Programma C di esempio: codifica di un messaggio in busta firmato
L'esempio seguente crea, firma e busta un messaggio e illustra le attività e le funzioni CryptoAPI seguenti:
- Acquisizione dell'handle di un CSP tramite CryptAcquireContext.
- Apertura di un archivio di sistema tramite CertOpenStore.
- Ricerca di certificati firmatari e destinatari tramite CertFindCertificateInStore.
- Inizializzazione di strutture di dati appropriate per la firma di un messaggio in busto.
- Individuazione della lunghezza del messaggio in busta tramite CryptMsgCalculateEncodedLength.
- Creazione e firma del messaggio usando CryptMsgOpenToEncode, CryptMsgUpdate e CryptMsgGetParam.
- Avvolgendo il messaggio firmato e codificato per un ricevitore usando CryptMsgOpenToEncode, CryptMsgUpdate e CryptMsgGetParam.
Questo esempio avrà esito negativo se non esiste una chiave privata utilizzabile nel contenitore di chiavi predefinito. Se la chiave privata necessaria non è disponibile, è possibile usare il codice che usa CryptAcquireCertificatePrivateKey, come illustrato nell'esempio di codice Esempio di programma C: Invio e ricezione di un messaggio firmato e crittografato.
In questo esempio viene usata la funzione MyHandleError. Il codice per questa funzione è incluso nell'esempio. Il codice per questa e altre funzioni ausiliarie è elencato anche in per utilizzo generico Funzioni.
#pragma comment(lib, "crypt32.lib")
#include <stdio.h>
#include <windows.h>
#include <Wincrypt.h>
#define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING)
void MyHandleError(char *s);
void main(void)
{
//-------------------------------------------------------------------
// Copyright (C) Microsoft. All rights reserved.
// Declare and initialize variables.
BYTE* pbContent = (BYTE*) "Security is our only business.";
// a byte pointer
DWORD cbContent = strlen((char *) pbContent)+1;
// the size of the message
HCERTSTORE hStoreHandle;
HCRYPTPROV hCryptProv;
PCCERT_CONTEXT pSignerCert; // signer's certificate
PCCERT_CONTEXT pRecipCert; // receiver's certificate
LPWSTR pswzRecipientName = L"Hortense";
LPWSTR pswzCertSubject = L"Full Test Cert";
PCERT_INFO RecipCertArray[1];
DWORD ContentEncryptAlgSize;
CRYPT_ALGORITHM_IDENTIFIER ContentEncryptAlgorithm;
CMSG_ENVELOPED_ENCODE_INFO EnvelopedEncodeInfo;
DWORD cbEncodedBlob;
BYTE *pbEncodedBlob;
DWORD cbSignedBlob;
BYTE *pbSignedBlob;
HCRYPTMSG hMsg;
DWORD HashAlgSize;
CRYPT_ALGORITHM_IDENTIFIER HashAlgorithm;
CMSG_SIGNER_ENCODE_INFO SignerEncodeInfo;
CERT_BLOB SignerCertBlob;
CERT_BLOB SignerCertBlobArray[1];
CMSG_SIGNER_ENCODE_INFO SignerEncodeInfoArray[1];
CMSG_SIGNED_ENCODE_INFO SignedMsgEncodeInfo;
//-------------------------------------------------------------------
// Begin processing. Display the original message.
printf("The original message => %s\n",pbContent);
//-------------------------------------------------------------------
// Acquire a cryptographic provider.
if(CryptAcquireContext(
&hCryptProv, // address for handle to be returned
NULL, // use the current user's logon name
NULL, // use the default provider
PROV_RSA_FULL, // provider type
0)) // zero allows access to private keys
{
printf("Context CSP acquired. \n");
}
else
{
if ( GetLastError() == NTE_BAD_KEYSET)
{
printf("A Usable private key was not found \n");
printf("in the default key container. Either a \n");
printf("private key must be generated in that container \n");
printf("or CryptAquireCertificatePrivateKey can be used \n");
printf("to gain access to the needed private key.");
}
MyHandleError("CryptAcquireContext failed.");
}
//-------------------------------------------------------------------
// Open the My system certificate store.
if(hStoreHandle = CertOpenStore(
CERT_STORE_PROV_SYSTEM,
0,
NULL,
CERT_SYSTEM_STORE_CURRENT_USER,
L"MY"))
{
printf("The MY system store is open. \n");
}
else
{
MyHandleError( "Error getting store handle.");
}
//-------------------------------------------------------------------
// Get the signer's certificate. This certificate must be in the
// My store, and its private key must be available.
if(pSignerCert = CertFindCertificateInStore(
hStoreHandle,
MY_ENCODING_TYPE,
0,
CERT_FIND_SUBJECT_STR,
pswzCertSubject,
NULL))
{
printf("Found certificate for %S.\n",pswzCertSubject);
}
else
{
MyHandleError("Signer certificate not found.");
}
//-------------------------------------------------------------------
// Initialize the algorithm identifier structure.
