How to: Sign and Envelop a Message
This example creates a CMS/PKCS #7 enveloped signed message by using System.Security.Cryptography.Pkcs. The message is first signed by a single signer and then encrypted for a single recipient. The message is then decrypted by using the recipient's private key, and the signature is verified. The example uses the SignedCms object, which allows a message to be signed and countersigned by one or more signers. It also uses the EnvelopedCms object, which allows messages to be encrypted for one or more recipients, or enveloped.
Example
This example uses the following classes:
EnvelopedCms
SignedCms
To run on a single computer, this example requires the following:
One public key certificate with the subject name "MessageSigner1" be in the My certificate store.
Another certificate with the subject name "Recipient1" be contained in both the AddressBook and My certificate stores.
Associated private keys be stored on the single computer.
The example code first acts as the message sender and then as the message recipient. The example uses the same public key credentials in each role. As such, the example requires that the public key certificate for the subject name "Recipient1" be in two stores. As the sender, it searches the AddressBook certificate store for the recipient's certificate, and uses that to encrypt the message. As the recipient, it searches the My certificate store for the certificate and uses the associated private key to decrypt the message.
.gif) Note |
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This example is only for illustrative purposes. Production environments might use a different model in which the sender and the recipient of the message execute in different processes with their unique public key credentials. |
Set up this example by using the Makecert.exe utility, one of several ways to do so. Certificate Creation Tool (Makecert.exe) is a convenient utility for testing certificates. In a production environment, certificates are generated by a certification authority.
The following Makecert commands generate the required public key certificates and private keys.
Makecert -n "CN=MessageSigner1" -ss My
Makecert -n "CN=Recipient1" -sky exchange -ss M
These commands place the appropriate public key certificates in the My certificate store. To get the public key certificate for subject name "Recipient1" in the AddressBook certificate store, export the public key certificate, and then import it into the AddressBook store by following the procedure in How to: Export and Import a Public Key Certificate.
// Copyright (c) Microsoft Corporation. All rights reserved.
#region Using directives
using System;
using System.Security.Cryptography;
using System.Security.Cryptography.Pkcs;
using System.Security.Cryptography.X509Certificates;
using System.Text;
#endregion
namespace SigningAndEnvelopingMessage
{
class EnvelopedSignedCms
{
const String signerName = "MessageSigner1";
const String recipientName = "Recipient1";
static void Main(string[] args)
{
byte[] origMsg;
Console.WriteLine("System.Security.Cryptography.Pkcs " +
"Sample: Encrypted, signed, decrypted, and " +
"verified message");
// Original message.
const String msg = "Here are the sales figures for the " +
"upcoming quarterly report to Wall Street.";
Console.WriteLine("\nOriginal message (len {0}): {1} ",
msg.Length, msg);
// Convert message to array of bytes for signing.
Encoding unicode = Encoding.Unicode;
byte[] msgBytes = unicode.GetBytes(msg);
Console.WriteLine("\n\n------------------------------");
Console.WriteLine(" SETUP OF CREDENTIALS ");
Console.WriteLine("------------------------------\n");
// The signer's private key, obtained by association with
// their signing certificate, is necessary to sign the
// message.
X509Certificate2 signerCert = GetSignerCert();
// The recipient's certificate is necessary to encrypt
// the message for that recipient.
X509Certificate2 recipientCert = GetRecipientCert();
Console.WriteLine("\n\n----------------------");
Console.WriteLine(" SENDER SIDE ");
Console.WriteLine("----------------------\n");
byte[] encodedSignedCms = SignMsg(msgBytes, signerCert);
// Encrypt the encoded SignedCms message.
byte[] encodedEnvelopedCms = EncryptMsg(encodedSignedCms,
recipientCert);
Console.Write("\nMessage after encryption (len {0}): ",
encodedEnvelopedCms.Length);
foreach (byte b in encodedEnvelopedCms)
{
Console.Write("{0:x}", b);
}
Console.WriteLine();
Console.WriteLine("\n\n------------------------");
Console.WriteLine(" RECIPIENT SIDE ");
Console.WriteLine("------------------------\n");
encodedSignedCms = DecryptMsg(encodedEnvelopedCms);
// Get the original message back after verification so
// it can be displayed.
if (VerifyMsg(encodedSignedCms, out origMsg))
{
Console.WriteLine("\nMessage verified");
}
else
{
Console.WriteLine("\nMessage failed to verify");
}
// Convert Unicode bytes to the original message string.
