basic CAdES signature
byte[] cadesSig1 = ...

// Co-signing the cadesSig1 signature
PKCertificateWithKey signingCert2 = ...
var signer2 = new CadesSigner();
signer2.SetSigningCertificate(signingCert2);
signer2.SetDataToSign(toSign);
signer2.SetPolicy(policy);

// Setting the previous signature to co-sign
signer2.SetSignatureToCoSign(cadesSig1);

signer2.ComputeSignature();

byte[] cadesCoSig = signer2.GetSignature();
```

> **Note**
>
> If the cadesSig1 signature already has the signed document in its encapsulated content, you don't need to call
> @Lacuna.Pki.Cades.CadesSigner.SetDataToSign(System.Byte[]) on the co-signature.

If you have parallel signatures of the same document that were created without
@Lacuna.Pki.Cades.CadesSigner.SetSignatureToCoSign(System.Byte[]), you can still merge them into a co-signature with the
`Lacuna.Pki.Cades.CadesSignatureEditor.MergeSignatures(IEnumerable<Lacuna.Pki.Cades.CadesSignature>)` method of the
@Lacuna.Pki.Cades.CadesSignatureEditor class.

## See also

* @Lacuna.Pki.Cades.CadesSigner
* @Lacuna.Pki.Cades.CadesSignatureEditor