HashAlgSize = sizeof(HashAlgorithm);
memset(&HashAlgorithm, 0, HashAlgSize); // initialize to zero
HashAlgorithm.pszObjId = szOID_RSA_MD5; // initialize the
// necessary member
//-------------------------------------------------------------------
// Initialize the CMSG_SIGNER_ENCODE_INFO structure.
memset(&SignerEncodeInfo, 0, sizeof(CMSG_SIGNER_ENCODE_INFO));
SignerEncodeInfo.cbSize = sizeof(CMSG_SIGNER_ENCODE_INFO);
SignerEncodeInfo.pCertInfo = pSignerCert->pCertInfo;
SignerEncodeInfo.hCryptProv = hCryptProv;
SignerEncodeInfo.dwKeySpec = AT_KEYEXCHANGE;
SignerEncodeInfo.HashAlgorithm = HashAlgorithm;
SignerEncodeInfo.pvHashAuxInfo = NULL;
//-------------------------------------------------------------------
// Create an array of one.
// Note: The current program is set up for only a single signer.
SignerEncodeInfoArray[0] = SignerEncodeInfo;
//-------------------------------------------------------------------
// Initialize the CMSG_SIGNED_ENCODE_INFO structure.
SignerCertBlob.cbData = pSignerCert->cbCertEncoded;
SignerCertBlob.pbData = pSignerCert->pbCertEncoded;
//-------------------------------------------------------------------
// Initialize the array of one CertBlob.
SignerCertBlobArray[0] = SignerCertBlob;
memset(&SignedMsgEncodeInfo, 0, sizeof(CMSG_SIGNED_ENCODE_INFO));
SignedMsgEncodeInfo.cbSize = sizeof(CMSG_SIGNED_ENCODE_INFO);
SignedMsgEncodeInfo.cSigners = 1;
SignedMsgEncodeInfo.rgSigners = SignerEncodeInfoArray;
SignedMsgEncodeInfo.cCertEncoded = 1;
SignedMsgEncodeInfo.rgCertEncoded = SignerCertBlobArray;
SignedMsgEncodeInfo.rgCrlEncoded = NULL;
//-------------------------------------------------------------------
// Get the size of the encoded, signed message BLOB.
if(cbSignedBlob = CryptMsgCalculateEncodedLength(
MY_ENCODING_TYPE, // message encoding type
0, // flags
CMSG_SIGNED, // message type
&SignedMsgEncodeInfo, // pointer to structure
NULL, // inner content OID
cbContent)) // size of content
{
printf("%d, the length of data calculated. \n",cbSignedBlob);
}
else
{
if ( GetLastError() == NTE_BAD_KEYSET)
{
printf("A Usable private key was not found \n");
printf("in the default key container. Either a \n");
printf("private key must be generated in that container \n");
printf("or CryptAquireCertificatePRivateKey can be used \n");
printf("to gain access to the needed private key.");
}
MyHandleError("Getting cbSignedBlob length failed.");
}
//-------------------------------------------------------------------
// Allocate memory for the encoded BLOB.
if(pbSignedBlob = (BYTE *) malloc(cbSignedBlob))
{
printf("Memory has been allocated for the signed message. \n");
}
else
{
MyHandleError("Memory allocation failed.");
}
//-------------------------------------------------------------------
// Open a message to encode.
if(hMsg = CryptMsgOpenToEncode(
MY_ENCODING_TYPE, // encoding type
0, // flags
CMSG_SIGNED, // message type
&SignedMsgEncodeInfo, // pointer to structure
NULL, // inner content OID
NULL)) // stream information (not used)
{
printf("The message to be encoded has been opened. \n");
}
else
{
MyHandleError("OpenToEncode failed.");
}
//-------------------------------------------------------------------
// Update the message with the data.
if(CryptMsgUpdate(
hMsg, // handle to the message
pbContent, // pointer to the content
cbContent, // size of the content
TRUE)) // last call
{
printf("Content has been added to the encoded message. \n");
}
else
{
MyHandleError("MsgUpdate failed.");
}
//-------------------------------------------------------------------
// Get the resulting message.
if(CryptMsgGetParam(
hMsg, // handle to the message
CMSG_CONTENT_PARAM, // parameter type
0, // index
pbSignedBlob, // pointer to the BLOB
&cbSignedBlob)) // size of the BLOB
{
printf("Message encoded successfully. \n");
}
else
{
MyHandleError("MsgGetParam failed.");
}
//-------------------------------------------------------------------
// pbSignedBlob now points to the encoded, signed content.
//-------------------------------------------------------------------
// Get a pointer to the recipient certificate.
// For this program, the recipient's certificate must also be in the
// My store. At this point, only the recipient's public key is needed.