Console.WriteLine("\nDecrypted Authenticated Message: {0}",
unicode.GetString(origMsg));
}
// Open the My (or Personal) certificate store. Search for
// credentials with which to sign the message. The certificate
// must have a the subject name "MessageSigner1".
static public X509Certificate2 GetSignerCert()
{
// Open the My certificate store.
X509Store storeMy = new X509Store(StoreName.My,
StoreLocation.CurrentUser);
storeMy.Open(OpenFlags.ReadOnly);
// Display certificates to help troubleshoot the
// example's setup.
Console.WriteLine("Found certs with the following subject " +
"names in the {0} store:", storeMy.Name);
foreach (X509Certificate2 cert in storeMy.Certificates)
{
Console.WriteLine("\t{0}", cert.SubjectName.Name);
}
// Find the signer's certificate.
X509Certificate2Collection certColl =
storeMy.Certificates.Find(X509FindType.FindBySubjectName,
signerName, false);
Console.WriteLine(
"Found {0} certificates in the {1} store with name {2}",
certColl.Count, storeMy.Name, signerName);
// Check to see if the certificate suggested by the example
// requirements is not present.
if (certColl.Count == 0)
{
Console.WriteLine(
"A suggested certificate to use for this example " +
"is not in the certificate store. Select " +
"an alternate certificate to use for " +
"signing the message.");
}
storeMy.Close();
return certColl[0];
}
// Open the AddressBook (called Other in Internet Explorer)
// certificate store and search for a recipient
// certificate with which to encrypt the message. The certificate
// must have the subject name "Recipient1".
static public X509Certificate2 GetRecipientCert()
{
// Open the AddressBook local user X509 certificate store.
X509Store storeAddressBook = new X509Store(StoreName.
AddressBook, StoreLocation.CurrentUser);
storeAddressBook.Open(OpenFlags.ReadOnly);
// Display certificates to help troubleshoot the
// example's setup.
Console.WriteLine(
"Found certs with the following subject names in the " +
"{0} store:",
storeAddressBook.Name);
foreach (X509Certificate2 cert in storeAddressBook.Certificates)
{
Console.WriteLine("\t{0}", cert.SubjectName.Name);
}
// Get recipient certificate.
// For purposes of this sample, do not validate the
// certificate. Note that in a production environment,
// validating the certificate will probably be necessary.
X509Certificate2Collection certColl = storeAddressBook.
Certificates.Find(X509FindType.FindBySubjectName,
recipientName, false);
Console.WriteLine(
"Found {0} certificates in the {1} store with name {2}",
certColl.Count, storeAddressBook.Name, recipientName);
// Check to see if the certificate suggested by the example
// requirements is not present.
if (certColl.Count == 0)
{
Console.WriteLine(
"A suggested certificate to use for this example " +
"is not in the certificate store. Select " +
"an alternate certificate to use for " +
"signing the message.");
}
storeAddressBook.Close();
return certColl[0];
}
// Sign the message by the using the private key of the signer.
// Note that signer's public key certificate is input here
// because it is used to locate the corresponding private key.
static public byte[] SignMsg(
Byte[] msg,
X509Certificate2 signerCert)
{
// Place message in a ContentInfo object.
// This is required to build a SignedCms object.
ContentInfo contentInfo = new ContentInfo(msg);
// Instantiate SignedCms object with the ContentInfo above.
// Has default SubjectIdentifierType IssuerAndSerialNumber.
// Has default Detached property value false, so message is
// included in the encoded SignedCms.
SignedCms signedCms = new SignedCms(contentInfo);
// Formulate a CmsSigner object, which has all the needed
// characteristics of the signer.
CmsSigner cmsSigner = new CmsSigner(signerCert);
// Sign the PKCS #7 message.
Console.Write("Computing signature with signer subject " +
"name {0} ... ", signerCert.SubjectName.Name);
signedCms.ComputeSignature(cmsSigner);
Console.WriteLine("Done.");
// Encode the PKCS #7 message.
return signedCms.Encode();
}
// Verify the encoded SignedCms message and return a Boolean
// value that specifies whether the verification was successful.
// Also return the original message that was signed, which is
// available as part of the SignedCms message after it
// is decoded.
static public bool VerifyMsg(byte[] encodedSignedCms,
out byte[] origMsg)
{
// Prepare a SignedCms object in which to decode
// and verify.
SignedCms signedCms = new SignedCms();
signedCms.Decode(encodedSignedCms);
// Catch a verification exception in the event you want to
// advise the message recipient that security actions
// might be appropriate.
try
{
// Verify signature. Do not validate signer
// certificate for the purposes of this example.