// To open the enveloped message, however, the recipient's
// private key must also be available.
if(pRecipCert=CertFindCertificateInStore(
hStoreHandle,
MY_ENCODING_TYPE, // use X509_ASN_ENCODING
0, // no dwFlags needed
CERT_FIND_SUBJECT_STR, // find a certificate with a
// subject that matches the
// string in the next parameter
pswzRecipientName, // the Unicode string to be found
// in a certificate's subject
NULL)) // NULL for the first call to the
// function
// in all subsequent
// calls, it is the last pointer
// returned by the function
{
printf("Certificate for %S found. \n", pswzRecipientName);
}
else
{
MyHandleError("Could not find the countersigner's "
"certificate.");
}
//-------------------------------------------------------------------
// Initialize the first element of the array of CERT_INFOs.
// In this example, there is only a single recipient.
RecipCertArray[0] = pRecipCert->pCertInfo;
//-------------------------------------------------------------------
// Initialize the symmetric-encryption algorithm identifier
// structure.
ContentEncryptAlgSize = sizeof(ContentEncryptAlgorithm);
memset(&ContentEncryptAlgorithm,
0,
ContentEncryptAlgSize); // initialize to zero
//-------------------------------------------------------------------
// Initialize the necessary members. This particular OID does not
// need any parameters. Some OIDs, however, will require that
// the other members be initialized.
ContentEncryptAlgorithm.pszObjId = szOID_RSA_RC4;
//-------------------------------------------------------------------
// Initialize the CMSG_ENVELOPED_ENCODE_INFO structure.
memset(&EnvelopedEncodeInfo,
0,
sizeof(CMSG_ENVELOPED_ENCODE_INFO));
EnvelopedEncodeInfo.cbSize = sizeof(CMSG_ENVELOPED_ENCODE_INFO);
EnvelopedEncodeInfo.hCryptProv = hCryptProv;
EnvelopedEncodeInfo.ContentEncryptionAlgorithm =
ContentEncryptAlgorithm;
EnvelopedEncodeInfo.pvEncryptionAuxInfo = NULL;
EnvelopedEncodeInfo.cRecipients = 1;
EnvelopedEncodeInfo.rgpRecipients = RecipCertArray;
//-------------------------------------------------------------------
// Get the size of the encoded message BLOB.
if(cbEncodedBlob = CryptMsgCalculateEncodedLength(
MY_ENCODING_TYPE, // message encoding type
0, // flags
CMSG_ENVELOPED, // message type
&EnvelopedEncodeInfo, // pointer to structure
szOID_RSA_signedData, // inner content OID
cbSignedBlob)) // size of content
{
printf("Length of the encoded BLOB will be %d.\n",cbEncodedBlob);
}
else
{
MyHandleError("Getting enveloped cbEncodedBlob length failed.");
}
//--------------------------------------------------------------------
// Allocate memory for the encoded BLOB.
if(pbEncodedBlob = (BYTE *) malloc(cbEncodedBlob))
{
printf("Memory has been allocated for the BLOB. \n");
}
else
{
MyHandleError("Enveloped malloc operation failed.");
}
//-------------------------------------------------------------------
// Open a message to encode.
if(hMsg = CryptMsgOpenToEncode(
MY_ENCODING_TYPE, // encoding type
0, // flags
CMSG_ENVELOPED, // message type
&EnvelopedEncodeInfo, // pointer to structure
szOID_RSA_signedData, // inner content OID
NULL)) // stream information (not used)
{
printf("The message to encode is open. \n");
}
else
{
MyHandleError("Enveloped OpenToEncode failed.");
}
//-------------------------------------------------------------------
// Update the message with the data.
if(CryptMsgUpdate(
hMsg, // handle to the message
pbSignedBlob, // pointer to the signed data BLOB
cbSignedBlob, // size of the data BLOB
TRUE)) // last call
{
printf("The signed BLOB has been added to the message. \n");
}
else
{
MyHandleError("Enveloped MsgUpdate failed.");
}
//-------------------------------------------------------------------
// Get the resulting message.
if(CryptMsgGetParam(
hMsg, // handle to the message
CMSG_CONTENT_PARAM, // parameter type
0, // index
pbEncodedBlob, // pointer to the enveloped,
// signed data BLOB
&cbEncodedBlob)) // size of the BLOB
{
printf("Enveloped message encoded successfully. \n");
}
else
{
MyHandleError("Enveloped MsgGetParam failed.");
}
//-------------------------------------------------------------------
// Clean up.
CertFreeCertificateContext(pRecipCert);
if(CertCloseStore(
hStoreHandle,
CERT_CLOSE_STORE_CHECK_FLAG))
{
printf("The certificate store closed without a certificate "
"left open. \n");
}
else
{
printf("The store closed but a certificate was still open. \n");
}
if(hMsg)
CryptMsgClose(hMsg);
if(hCryptProv)
CryptReleaseContext(hCryptProv,0);
} // end main
//-------------------------------------------------------------------
// This example uses the function MyHandleError, a simple error
// handling function to print an error message and exit
// the program.
// For most applications, replace this function with one
// that does more extensive error reporting.
void MyHandleError(char *s)
{
fprintf(stderr,"An error occurred in running the program. \n");
fprintf(stderr,"%s\n",s);
fprintf(stderr, "Error number %x.\n", GetLastError());
fprintf(stderr, "Program terminating. \n");
exit(1);
} // end MyHandleError