// Note that in a production environment, validating
// the signer certificate chain will probably be
// necessary.
Console.Write("Checking signature on message ... ");
signedCms.CheckSignature(true);
Console.WriteLine("Done.");
}
catch (System.Security.Cryptography.CryptographicException e)
{
Console.WriteLine("VerifyMsg caught exception: {0}",
e.Message);
Console.WriteLine("The message may have been modified " +
"in transit or storage. Authenticity of the " +
"message is not guaranteed.");
origMsg = null;
return false;
}
origMsg = signedCms.ContentInfo.Content;
return true;
}
// Encrypt the message with the public key of
// the recipient. This is done by enveloping the message by
// using a EnvelopedCms object.
static public byte[] EncryptMsg(Byte[] msg,
X509Certificate2 recipientCert)
{
// Place message in a ContentInfo object.
// This is required to build an EnvelopedCms object.
ContentInfo contentInfo = new ContentInfo(msg);
// Instantiate EnvelopedCms object with the ContentInfo
// above.
// Has default SubjectIdentifierType IssuerAndSerialNumber.
// Has default ContentEncryptionAlgorithm property value
// RSA_DES_EDE3_CBC.
EnvelopedCms envelopedCms = new EnvelopedCms(contentInfo);
// Formulate a CmsRecipient object that
// represents information about the recipient
// to encrypt the message for.
CmsRecipient recip1 = new CmsRecipient(
SubjectIdentifierType.IssuerAndSerialNumber,
recipientCert);
Console.Write("Encrypting data for a single recipient of " +
"subject name {0} ... ",
recip1.Certificate.SubjectName.Name);
// Encrypt the message for the recipient.
envelopedCms.Encrypt(recip1);
Console.WriteLine("Done.");
// The encoded EnvelopedCms message contains the encrypted
// message and the information about each recipient that
// the message was enveloped for.
return envelopedCms.Encode();
}
// Decrypt the encoded EnvelopedCms message.
static public Byte[] DecryptMsg(byte[] encodedEnvelopedCms)
{
// Prepare object in which to decode and decrypt.
EnvelopedCms envelopedCms = new EnvelopedCms();
// Decode the message.
envelopedCms.Decode(encodedEnvelopedCms);
// Display the number of recipients the message is
// enveloped for; it should be 1 for this example.
DisplayEnvelopedCms(envelopedCms, false);
// Decrypt the message for the single recipient.
// Note that the following call to the Decrypt method
// accomplishes the same result:
// envelopedCms.Decrypt();
Console.Write("Decrypting Data ... ");
envelopedCms.Decrypt(envelopedCms.RecipientInfos[0]);
Console.WriteLine("Done.");
return envelopedCms.Encode();
}
// Display the ContentInfo property of a SignedCms object.
private void DisplaySignedCmsContent(String desc,
SignedCms signedCms)
{
Console.WriteLine(desc + " (length {0}): ",
signedCms.ContentInfo.Content.Length);
foreach (byte b in signedCms.ContentInfo.Content)
{
Console.Write(b.ToString() + " ");
}
Console.WriteLine();
}
// Display the ContentInfo property of an EnvelopedCms object.
static private void DisplayEnvelopedCmsContent(String desc,
EnvelopedCms envelopedCms)
{
Console.WriteLine(desc + " (length {0}): ",
envelopedCms.ContentInfo.Content.Length);
foreach (byte b in envelopedCms.ContentInfo.Content)
{
Console.Write(b.ToString() + " ");
}
Console.WriteLine();
}
// Display some properties of an EnvelopedCms object.
static private void DisplayEnvelopedCms(EnvelopedCms e,
Boolean displayContent)
{
Console.WriteLine("\nEnveloped PKCS #7 Message Information:");
Console.WriteLine(
"\tThe number of recipients for the Enveloped PKCS #7 " +
"is: {0}",
e.RecipientInfos.Count);
for (int i = 0; i < e.RecipientInfos.Count; i++)
{
Console.WriteLine(
"\tRecipient #{0} has type {1}.",
i + 1,
e.RecipientInfos[i].RecipientIdentifier.Type);
}
if (displayContent)
{
DisplayEnvelopedCmsContent("Enveloped PKCS #7 Content", e);
}
Console.WriteLine();
}
}
}
See Also
Tasks
How to: Sign Messages by One Signer
How to: Sign a Message by Multiple Signers
How to: Countersign a Message
How to: Envelope a Message for One Recipient
How to: Envelope a Message for Multiple Recipients